Alloy #11® A compensating alloymade of 99 percent copper and one percent nickel. It is used to makethe negative conductor that, inconjunction with pure copper, formsthermocouple extension wire for ASTM Type R and S thermocouples(platinum, platinum/rhodium). Alloy #11® is a registered trademark of Harrison Alloys. See “compensatingalloy.”

Alloy 188® A cobalt-based austeniticalloy that exhibits high strength andresistance to oxidation and corrosion.It is commonly used in the aerospace,nuclear, chemical and processindustries. Alloy 188® is a registeredtrademark of Haynes International.

Alloy 203/225 Alloys made up of 90 percent nickel and 10 percentchromium (203), and 98 percent nickeland two percent chromium (225). Theyform thermocouple extension wireconductors for Type D (W3Re/W25Re)thermocouples for applications under200°C (400°F). Type D is not an ASTMcalibration.

Alloy 214® A material that exhibitsexcellent resistance to oxidation,carburization and chlorine-bearingatmospheres. It is commonly used tomake sensor probe sheaths. Alloy 214® is a registered trademark of Haynes International.

Alloy 230® A material that exhibitsexcellent high temperature strength,oxidation resistance and long-termthermal stability. It works well innitriding environments, and iscommonly used to make sensor probesheaths. Alloy 230® is a registeredtrademark of Haynes International.

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GlossaryDefinitions ofCommonly UsedTerms Used inHeating, Sensing and ControllingIntroductionThe terms contained in this glossaryare defined according to their mostcommon use as they apply to heaters,temperature sensors, temperaturecontrollers and power controllers.Also included are terms used in thegeneral discussion of thermodynamictheory, thermal systems and heatenergy.

AA.G.A. See “American GasAssociation.”

abrasion resistance The ability of amaterial to resist mechanical wear.

absolute zero The temperature atwhich substances possess minimalenergy. Absolute zero is 0 Kelvin or 0° Rankine and is estimated to be -273.15°C (-459.67°F).

ac (Å) See alternating current.

ac line frequency The frequency ofthe alternating current power linemeasured in Hertz (Hz), usually 50 or60Hz.

ac/dc (ı) Both direct and alternatingcurrent.

accelerated aging A test thatsimulates the effects of long-termenvironmental and operatingconditions in a relatively short timeperiod.

accuracy Difference between thevalue indicated by a measuringinstrument and the corresponding truevalue. Sensor accuracy is based onUS NIST (NBS) standards.

action The response of an outputwhen the process variable is changed.See also “direct action,” and “reverseaction.”

active components An electronicdevice whose properties change witha change in the applied signal.Diodes, transistors and integratedcircuits are active components.

actual The present value of thecontrolled variable.

address An identification,represented by a name, label ornumber, of a register or location instorage, or any other data source ordestination, such as the location of astation in a communication network.

Advance® A thermocouple alloymade of 55 percent copper and 45percent nickel, used as the negativeconductor in ASTM Type E, J, and T thermocouples. Advance® is aregistered trademark of Harrison AlloysCompany.

alarm A signal that indicates that theprocess has exceeded or fallen belowthe set or limit point. For example, analarm may indicate that a process istoo hot or too cold.

alarm dead band An area of nocontrol or alarm change.

alarm delay The lag time before analarm is activated.

alarm hysteresis A change in the process variable required to re-energize the alarm output.

alarm module 1) A controllerhardware and software combinationconfigured to alert an operator orperform another function in responseto a problem in the thermal system. 2) A specific behavioral feature in theNAFEM (National Association of FoodEquipment Manufacturers) dataprotocol model that determines if analarm condition exists. It does this byproviding criteria to compare againstalarm object attributes.

alarm silence A feature that disablesthe alarm relay output.

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GlossaryAlloy 405/426 Alloys made of 94.5percent nickel, two percentmanganese, one percent silicon and1.5 percent aluminum (405), and 80percent nickel and 20 percent copper(426). They form thermocoupleextension wire conductors for use withType C (W5Re/W26Re) thermocouplesfor applications under 870°C (1600°F).Type C is not an ASTM calibration.

Alloy 556® A multipurpose alloy thatexhibits good resistance to sulfidizing,carburizing and chlorine-bearingenvironments. Alloy 556® is aregistered trademark of HaynesInternational.

Alloy HR160® A material that exhibitssuperior resistance to sulfides withgood resistance in some salt bathapplications. It is commonly used tomake sensor probe sheaths. AlloyHR160® is a registered trademark ofHaynes International.

alpha (A) The temperature coefficientof the change in electrical resistanceof a material measured inohms/ohm/°C. It indicates the basicchange in electrical resistance in amaterial for each °C in temperature.Alpha is a defining parameter forresistance temperature detectors(RTDs). For example, common alphasfor platinum RTDs are 0.00385 Ω/Ω/°C(DIN) or 0.003916 Ω/Ω/°C (JIS).

alternating current (ÅÅ) An electriccurrent that reverses at regularintervals, and alternates positive andnegative values.

Alumel® An alloy made of 95 percentnickel, two percent aluminum, twopercent manganese and one percentsilicon. It forms the negative conductorof ASTM Type K thermocouples.Alumel® is a registered trademark ofthe Hoskins Manufacturing Company.

ambient compensation See“compensation, ambient.”

ambient temperature See“temperature, ambient.”

American Gas Association (A.G.A.)Independent testing laboratory thattests gas-related appliances andaccessories to ANSI standards, or toA.G.A. standards in the absence of anationally-recognized standard.Watlow now uses nationallyrecognized testing laboratories toANSI standards for gas-relatedproducts, rather than A.G.A.

American Wire Gauge (AWG) A standard of the dimensionalcharacteristics of wire used to conductelectrical current or signals. AWG isidentical to the Brown and Sharpe (B & S) wire gauge.

ammeter An instrument that measuresthe magnitude of an electric current.

ampere (amp, A) A unit that definesthe rate of flow of electricity (current) ina circuit. Units are one coulomb (6.25x 1,018 electrons) per second.

analog A method of representing datausing the amplitude of a signal.

analog output A continuouslyvariable signal that is used torepresent a value, such as the processvalue or set point value. Typicalhardware configurations are 0 to 20mA, 4 to 20mA or 0 to 5VÎ(dc).

anneal To relieve stress in a solidmaterial by heating it to just below itsmelting point and then graduallycooling it to ambient temperature.Annealing usually lowers the tensilestrength while improving flexibility andflex life. Metals and glasses arecommonly annealed.

annunciator A visual display thatuses indicator lights to display theformer or existing condition of severalitems in a system.

ANSI American National StandardsInstitute. The United Statesgovernment agency that defines andmaintains technical standards.

anti-reset See “anti-reset windup.”

anti-reset windup The feature of aPID temperature controller thatprevents the integral (automatic reset)circuit from functioning when thetemperature is outside the proportionalband. This standard feature helpsstabilize a system. Also called “anti-reset.”

Application layer (OSI Layer 7) Thehighest layer of the seven-layer OSI(Open System Interconnection) modelwhere communication begins with aspecific application that comm-unicates with another device orsystem. All application-specificfunctions occur here, such as userauthentication and addressing. An e-mail application or web browser areexamples of the application layer forexchanging data over the Internet.The Application Layer resides abovethe Presentation Layer.

ARP (Address Resolution Protocol)The TCP/IP protocol that converts anIP address into a physical hardwareaddress, such as an address for anaddress for an Ethernet card.

ASME American Society ofMechanical Engineers.

ASTM American Society for Testingand Materials.

atmosphere The ambientenvironment.

atmosphere (atm) A standard unit ofpressure representing the pressureexerted by a 760 mm (29.92 in.)column of mercury at sea level at 45 degrees latitude and equal to 1,000g/cm2 (14.22 psi).

atmospheric pressure Pressure ingrams per square centimeter orpounds per square inch exerted by theearth’s atmosphere on bodies locatedwithin it.

block A set of things, such as words,characters or digits that are handledas a unit.

Block Check Character (BCC) Aserial communications error checkingmethod. An acceptable method formost applications, BCC is the defaultmethod. See “Cyclic RedundancyCheck (CRC).”

blocking voltage The maximumvoltage a surge protector can acceptwithout degrading its componentcurrent-protective devices.

boiling point The equilibriumtemperature between a liquid and agaseous state. For example, theboiling point of water is 100°C (212°F)at standard atmospheric pressure.

bonding The process of joining twosimilar or dissimilar materials. Intemperature sensors and lead wires,bonding usually establishes a sealagainst moisture. See “potting.”

braid A flexible covering formed fromplaited (served) textile or ceramicfibers or metallic filaments. Textile andceramic fibers are used to produceelectrical insulation around electricalconductors. Metallic filaments areused to add abrasion resistance orshielding from electrical noise.

bright annealing The description ofstainless steel or aluminum after finalsurface treatment, produced bypassing the metal between rollers witha moderately smooth surface. Thissurface treatment is used in theprocessing of aluminum sheets,stainless steel back plates, stainlesssteel cold rolled sheets and coldrolled strip steels.

browser A software application thatfinds and displays web pages. Alsocalled “web browser.”

BS British Standards. The UnitedKingdom agency that defines andmaintains technical standards.

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Glossaryatmospheric pressure, standardPressure exerted by the earth'satmosphere on bodies located withinit. Standard atmospheric pressure is14.7 psi (1.013 bar abs.) measured atsea level and 15°C (60°F).

automatic mode A feature that allowsthe controller to set PID control outputsin response to the process variable(PV) and the set point.

automatic power reset A feature inlatching limit controllers that does notrecognize power outage as a limitcondition. When power is restored, theoutput is re-energized automatically,as long as the temperature is withinlimits.

automatic prompts Data entry pointswhere a microprocessor-basedcontroller asks the operator to enter acontrol value.

automatic reset The integral functionof a PI or PID temperature controllerthat adjusts the process temperatureto the set point after the systemstabilizes. The inverse of integral.

auto-tune A feature that automaticallysets temperature control PID values tomatch a particular thermal system.

auxiliary output An output thatcontrols external activities that are notdirectly related to the primary controloutput. For example, door latches, gaspurges, lights and buzzers.

AWG See “American Wire Gauge.”

BB & S Gauge (Brown and SharpGauge) A standard of the dimensionalcharacteristics of wire used to conductelectrical current or signals. It isidentical to the American Wire Gauge.

B.T.E. thermocouple holes “Behind-the-element” ceramic tubes createelectrically isolated thermocoupleholes through Watlow ceramic fiberheaters. The holes are built into theheaters to very closely track elementtemperature for over-temperatureprotection and to improve heater life.

bandwidth A symmetrical regionabove and below the set point in whichproportional control occurs.

base metal thermocoupleThermocouples with conductors madeof base metallic element alloys (iron,copper, and nickel). Base metalthermocouples are ASTM Types E, J,K, N and T. They are usually used inlower temperature applications.

baud rate The rate of informationtransfer in serial communications,measured in bits per second.

BCC See “Block Check Character.”

bend radius (standard) The specifiedminimum radius to which a sensor (orwire) can be bent without stressing thestructure of the metal or damaging itselectrical transmitting characteristics.Standard bend radius is a function ofsensor (or wire) diameter.

beryllia/beryllium oxide (BeO) Awhite crystalline powder with a highmelting temperature (approximately2585°C or 4685°F, high thermalconductivity and high dielectricstrength. Used in high-temperatureceramic thermocouple insulation. Itsdust and particles are toxic. Specialprecautions are required whenhandling BeO.

blackbody An ideal surface thatabsorbs all incident radiation,regardless of wavelength, the directionof incidence and polarization. Itradiates the maximum energy possiblefor given spectral and temperatureconditions. A blackbody has anemissivity of 1.00. See “emissivity.”

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GlossaryBtu British Thermal Unit. A unit ofenergy defined as the amount of heatrequired to raise one pound of waterfrom 32°F to 33°F at standardatmospheric pressure. One Btu isequal to 0.293 watt-hours. Onekilowatt-hour is equal to 3,412 Btus.

bumpless transfer A smoothtransition from auto (closed loop) tomanual (open loop) operation. Thecontrol output(s) does (do) not changeduring the transfer.

burst fire A power control methodthat repeatedly turns on and off full accycles. Also called zero-cross fire, itswitches close to the zero-voltagepoint of the ac sine wave to minimizeradio frequency interference (RFI).Variable time-base burst fireselectively holds or transits ac cyclesto achieve the desired power level.

bushing The process of addingadditional sheath tubing to achieve alarger, non-standard diameter.

Ccabling Gathering insulated electricalconductors into a single cable.Methods include serving (braiding),extruding or wrapping.

Calendar van Dusen equation Aninterpolation equation that providesresistance values as a function oftemperature for RTDs.

calibration The comparison of ameasuring device (an unknown)against an equal or better standard.

calibration accuracy Differencebetween the value indicated by ameasuring instrument and a physicalconstant or known standard.

calibration offset An adjustment toeliminate the difference between theindicated value and the actual processvalue.

calorie A unit of energy defined as theamount of heat energy required toraise the temperature of one gram ofwater 1°C at 15°C.

carbon potential control The abilityto control the carbon content in steelinside heat treating furnaces.

cascade Control algorithm in whichthe output of one control loop providesthe set point for another loop. Thesecond loop, in turn, determines thecontrol action.

CAT.5 Category 5 wiring or cablemanufactured to the TIA/EIA 568-Astandard. The standard Ethernet wiringfor 10 Mbps or 100 Mbps networks infour twisted pairs; insulated,unshielded and jacketed cable.Terminated with RJ45 connectors inlengths of 100m or less.

CDA Confidential DisclosureAgreement. A legal document thatspells out the conditions andcircumstances by which confidentialinformation can be shared with anotherparty, and the remedies required forviolations. Companies typically useboth general CDAs and detailed CDAsthat cite specific intellectual propertyto protect. See “MCDA.”

CE A manufacturer’s mark thatdemonstrates compliance withEuropean Union (EU) laws governingproducts sold in Europe.

CE-compliant Compliant with theessential requirements of Europeandirectives pertaining to safety and/orelectromagnetic compatibility.

Celsius (C) Formerly known asCentigrade. A temperature scale inwhich water freezes at 0°C and boils at 100°C at standard atmosphericpressure. The formula for conversion to the Fahrenheit scale is: °F = (1.8 X °C) + 32.

central processing unit (CPU) Theunit of a computing system thatincludes the circuits controlling theinterpretation of instructions and theirexecution.

ceramic fiber An alumina-silica fiberthat is lightweight and low density. It isused as a refractory material.

ceramic insulation Materials made of metal oxides that are capable ofwithstanding high temperatures andproviding the desired dielectricstrength. They are used to insulateheater elements or thermocouplewires.

CFD Computational Fluid Dynamics.Numerical technique to solve andsimulate the behavior of the Navier-Stokes equation that describes fluidflow. Used by Watlow for thermalsystem simulation.

cfm Cubic feet per minute. Thevolumetric flow rate of a fluid. Whenused in gas flow, it is evaluated at agiven process temperature andpressure.

channel See “control channel.”

chatter The rapid on-off cycling of anelectromechanical relay or mercurydisplacement relay due to insufficientcontroller bandwidth. It is commonlycaused by excessive gain, littlehysteresis and short cycle time.

chemical resistance The ability of amaterial to resist permeation, erosionor corrosion caused by base, acid orsolvent chemicals.

Chromel® An alloy made ofapproximately 90 percent nickel and10 percent chromium that is used tomake the positive conductors of ASTMType E and K thermocouples.Chromel® is a registered trademark ofthe Hoskins Manufacturing Company.

circuit Any closed path for electricalcurrent. A configuration of electricallyor electromagnetically-connectedcomponents or devices.

client The client half of a client-serversystem where the client is typically anapplication (residing on a personalcomputer) that makes requests to aserver, computer with one or moreclients networked to it. E-mail is anexample of a client-server system.

conductivity Electrical conductivity isthe ability of a conductor to allow thepassage of electrons, measured in thecurrent per unit of voltage applied. It isthe reciprocal of resistivity. Thermalconductivity is the quantity of heatconducted through a body per unitarea, per unit time, per unit thicknessfor a temperature difference of 1 kelvin.

connection head A housing on asensor assembly. It provides a terminalblock for electrical connections, andallows the attachment of protectiontubes and cables or conduit hook-ups.

connectivity Computer jargon thatdescribes the readiness or capabilityof a device for communicating withother devices or systems.

Constantan A generic designation for a thermocouple alloy made of 55percent copper and 45 percent nickel that is used as the negativeconductor in ASTM Type E, J and Tthermocouples.

continuity check A test of finishedassemblies or wire that indicateswhether electric current flowscontinuously throughout the length ofthe material. It also shows a shortcircuit between conductors.

control accuracy The ability tomaintain a process at the desiredsetting. This is a function of the entiresystem, including sensors, controllers,heaters, loads and inefficiencies.

control action The response of thecontrol output relative to the differencebetween the process variable and theset point. For reverse action (usuallyheating), as the process decreasesbelow the set point, the outputincreases. For direct action (usuallycooling), as the process increasesabove the set point, the outputincreases.

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Glossaryclosed loop A control system thatuses a sensor to measure a processvariable and makes decisions basedon that input.

CMM 1) Cubic meters per minute, ameasure of airflow. 2) CoordinateMeasuring Machines, used fordimensional inspection inmanufacturing and qualityapplications. 3) Capability MaturityModel®, a registered trademarksoftware development managementmodel of the Software EngineeringInstitute (SEI), a research anddevelopment center sponsored by theU.S. Department of Defense andoperated by Carnegie MellonUniversity.

CNC Computerized NumericalControl. The programmed instructionsused by a class of cutting toolmachines (usually driven by designsoftware) for creating machined partsand molds.

coaxial cable A cylindricaltransmission cable made of aninsulated conductor or conductorscentered inside a metallic tube orshield, typically of braided wires. Itisolates the signal-carrying conductorfrom electrical interference or noise.

cold junction Connection pointbetween thermocouple metals and theelectronic instrument. See “referencejunction.”

cold junction compensationElectronic means to compensate forthe effective temperature at the coldjunction.

color code A system of standardcolors used to identify electricalconductors. For example, a color codeidentifies the thermocouple type inthermocouple circuits. Codes commonin the United States have ASTMdesignations. Color codes vary indifferent countries.

common-mode line filter A device tofilter noise signals on both power lineswith respect to ground.

common-mode rejection ratio Theability of an instrument to rejectelectrical noise, with relation to ground,from a common voltage. Usuallyexpressed in decibels (dB).

communications The use of digitalcomputer messages to linkcomponents. See “serialcommunications” and “baud rate.”

compensated connectors Athermocouple connector that useseither actual thermocouple alloycontacts or compensating alloycontacts. Maintaining metallic circuitproperties throughout the connectioncircuit reduces errors due tomismatched materials.

compensating alloy Any alloy thathas similar resistance to anotherthermocouple alloy. Compensatingalloys are usually low cost alternativesfor extension lead wire types. Forexample, Alloy #11 is a compensatinglead wire for platinum thermocouplesensors.

compensating loop An extra pair oflead wires that have the sameresistance as the actual lead wires, butare not connected to the RTD element.A compensating loop corrects leadwire resistance errors when measuringtemperature.

compensated, ambient The ability ofan instrument to adjust for changes inthe temperature of the environmentand correct the readings. Sensors aremost accurate when maintained at aconstant ambient temperature. Whentemperature changes, output drifts.

computer ground A line for theground connections to computers ormicroprocessor-based systems. It isisolated from the safety ground.

conduction The mode of heat transferwithin a body or between bodies incontact, caused by the junctionbetween adjacent molecules.

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Glossarycontrol channel Often synonymouswith “control loop.” In some markets,such as life sciences, its use mayindicate the presence of a datacommunications feature.

control loop A control system withfeedback (closed loop) from a singleload to the controller, or withoutfeedback (open loop) from the load to the controller.

control mode The type of action thata controller uses. For example, on-off,time proportioning, PID, automatic ormanual, and combinations of these.

controllability See “accuracy” and“control.”

convection A mode of heat transfer ina fluid (gas or liquid) in which heat istransferred through movement ofmasses of the fluid from a region ofhigher temperature to one of lowertemperature.

copper The positive conductor in anASTM Type T thermocouple. See“OFHC.”

cps Cycles per second. Frequency.Also referred to as Hertz.

CRC See “Cyclic RedundancyCheck.”

crosstalk Audio frequency signalinterference coupled from one signal-carrying conductor to an adjacentconductor.

cryogenic Related to lowtemperatures. Generally in the range of0° to -200°C (32° to -328°F).

CSA Canadian StandardsAssociation. An independent testinglaboratory that establishes commercialand industrial standards, tests andcertifies products.

C-UL® Canadian recognition ofUnderwriters Laboratories, Inc. (UL®)approval of a particular product class,such as UL® 508. In some instances,C-UL® approval may stand in lieu ofCanadian Standards Association(CSA) approval. All references to C-UL® stem from the original UL® fileonly, resident at the location of UL®

approval. See “CSA and “UL®”.

Cupron® A thermocouple alloy madeof 55 percent copper and 45 percentnickel. It is used in the negativeconductor of ASTM Type E, J and Tthermocouples. Cupron® is aregistered trademark of CarpenterTechnology.

current The rate of flow of electricity.The unit of measure is the ampere (A).1 ampere = 1 coulomb per second.

current transformer A transformerdesigned for measuring electricalcurrent.

cycle time The time required for acontroller to complete one on-off-oncycle. It is usually expressed inseconds.

Cyclic Redundancy Check (CRC) Anerror checking method incommunications. It provides a highlevel of data security, but is moredifficult to implement than Block CheckCharacter (BCC). See “Block CheckCharacter.”

DData Link Layer (OSI Layer 2) Thesecond layer of the seven-layer OSI(Open System Interconnection)protocol model that handles datapacket encoding and decoding to andfrom bits on a network. The Data LinkLayer has two sublayers, MediaAccess Control (MAC), and LogicalLink Control (LLC). The Data LinkLayer resides between the TransportLayer and the Physical Layer.

data logging A method of recording aprocess variable over a period of time.Used to review process performance.

dc (ÎÎ) Direct current. An electricalcurrent that flows in one direction.

dc resistance See “resistance.”

dead band The range through whicha variation of the input produces nonoticeable change in the output. In thedeadband, specific conditions can beplaced on control output actions.

decalibration An output shift in thethermocouple so that it no longerconforms to established standards.The shift is caused by the altering ofalloys in the thermocouple conductors.

default parameters The programmedvalues that are permanently stored inthe microprocessor software.

degree The increments in atemperature scale, or the incrementsof rotation of a dial. The location of areference point in electric or phase in acycle, in mechanical or electricalcyclic scales. One cycle is equal to360 degrees.

density Mass per unit volume of asubstance expressed in kilograms percubic meter of pounds per cubic foot

derivative The rate of change in aprocess variable. Also known as rate.See “PID.”

derivative control (D) The last term inthe PID control algorithm. Action thatanticipates the rate of change of theprocess variable and compensates tominimize overshoot and undershoot.Derivative control is an instantaneouschange of the control output in thesame direction as the proportionalerror. This is caused by a change inthe process variable (PV) thatdecreases over the time of thederivative (TD). The TD is in units ofseconds.

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GlossaryDeutsche Industrial Norm (DIN) Aset of technical, scientific anddimensional standards developed inGermany. Many DIN standards haveworldwide recognition.

deviation Any departure from adesired value or expected value orpattern. Sometimes referred to asdelta.

deviation alarm Warns when aprocess exceeds or falls below acertain range from the set point.Alarms can be referenced at a fixednumber of degrees, plus or minus, theset point.

DHCP Dynamic Host ConfigurationProtocol. A protocol that assigns anetwork device, a unique IP addresseach time it logs onto a network.

di/dt The time rate of change incurrent. Excessive di/dt can damage aphase-fired silicon controlled rectifier(SCR) power controller when it is usedfor large resistive loads. In this case,an inductor may be necessary toprotect the SCR.

dielectric An insulating material withvery low electrical conductivity.

dielectric breakdown The point atwhich a dielectric substance becomesconductive. Usually a catastrophicinsulation failure caused by excessivevoltage.

dielectric strength The potentialgradient at which electric failure orbreakdown occurs. Also known asbreakdown potential.

differential control A controlalgorithm where the set pointrepresents a desired differencebetween two processes. The controllerthen manipulates the second processto hold it at a set value relative to thefirst controller.

differential mode line filter A deviceto filter electrical noise between twopower lines.

diffusion A gradual mixing ofmolecules of two or more substancesthrough random thermal motion.

digital adaptive filter A filter thatrejects high frequency input signalnoise (noise spikes).

digital filter (DF) A filter that slows theresponse of a system when inputschange unrealistically or too fast.Equivalent to a standard resistor-capacitor (RC) filter.

DIN See “Deutsche Industrial Norm.”

direct action An output control actionin which an increase in the processvariable causes an increase in theoutput. Cooling applications usuallyuse direct action.

direct current (ÎÎ) An electric currentthat flows in one direction.

display capability In an instrumentwith digital display, the entire possiblespan of a particular parameter orvalue.

dissipation constant The ratio of thechange in internal power dissipation tothe resulting change in the bodytemperature of a thermistor.

distributed zero crossing (DZC) Aform of digital output control used byWatlow Anafaze in which the outputon-off state is calculated for everycycle of the ac line cycle. Power isswitched at the zero crossing point,reducing electrical noise. See “zero cross.”

distributed zero crossing (DZC) Aform of digital output control. Similar to burst fire.

DNS Domain Name Server. Acomputer that translates alphabeticinternet domain names into IP (Internetprotocol) addresses.

drain wire An uninsulated wire that isused as a ground conductor in wireand cable construction.

draw A manufacturing process actionthat pulls a material through a die tocompact the material.

drift A change in reading or value thatoccurs over long periods. Changes inambient temperature, componentaging, contamination, humidity andline voltage may contribute to drift.

droop In proportional controllers, thedifference between set point andactual value after the system stabilizes.The integral (reset) component of PIDcontrol corrects droop.

dual element sensor A sensor withtwo independent sensing elements.Usually used to measure temperaturegradients or provide redundancy in asingle point sensor assembly.

duplex control With enhancedsoftware, duplex control splits a singleprocess output into two individualoutputs. For example, a 4 to 20mAoutput is split into a 4 to12mA directaction (cooling) output and a 12 to20mA reverse action (heating) output,thus allowing one control output tofunction as two.

duplex wire A cable or wire with twoinsulated conductors that are parallelor twisted together. Duplexconstructions may also include adrain-wire conductor.

duty cycle The percentage of a cycletime in which the output is on.

dv/dt Time rate of change in voltage.Excess dv/dt can cause false turn onand destroy a silicon controlledrectifier (SCR) power controller. Loosewiring connections may arc andproduce this voltage change.

Eearth ground A metal rod, usuallycopper, that provides an electricalpath to the earth, to prevent or reducethe risk of electric shock.

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Glossaryefficiency The ratio of useful outputenergy (work) to input energy.

EIA See “Electronics Industries ofAmerica.”

EIA/TIA -232, -422, -423 and -485Data communications standards set bythe Electronic Industries of Americaand Telecommunications IndustryAssociation. Formerly referred to as RS(Recognized Standard).

EIA/TIA-232 (formerly RS-232) AnElectronics Industries of America(EIA)/Telecommunication IndustryAssociation (TIA) standard for interfacebetween data terminal equipment anddata communications equipment forserial binary data interchange. This isusually for communications over ashort distance (50 feet or less) and to asingle device.

EIA/TIA-485 (formerly RS-485) AnElectronics Industries of America(EIA)/Telecommunication IndustryAssociation (TIA) standard forelectrical characteristics of generatorsand receivers for use in balanceddigital multipoint systems. This isusually used to communicate withmultiple devices over a common cableor where distances over 50 feet arerequired.

elastomer Any material that returns toits original shape or dimensions afterbeing stretched or distorted.

electrical interference Electricalnoise that can obscure desiredinformation.

electrical noise See “noise.”

electrical-mechanical relay See“relay” and “electromechanical relay.”

electromagnetic compatibility (EMC)The ability of equipment or a system tofunction as designed in itselectromagnetic environment withoutintroducing intolerable electro-magnetic disturbances to thatenvironment, or being affected byelectromagnetic disturbances in it.

electromagnetic interference (EMI)Electrical and magnetic noise imposedon a system. There are many possiblecauses, such as switching ac poweron inside the sine wave. EMI caninterfere with the operation of controlsand other devices.

electromechanical relay A powerswitching device that completes orinterrupts a circuit by physicallyopening or closing electrical contacts.Not recommended for PID control.

electromotive force (EMF) Adifference in electrical potentialenergy, measured in volts.

Electronics Industries of America(EIA) An association in the US thatestablishes standards for electronicsand data communications.

electropolishing Creating a bright,smooth metal surface by depositing athin layer of another metal on it viaelectrolysis. Also, “electroplating.”

electrostatic discharge (ESD) Anelectrical discharge, usually of highvoltage and low current. For example,the shock that occurs when walkingacross a carpet.

EMC See “electromagneticcompatibility.”

EMF See “electromotive force.”

EMI See “electromagneticinterference.”

emissivity The ratio of radiationemitted from a surface compared toradiation emitted from a blackbody atthe same temperature.

endothermic A process that absorbsheat.

engineering units Selectable units ofmeasure, such as degrees Celsius andFahrenheit, pounds per square inch,newtons per meter, gallons per minute,liters per minute, cubic feet per minuteor cubic meters per minute.

enthalpy A property expressing therelative energy state of a gas or vaporat a given temperature, pressure andvolume. Expressed in units of Btu/lb orJoules/gram. It is used to evaluate theenergy change that occurs when avapor or gas is heated. Steam heatingproblems are readily solved using thisproperty.

EPROM Erasable, programmable,read-only memory inside the controller.

error The difference between thecorrect or desired value and the actualmeasured value.

ESD See “electrostatic discharge.”

e-Solutions A system that allowsWatlow's Authorized Distributors tocomplete business transactions withWatlow via the Internet. e-Solutionsallows Watlow's Distributors to orderproducts, to build products to meetspecifications, to check order statusand stock availability, and to access avariety of other features.

ETFE Ethylene tetrafluoroethylene, orTefzel®, the DuPont brand. See“Tefzel.”

Ethernet A local area network (LAN)protocol that supports a bus or star-configured network with speeds up to1,000 Mbps (megabits per second).

event An input or output signalrepresenting an on or off state. Eventscan control peripheral equipment orprocesses, or act as an input foranother control or control loop.

exothermic A process that releasesheat.

explosion-proof enclosure Anenclosure designed to withstand anexplosion of gases inside, to isolatesparks inside from explosive orflammable substance outside, and tomaintain an external temperature thatwill not ignite surrounding flammablegases or liquids.

FEP Fluorinated ethylene propylene.A fluorocarbon copolymer oftetrafluoroethylene andhexafluoropropulene. See “Teflon®.”

ferrule A tubular compressioncomponent used to mount atemperature sensing probe. It creates a gas-tight seal.

fiber, insulation Any nonmetallic,nonconductive textile that is used toinsulate conductors. Fibers may bebraided or wrapped.

field of view The target size ordistance necessary for an infraredsensor to receive 90 percent of thepower radiated by a surface.

FIREROD® A registered tradenamefor Watlow’s patented cartridge heater.

firmware A combination of softwareand hardware, where the software iswritten (embedded) into a ROM (readonly memory) chip, such as PROM(programmable read only memory) orEPROM (erasable programmable readonly memory).

fixed point A reproducibletemperature at the equilibrium pointbetween the phase changes in amaterial. For example, the triple pointof water at standard atmosphericpressure is 0.01°C (32.02°F).

flexibility The relative ease with whicha conductor can bend. See “bendradius.”

flow area The unobstructed area inthe cross section of a conduit that isavailable for fluid flow.

flow rate The actual volume of a fluidpassing through a section of a conduit.Flow rate may be measured in cubicfeet per minute, cubic meters persecond or other units.

FM See “Factory Mutual ResearchCorporation.”

FNPT informal; Female (internal)National Pipe Thread.

Form A — A single-pole, single-throwrelay that uses only the normally open(NO) and common contacts. Thesecontacts close when the relay coil isenergized. They open when power isremoved from the coil.

Form A or C — An electromechanicalrelay capable of Form A or Form Cfunction, selected with a jumper wire.

Form B — A single-pole, single-throwrelay that uses only the normallyclosed (NC) and common contacts.These contacts open when the relaycoil is energized. They close whenpower is removed from the coil.

Form C — A single-pole, double-throwrelay that uses the normally open (NO),normally closed (NC) and commoncontacts. The operator can choose towire for a Form A or Form B contact.

fpm Feet per minute. A measure offlow velocity. When used in gas flow, itis evaluated at a specific processtemperature and pressure.

fps Feet per second. A measure offlow velocity. When used in gas flow, itis evaluated at a specific processtemperature and pressure.

freezing point The fixed temperaturepoint at which a material changes froma liquid to a solid state. This is thesame as the melting point for purematerials. For example, the freezingpoint of water is 0°C or 32°F.

frequency The number of cycles overa specified period of time, usuallymeasured in cycles per second. Alsoreferred to as Hertz (Hz). Thereciprocal is called the period.

fuse A device that protects electriccircuits by interrupting power in acircuit when an overload occurs.Silicon controlled rectifiers (SCRs)require special, fast acting fuses,sometimes referred to as I2t (amps2-seconds) fuses.

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Glossaryexposed junction A type ofthermocouple probe in which the hot,or measuring, junction protrudesbeyond the sheath material and is fullyexposed to the substance beingmeasured. It usually gives the fastestresponse time. No electrical isolation isprovided.

extension wire See “thermocoupleextension wire.”

external transmitter power supply Adc voltage source that powers externaldevices.

extrusion A process by which amaterial is melted and pushed orpulled through a die to create adesired shape.

FFahrenheit The temperature scalethat sets the freezing point of water at32°F and its boiling point at 212°F atstandard atmospheric pressure. Theformula for conversion to Celsius is: °C = 5⁄9 (°F - 32°F).

failed sensor alarm Warns that aninput sensor no longer produces avalid signal. For example, when thereare thermocouple breaks, infraredproblems, or resistance temperaturedetector (RTD) open or short failures.

FEA Finite Element Analysis. AWatlow Research and Developmentmethod of using a computer simulationto create a thermal model of a heateror heated part, saving the time andexpense of multiple prototype builds.FEA optimizes the heater design withan accurate prediction of the expectedtemperature uniformity.

FEM Finite Element Method. Anumerical technique to solve andsimulate the behavior of differentialequations, used for thermal systemsimulation.

Teflon® is a registered trademark of E.I. duPontde Nemours & Company.

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Glossaryfuzzy logic A type of artificialintelligence logic that uses apercentage match to representvariable or inexact data, rather thanthe exactly true (1) or false (0) ofbinary logic.

Ggain The amount of amplification usedin an electrical circuit. Gain can alsorefer to the proportional (P) mode ofPID.

GGS Glass Glass Silicone. Anoptional heater lead wire covering, forWatlow cartridge or multicoil tubularheaters, made with two layers offiberglass and a silicone binder.

giga (G) A prefix that means 109 (onebillion in the US). Note: The wordbillion refers to different numbers inEurope and the US. In the US a billion is one thousand million(1,000,000,000). In Germany, England,France and other countries, a billion isone million million (100,000,000,000).That is a trillion in the US.

global alarm Alarm associated with a global digital output that is cleareddirectly from a controller or through auser interface.

gph Gallons per hour. A measure ofthe volumetric flow rate of a fluid.

gpm Gallons per minute. A measureof the volumetric flow rate of a fluid.

green rot See “preferentialoxidation.”

ground An electrical line with thesame electrical potential as thesurrounding earth. Electrical systemsare usually grounded to protect peopleand equipment from shocks due tomalfunctions. Also called “safetyground.”

ground loop A condition createdwhen two or more paths for electricityare created in a ground line, or whenone or more paths are created in ashield. Ground loops can createundesirable noise.

grounded potential The electricalpotential of the earth. A circuit, terminalor chassis is said to be at groundpotential when it is used as a referencepoint for other potentials in the system.

grounded junction Type ofthermocouple probe in which the hot,or measuring junction, is an integralpart of the sheath material. Noelectrical isolation is provided.

GUI Graphic User Interface. Arepresentation, on a computer screen,of a system or process that allows thecomputer user to interact with thesystem or process.

HHAI-KN® A thermocouple alloy madeof 95 percent nickel, two percentaluminum, two percent manganeseand one percent silicon that is used asthe negative conductor of ASTM Type K thermocouples. HAI-KN® is aregistered trademark of the HarrisonAlloys Company.

HAI-KP® A thermocouple alloy madeof 90 percent nickel and 10 percentchromium used in the positiveconductor of ASTM Type K and Ethermocouples. HAI-KP® is aregistered trademark of the HarrisonAlloys Company.

Hastelloy® A family of related alloys(X, Alloy B2 and C276). Hastelloy® is a registered trademark of HaynesInternational.

HDPE Chemical abbreviationrepresenting high-density polyethyleneplastics.

heat Energy transferred betweenmaterial bodies as a result of atemperature difference between them.See “Btu,” “calorie” and “Joule.”

heat transfer The flow of heat energyfrom one body of higher temperatureto one of lower temperature.

heat treating thermocouple See“thermocouple” and “heat treating.”

heat/cool output filter A filter thatslows the change in the response ofthe heat or cool output. The outputresponds to a step change by going toapproximately 2⁄3 its final value withinthe number of scans that are set.

heated insulation concept Adescription of one of the major featuresof the ceramic fiber heater product linefrom Watlow Columbia, that theinsulation and heater element exist inone package.

heat sink Any object that conductsand dissipates heat away from anobject in contact with it. Also a finnedpiece of metal, usually aluminum, thatis used to dissipate heat generated byelectrical and electronic devices.

Hertz (Hz) Frequency, measured incycles per second.

high deviation alarm Warns that theprocess exceeds the set point by thehigh deviation value or more. It can beused as either an alarm or controlfunction.

high process alarm Warns that theprocess exceeds a set value. It can beused as either an alarm or controlfunction.

high process variable See “processvariable.”

high reading An input level thatcorresponds to the high process value.For linear inputs, the high reading is apercentage of the full scale inputrange. For pulse inputs, the highreading is expressed in cycles persecond (Hertz, Hz).

hi-pot test A test that applies a highvoltage to a conductor to assure theintegrity of the surrounding insulation.See “dielectric breakdown.”

hole fit The gap between thecartridge heater sheath and the part itfits into. The smaller this gap, thebetter the heater transfer to the part.

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Glossaryhot change A feature of ceramic fiberand band heaters that allows individualheater replacement without totalsystem shutdown or disassembly.

HTML Hypertext Markup Language.HTML uses tags and attributes toformat documents displayed on a webbrowser.

HTTP Hypertext Transfer Protocol.The protocol used by the worldwideweb that defines messages andtransmissions between servers andclients.

hub connecting point in a star-configured LAN (local area network). Ahub gathers individual network nodestogether.

hunting Oscillation of a process valuenear the set point.

Hypalon® A synthetic rubber,chlorosulfonated polyethylene.Hypalon® is a registered trademark ofthe E.I. duPont de Nemours &Company.

hysteresis A change in the processvariable required to re-energize thecontrol or alarm output. Sometimescalled switching differential.

II.D. Inside diameter.

ice point The temperature at whichpure water changes from a liquid to asolid (freezes). 0°C (32°F).

idle set point Desired control valueafter a timing period.

IETF Internet Engineering Task ForceA collection of expert volunteers whoby consensus set the engineeringstandards for Internet technology. TheIETF is overseen by the InternetSociety, an international, non-profit,membership organization focused onthe expansion of the Internet.

IFC heated part Interference FitConstruction. A manufactured part witha specially designed groove milled intoit with an IFC heater elementpermanently formed into the groove,creating intimate contact between theelement and the part. IFC heated partsoffer an alternative to milled grooveheaters and brazed heater assembliesfor application with temperatures toohigh for aluminum “cast-in” heatedparts, or for environments where castaluminum cannot be used.

i-key A toggle-action information keyon controllers that provides contextsensitive help in a display. Typicallycolored as “highway information signblue,” i.e., Pantone 293C or equivalent.

impedance (Z) The total opposition ofa circuit to the flow of alternatingcurrent. It includes resistance andreactance, and is measured in ohms.

Incoloy® A family of related alloys(800, 800X and 825). A registeredtrademark of the Special MetalsCorporation (formally Inco).

Incoloy® 800 The standard heaterprotective sheath material, a nickel-iron-chromium alloy, and registeredtradename of Special MetalsCorporation, used for the WatlowFIREROD® heater. Incoloy® 800 isvery corrosion- and temperature-resistant, and a key to the long-livedFIREROD® in high-temperatureapplications.

Inconel® A family of related alloys(600, 601, 625, X750). A registeredtrademark of the Special MetalsCorporation (formerly Inco).

indication accuracy Closenessbetween the displayed value and ameasured value. Usually expressed asa + or -, a percent of span or numberof digits.

infrared A region of theelectromagnetic spectrum withwavelengths ranging from one to 1,000microns. These wavelengths are mostsuited for radiant heating and infrared(non-contact) temperature sensing.

initial calibration tolerance Theallowable deviation from the theoreticalEMF value generated by any particularthermocouple type at a giventemperature. See “limit of error.”

input Process variable informationthat is supplied to the instrument.

input scaling The ability to scaleinput readings (readings in percent offull scale) to the engineering units ofthe process variable.

input type The signal type that isconnected to an input, such asthermocouple, RTD, linear or process.

installed power Amount of powerused for an application or process. It isthe same as the kilowatt (kW) rating ofinstalled heaters.

Instrument Society of America (ISA)An engineering society that definesand maintains standards for scientificand technical measuring devices.

insulation A material that electricallyisolates a conductor from itssurroundings, or thermally isolates anobject from its surroundings.

insulation resistance The capacity ofan insulation material to resist the flowof electricity. Expressed in ohms. See“dielectric strength.”

integral Control action thatautomatically eliminates offset, ordroop, between set point and actualprocess temperature. See “reset” and“automatic reset.”

integral control (I) A form oftemperature control. The I of PID. See “integral.”

interchangeability The ability tointerchange system components withminimum effect on system accuracy.

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GlossaryIP One of two primary protocols thatinternet hosts use. IP describes themessage packet (datagrams orsegment of messages) format. IP isnetwork layer protocol defined by theIETF. See “TCP” and “TCP/IP.”

IPTS48, 68 International PracticalTemperature Scales of 1948 and 1968.These have been superseded byITS90. See “ITS90.”

iron The positive conductor in ASTMType J thermocouples.

ISA See “Instrument Society ofAmerica.”

isolation junction A form ofthermocouple probe construction inwhich the measuring junction is fullyenclosed in a protective sheath andelectrically isolated from it. Commonlycalled an ungrounded junction.

isolation Electrical separation ofsensor from high-voltage circuitry.Allows use of grounded or ungroundedsensing element.

isothermal A process, volume or areathat maintains a constant temperature.

ITS90 International Temperature Scaleof 1990. The standard scale made offixed points that closely approximatethermodynamic temperatures. Alltemperatures between the fixed pointsare derived by interpolation using theassigned interpolation instrument.Adopted in late 1993, this scalereplaces both IPTS48 and 68.

Jjacket The outer covering on a wire orcable. It may provide electricalinsulation and/or resistance tochemicals, abrasion and moisture.

JDA Joint Development Agreement.Specifies what role each party agreesto when developing a new product.

JIS See “Joint Industrial Standards.”

job A set of operating conditions for aprocess that can be stored andrecalled in a controller’s memory. Also called a recipe.

Joint Industrial Standards (JIS) AJapanese agency that establishes andmaintains standards for equipmentand components. Also known as JISC(Japanese Industrial StandardsCommittee), its function is similar toGermany’s Deutsche Industrial Norm(DIN).

Joule A basic unit of heat energy,equal to the work done when a currentof one ampere is passed through aresistance of one ohm for one second.

junction The point where twodissimilar metal conductors join to forma thermocouple.

KKapton® A lightweight organicpolymer film that is a versatiledielectric material because of itstensile strength, dimensional stabilityand low emission of gas in vacuums. Aregistered trademark of the E.I. duPontde Nemours & Company.

Kelvin (k) An absolute temperaturescale. Zero Kelvin is absolute zero. No degree symbol (°) is used with theKelvin scale. (0°C = 273.15K, 100°C = 373.15K).

kilo (k) A prefix meaning thousand.

kilowatt (kW) Unit of electrical powerequal to 1,000 watts or 3,412 Btus perhour when the power factor equals 1.0.

kilowatt hour (kWh) Unit of electricalenergy, or work, expended by onekilowatt in one hour. Also expressed as1,000 watt hours.

KN A thermocouple alloy made of 95 percent nickel, two percentaluminum, two percent manganeseand one percent silicon that is used inthe negative conductor of ASTM TypeK thermocouples. Manufacturertrademarks for KN include Alumel®,Nial® and HAI-KN®.

KP A thermocouple alloy made of 90percent nickel and 10 percentchromium that is used in the positiveconductors of ASTM Type E and Kthermocouples. Manufacturertrademarks for KP include Chromel®,Tophel® and HAI-KP®.

kVA Kilovoltampere or 1,000voltamperes (VA). One unit of apparentpower equals 1VA.

k-value The measure of a material'sthermal conductivity coefficient or itsability to conduct heat. Copperconducts better than plastic; copperhas a higher k value. The k-value isexpressed in W/cmK (watt percentimeter Kelvin) or in Btu/hft.F (Btuper hour per ft. degree Fahrenheit).The k-value is the reciprocal of the R-value, thermal resistance.

LLA Lead Adaptor. Watlow's patentedmethod for adding a variety of optionsfor leads and lead protection to stockheaters.

ladder logic An electrical circuitdiagram schematic style that arrangesthe positive and negative sides of thepower input as the two main beams ofa vertical ladder, and arranges theconnections between them as therungs of the ladder.

lag The amount of time delay betweentwo related parts of a process orsystem.

Nial® and Tophel® are registered trademarks ofCarpenter Technology (Car Tech).Chromel® and Alumel® are registeredtrademarks of Hoskins ManufacturingCompany.

HAI-KN® and HAI-KP® are registeredtrademarks of Harrison Alloys Company.

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GlossaryLAN Local Area Network. A computernetwork in a single physical location.LANs can be connected together in aWide Area Network (WAN).

latent heat of fusion (HF) The amountof heat energy, expressed in Btu/lb orJoule/gram, required to change a solidto a liquid without an increase intemperature.

latent heat of vaporization (HV) Theamount of heat energy, expressed inBtu/lb or Joule/gram, required tochange a liquid to a vapor without anincrease in temperature.

lava cone Low temperature silicate-based insulator used betweenelectrically conductive and non-conductive casings or tubes.

LCP Liquid Crystal Polymer. A high-temperature thermoplastic withgood impact strength.

LED See “light emitting diode.”

leg One connection in an electriccircuit.

light emitting diode (LED) A solid-state electronic device thatglows when electric current passesthrough it.

limit of error A tolerance band of thethermal electric response ofthermocouple wire, expressed as apercentage or a specific degree valuein defined temperature ranges, definedby the ASTM specification MC96.1(1982).

limit or limit controller A highlyreliable, discrete safety device(redundant to the primary controller)that monitors and limits thetemperature of the process, or a pointin the process. When temperatureexceeds or falls below the limit setpoint, the limit controller interruptspower through the load circuit. A limitcontroller can protect equipment andpeople when it is correctly installedwith its own power supply, power lines,switch and sensor.

linear input A process input thatrepresents a straight line function.

linearity The deviation in responsefrom an expected or theoreticalstraight line value for instruments andtransducers. Also called linearity error.

linearization, input See“linearization” and “square root.”

linearization, square root Theextraction of a linear signal from anonlinear signal corresponding to themeasured flow from a flow transmitter.Also called square root extraction.

liquid crystal display (LCD) A type ofdigital display made of a material thatchanges reflectance or transmittancewhen an electrical field is applied to it.

load The electrical demand of aprocess, expressed in power (watts),current (amps) or resistance (ohms).The item or substance that is to beheated or cooled.

local set point The primary set point.

loop See “control loop.”

loop alarm Any alarm system thatincludes high and low process,deviation band, dead band, digitaloutputs, and auxiliary control outputs.

loop resistance The total resistanceof the conducting materials in athermocouple circuit.

low deviation alarm Warns that theprocess is below the set point by thelow deviation value or move processvariable. It can be used as either analarm or control function.

low process alarm Warns that theprocess is below a set value. It can beused as either an alarm or controlfunction.

low process variable See “processvariable.”

low reading An input levelcorresponding to the low processvalue. For linear inputs, the lowreading is a percentage of the fullscale input range. For pulse inputs, thelow reading is expressed in cycles persecond, Hertz (Hz).

Mmanual mode A selectable modewithout automatic control. The operatorsets output levels. Same as open loopcontrol.

manual reset 1) A feature on a limitcontrol that requires humanintervention to return the limit to normal operation after a limit conditionhas occurred. 2) The adjustment of a proportional control to raise theproportional band to compensate for droop.

mass flow rate The amount of asubstance that flows past a givencross-section area of a conduit in agiven unit of time.

master A device that transmits a setpoint signal to other controllingdevices, called remotes.

maximum load impedance Thelargest load that the output device canoperate. Usually specified in ohms.

maximum operating temperatureThe highest temperature at which adevice can operate safely, or withexpected normal service life.

maximum power rating Themaximum operating power at which adevice can operate safely or withexpected normal operating life.

MCDA Mutual Confidential DisclosureAgreement. A legal document thatspells out mutual provisions for bothparties, and the conditions andcircumstances in which confidentialinformation can be shared by bothparties, and the remedies required forviolations.

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GlossaryMDR See “relay, mercurydisplacement.”

measuring junction See “junction.”

measuring junction Thethermocouple junction that is affixed toor inserted into the material beingmeasured. Also called hot junction.

mega (M) A prefix that means one 106

(one million in the US).

megawatt (MW) 1x106 watts or1,000,000 (one million) watts.

melting point The temperature atwhich a substance changes from asolid to liquid state. This is the same asthe freezing point of pure materials.

menu A list of options from which theoperator can select the tasks to bedone.

mercury displacement relay (MDR)A power switching device in whichmercury, displaced by a plunger,completes the electric circuit acrosscontacts.

metal fatigue A breakdown in metalstrength caused by mechanical action.For example, when sheath andconductor materials have differentlinear expansion coefficients, heatingand cooling cause mechanicalmovement that induces strain. Metalfatigue shortens the life of the heaterand the thermocouple.

MGT Mica Glass Teflon®. An optionalheater lead wire covering, used withseveral Watlow heater lines, made withmica, fiberglass and a Teflon® binder.

MI leads Mineral Insulated leads. AWatlow LA (Lead Adaptor) terminationoption for cartridge heaters thathandles both high temperatures up to815°C (1,500°F) and contamination,such as moisture, gases, oils, plasticdrool, solvents and water.

MIB Management Information Base Adatabase of defined properties ofobjects that can be monitored ormanipulated by a networkadministrator via an SNMP agent.

mica A silicate material used primarilyas an electrical and heat insulator.

micron A unit of length. One micron isequivalent to 10-6 meters.

microvolt (µV) One 10-6 of a volt (one millionth in the US).

mil One thousandth of an inch, or0.001 inches in decimal form.

milled groove A machined groovemilled into a part to accept a heatershaped to fit the groove.

milliampere (mA) One 10-3

(thousandth) of an ampere.

millivolt (mV) One 10-3 (thousandth)of a volt.

mineral insulated thermocouple Athermocouple probe constructed byloading a metal sheath withthermocouple conductors and amineral-based dielectric material, thencompacting the entire assembly.

minimum load current The smallestload current required to ensure properoperation of an output switchingdevice.

minimum output impedance See“offstate impedance.”

MNPT informal; Male (external)National Pipe Thread.

MO Magnesium Oxide. Thepowdered chemical compound usedin heater manufacturing to insulate theresistance wire from the metal sheath.This high grade material alsocontributes to the long life of Watlowheaters.

MODBUS™ protocol driver Asoftware program subroutine thatconverts programming language- oroperating system-specific instructionsto the MODBUS™ protocol for aMODBUS™ device.

moisture resistance The relativeability to resist permeation by water.

Monel® An alloy made of nickel andcopper sensor sheath that is used tomake sensor sheaths. It exhibitsexcellent resistance to sea water; tohydrofluoric, sulfuric and hydrochloricacids; and to most alkalis. Monel® is aregistered trademark of the SpecialMetals Corporation (formally Inco).

multilayer hybrid A hybrid circuitconstructed of alternating conductiveand insulating layers. The multilayerstructure combines very densepackaging of electronics with goodability to remove generated heat.Multilayers are typically built throughrepeated firings as layers are addedand are typically constructed withgold, silver-palladium or copperconductors.

Mylar® Terephtalate (polyester) film. Aregistered trademark of the E.I. duPontde Nemours & Company.

NNational Bureau of Standards (NBS)Now called the National Institute ofStandards Technology (NIST).

National Electrical Code (NEC) A setof specifications devised for the safeapplication and use of electric powerand devices in the United States.

National Electrical ManufacturersAssociation (NEMA) A United Statesassociation that establishesspecifications and ratings for electricalcomponents and apparatuses.Conformance by manufacturers isvoluntary.

National Institute of Standards andTechnology (NIST) A United Statesgovernment agency responsible forestablishing scientific and technicalstandards. Formerly the NationalBureau of Standards.

National Pipe Thread (NPT) Thetaper pipe thread standard used inNorth America.

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GlossaryNBS See “National Bureau ofStandards.”

NEC See “National Electrical Code.”

negative temperature coefficient Adecrease in electrical resistance thatoccurs with a temperature increase.See “thermistor.”

NEMA See “National ElectricalManufacturers Association.”

NEMA 4X A NEMA specification fordetermining resistance to moistureinfiltration and corrosion resistance.This rating certifies the controller aswashable and corrosion resistant.

neoprene A synthetic rubber, alsoreferred to as polychloroprene, thatexhibits good resistance to oil,chemicals and flame.

NetBios Network Basic Input OutputSystem. An application programminginterface (API) that adds specialnetwork functions to a computer’sbasic operating system.

Network Layer (OSI Layer 3) Thethird layer of the seven-layer OSI(Open System Interconnection)protocol model that handles switching,routing, and packet sequencingbetween nodes on a network. TheNetwork Layer resides between theTransport Layer and the Data LinkLayer.

Nial® A thermocouple alloy made of95 percent nickel, two percentaluminum, two percent manganeseand one percent silicon that is used inthe negative conductor of ASTM Type K thermocouples. Nial® is aregistered trademark of CarpenterTechnology.

nicrosil A thermocouple alloy that ismade of 84.6 percent nickel, 14.0percent chromium and 1.4 percentsilicon. It is used in the positiveconductor of an ASTM Type Nthermocouple.

nisil A thermocouple alloy that ismade of 95.6 percent nickel and 4.4 percent silicon. It is used in thenegative conductor of an ASTM Type N thermocouple.

NIST See “National Institute ofStandards and Technology.”

no key reset A method for resettingthe controller's memory (for instance,after an EPROM change).

noble metal thermocouple Thegeneral designation for thermocoupleswith conductors made of platinumand/or platinum alloys (ASTM Types B,R and S). They are used in high-temperature or corrosive applications.

node A connection point on acomputer network for one computer orother addressable device, such as aprinter.

no-heat The part of a Watlow heaterintentionally designed as unheated, oras an unheated extension, outside theresistance wire (heater coil) area. Theno-heat area has a lower temperaturedue to heat losses of various types:radiation; conduction; or convection.

noise Unwanted electrical signals thatusually produce signal interference insensors and sensor circuits. See“electromagnetic interference (EMI).”

noise suppression The use ofcomponents to reduce electricalinterference that is caused by makingor breaking electrical contact, or byinductors.

Nomex® A temperature-resistant,flame retardant nylon compound that isused as a wire insulation. A registeredtrademark of E.I. duPont de Nemours& Company.

NPT See “National Pipe Thread.”

NPT American National StandardTaper Pipe Thread as defined by ANSIB1.20.1.

NSF 1) National SanitationFoundation; 2) National ScienceFoundation.

NUWARMTH® A Watlow wholly-owned subsidiary that produces andmarkets consumer-focusedthermopolymer products primarily forthe home and automotive industries.

nylon A thermoplastic that iscommonly used as an insulationbecause it exhibits excellent abrasionand good chemical resistance.

OO.D. Outside diameter.

offset Synonym for “droop.” In astable thermal system, the differencebetween the process set point and theprocess actual temperature. An offsetvariable can be introducedintentionally into the system by somecontrollers to compensate for sensorplacement. In PID control, integral(reset) will eliminate droop.

offstate impedance The minimumelectrical resistance of the outputdevice in the off, or de-energized,state. It is based on the frequency ofthe load supply current plus internaland/or external noise suppressiondevices.

OFHC Oxygen-free, high conductivitycopper. The pure copper used in thepositive conductor of a an ASTM Type T thermocouple.

ohm (Ω) The unit of electricresistance. The resistance valuethrough which one volt will maintain a current of one ampere. See “Ohm’sLaw.”

Ohm’s Law Current in a circuit isdirectly proportional to the voltage,and inversely proportional toresistance; stated as: E = IR, I = E/R,R = E/I, P = EI where 1 = current inamperes, E = EMF in volts, R = resistance in ohlms and P = power in watts.

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GlossaryOID ("oh-eye-dee") Object IDentifier.In the NAFEM (National Association ofFood Equipment Manufacturers)context, Object Identifiers form anindex of attributes of a supplier'sprogrammable objects in a dataprotocol model. Object identifiersderive from the SNMP standard.

on-off A method of control that turnsthe output full on until set point isreached, and then off until the processerror exceeds the hysteresis.

on-off controller A temperaturecontroller that operates in either full-onor full-off state.

open loop A control system with nosensory feedback. See “manualmode.”

operator menus The menusaccessible from the front panel of acontroller. These menus allowoperators to set or change variouscontrol actions or features.

optical isolation Two electronicnetworks that are connected throughan LED (light emitting diode) and aphotoelectric receiver. There is noelectrical continuity between the twonetworks.

OSHA Occupational Safety andHealth Act. Also the OccupationalSafety and Health Agency, the UnitedStates governmental agency thatestablishes and enforces safetystandards in the workplace.

OSI Reference Model (Open SystemInterconnection, ISO/IEC 7498-1) Aseven-layered model for developingand implementing communicationamong systems. Control passes fromone layer to the next and back again,beginning at the application layer inthe system that initiates thecommunication. The reference modelprovides a common basis for thecoordination of standardsdevelopment for the purpose ofsystems interconnection from ISO/IEC 7498-1.

output The control signal that affectsthe and process value.

output type The form of PID controloutput, such as time proportioning,distributed zero crossing, serial digital-to-analog converter or analog. Also thedescription of the electrical hardwarethat makes up the output.

overshoot The amount by which aprocess variable exceeds the set pointbefore it stabilizes.

PP control Proportioning control.

panel lock A feature that preventsoperation of the front panel.

parallel circuit A circuit configurationin which the same voltage is applied toall components, with current dividedamong the components according totheir respective resistances orimpedances.

parameter 1. A variable that is given aconstant value for a specificapplication or process. 2. A value thatdetermines the response of anelectronic controller to given inputs.

passivation A process for treatingstainless steel surfaces, usually withdilute nitric acid to removecontaminants, and to apply a passivefilm protecting the fresh metal surface.

passive component A componentwhose properties do not change withchanges in the applied signal.Resistors, capacitors and inductorsare passive components.

PC See “polycarbonate.”

PD control Proportioning control withderivative (rate) action.

PDR control Proportional derivativecontrol with manual reset, used in fastresponding systems where the resetcauses instabilities. With PDR control,an operator can enter a manual resetvalue that eliminates droop in thesystem.

PEI See “polyetherimide.”

Peltier Effect Inverse of Seebeckeffect, used in thermoelectricapplications. See “Seebeck” effect.

percent power control Open-loopcontrol with output power set at aparticular level.

percent power limit Restriction ofoutput power to a predetermined level.

PET Chemical abbreviation forpolyethylene terephthalate.

PFA Chemical abbreviationrepresenting a perfluoroalkyl group.See “Teflon®.”

phase The time-based relationshipbetween alternating current cycles anda fixed reference point. In electricity, itis usually expressed in angulardegrees, with a complete cycle equalto 360˚. It describes the relationshipsof voltage and current of two or morealternating waveforms.

phase-angle firing A mode of powercontrol in silicon controlled rectifiers(SCRs). Phase-angle firing varies thepoint at which the SCR switchesvoltage inside the AC sine wave.

Physical Layer (OSI Layer 1) Thefirst and lowest layer of the seven-layerOSI (Open System Interconnection)protocol model where bits ofinformation move through the physicalmedium or space. The Physical Layerincludes the hardware means ofmoving the information. The PhysicalLayer resides below the Data LinkLayer.

PI control Proportioning control withintegral (automatic reset) action.

PID Proportional, Integral, Derivative.A control mode with three functions:proportional action dampens thesystem response, integral corrects fordroop, and derivative preventsovershoot and undershoot.

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Glossaryping Packet Internet groper. Acomputer utility used to troubleshootInternet connections. Ping verifies thata specific IP address is available.

plastic Natural and syntheticpolymeric substances, excludingrubbers, that flow under heat and/orpressure. See http://www.plasticstechnology.com/materials/index.html for an extensive materialsdatabase, including abbreviations,properties, features, etc.

Platinel® A nonstandard platinumalloy with thermoelectriccharacteristics that closely matchASTM Type K thermocouples attemperatures above 800°C (1440°F).Platinel® is a registered trademark ofEnglehard Industries.

platinum (Pt 2) A noble metal that ismore ductile than silver, gold orcopper, and has excellent chemicaland heat resistant characteristics. It isused in the negative conductor inASTM Types R and S thermocouples. platinum 10 percent rhodium Theplatinum-rhodium thermocouple alloythat forms the positive conductor onASTM Type S thermocouples. platinum 13 percent rhodium Theplatinum-rhodium thermocouple alloythat forms the positive conductor onASTM Type R thermocouples.

platinum 30 percent rhodium Theplatinum-rhodium thermocouple alloythat forms the positive conductor onASTM Type B thermocouples.

platinum 6 percent rhodium Theplatinum-rhodium thermocouple alloythat forms the negative conductor onASTM Type B thermocouples.

platinum 67 An NIST platinumstandard. Platinum 67 is used tointerpolate the temperature scalebetween 630.74 and 1064.43°C(1167.33 and 1947.97°F). Replacingplatinum 27, platinum 67 (IPTS68) isnine microvolts negative to platinum 27.

polarity The electrical quality ofhaving two opposite poles, onepositive and one negative. Polaritydetermines the direction in which acurrent tends to flow.

poll engine A software applicationdedicated to continuously requestingdata from connected devices on anetwork.

polycarbonate (PC) A thermoplasticthat offers high strength andtoughness.

polyester A broad class of polymerspossessing good moisture resistanceand electrical properties.

polyetherimide (PEI) A high-temperature thermoplastic withexcellent strength and chemicalresistance.

polyethylene (PE) A thermoplasticthat exhibits excellent dielectriccharacteristics.

polymer Any substance made ofmany repeating chemical molecules.Often used in place of plastic, rubberor elastomer.

polyphenylene sulfide (PPS) A high-temperature thermoplastic with goodsolvent resistance and flameretardation.

polypropylene A thermoplastic that issimilar to polyethylene, but has ahigher softening point (temperature).

polysulfone (PSU) A thermoplasticwith excellent water and similar fluidresistance.

polyurethane (PUR) A broad class ofpolymers that has good abrasion andchemical resistance.

polyvinyl chloride (PVC) Athermoplastic with excellent dielectricstrength and flexibility.

positive temperature coefficient(PTC) An increase in resistance thatoccurs with an increase intemperature. See “resistancetemperature detector” and“thermistor.”

potting The sealing of componentsand associated conductors with acompound to exclude moisture andcontaminants. power factor (PF) The ratio of realpower (PR) to apparent power (PA).

power loss alarm Associated withlatching limit controls, the limit controlrecognizes a power outage as a limitcondition. Manual reset is required tore-energize the output after power isrestored.

PPS See “polyphenylene sulfide.”

pre-aging A process by which athermocouple is subjected toapplication conditions that cause mostof any electromagnetic force shift(decalibration). When it is installed andcalibrated to an instrument, a pre-agedthermocouple will produce reliablereadings.

preferential oxidation Commonlycalled green rot. A phenomenonpeculiar to nickel-basedthermocouples, most often ASTM TypeK, when oxygen is limited. The limitedoxygen reacts with the more activechromium in the conductor alloy, whichchanges to chromium oxide andcreates a green scale. An increasingnickel skin is left behind, causingdecalibration. Decalibration is causedwhen the negative thermoelement ispaired against a nickel skin and notthe original homogeneous nickel-chromium alloy. Preferential oxidationwill not occur when there is anabundant supply or a total absence ofoxygen.

presentation layer (OSI Layer 6) Thesixth layer of the seven-layer OSI(Open System Interconnection)protocol model where syntax,compatibility, and encryption issuesare resolved. The Presentation Layerresides between the Application Layerand the Session Layer.

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Glossaryprimary standard An instrument thatmeets conditions required by theInternational Temperature Scale(ITS90).

probe A temperature sensor. A probemay contain a thermocouple, RTD,thermistor or integrated circuit (IC)sensor.

process alarm Warns that processvalues are outside the process alarmrange. A fixed value independent ofthe set point.

process error The differencebetween the set point and the actualprocess value.

process variable The parameter thatis controlled or measured. Typicalexamples are temperature, relativehumidity, pressure, flow, fluid level,events, etc. The high process variableis the highest value of the processrange, expressed in engineering units.The low process variable is the lowestvalue of the process range.

programmed display data Displayedinformation that gives the operator theintended process information, such asintended set point, intended alarmlimit, etc., corresponding totemperature or other engineering units.

prompt A symbol or messagedisplayed by the computer orcontroller that requests input from theuser.

proportional Output effortproportional to the error from set point.For example, if the proportional bandis 20° and the process is 10° below setpoint, the heat proportioned effort is 50percent. The lower the PB value, thehigher the gain.

proportional band (PB) A range inwhich the proportioning function of thecontrol is active. Expressed in units,degrees or percent of span. See “PID.”

proportional control A control usingonly the P (proportional) value of PIDcontrol.

protection head An enclosure thatprotects the electrical connections ofheaters or sensor probes.

protection tube A tube that protects asensor (thermocouple, RTD orthermistor) from harsh environmentalor process conditions.

psia Pounds per square inchabsolute. Pressure expressed in termsof its actual or absolute value withreference to a perfect vacuum. psia =psig + 14.7 psi (1 atmosphere). See“psig.”

psig Pounds per square inch gauge.Pressure expressed in terms of a valueread directly from installed gauges.psig = psia -14.7 psi (1 atmosphere). See “psia.”

PSU See “polysulfone.”

PTFE Chemical abbreviation forpolytetrafluoroethylene. See “Teflon®”and “TFE.”

pulse input Digital pulse signals fromdevices, such as optical encoders.

PVC See “polyvinyl chloride.”

Qquality Thermodynamic term thatindicates the relative amount of liquidpresent in saturated steam as apercent of the total weight. The qualityof steam is 100 percent minus thepercent of liquid. Dry saturated steamhas a quality of 100 percent.

Rradiation Radiant energy emitted inthe form of waves or particles. See“emissivity” and “infrared.”

radio frequency interference (RFI)Electromagnetic waves between thefrequencies of 10kHz and 300gHz thatcan affect susceptible systems byconduction through sensor or powerinput lines, and by radiation throughspace.

ramp A programmed increase in thetemperature of a set point system.

range The area between two limits inwhich a quantity or value is measured.It is usually described in terms of lowerand upper limits.

rate Anticipatory action that is basedon the rate of temperature change,and compensates to minimizeovershoot and undershoot. See“derivative.”

rate band A range in which the ratefunction of a controller is active.Expressed in multiples of theproportional band. See “PID.”

ratio A method by which the controllermeasures the flow of an uncontrolledvariable and uses a portion of it tocontrol the flow of a second variable.

recipe See “job.”

reference junction The knowntemperature point at which athermocouple or its extension wireconnects to a temperaturemeasurement instrument or controller.To prevent an error from introducingitself at this point, some instrumentswill add a compensation value to thesignal. Also called the “cold junction.”

reflection compensation mode Acontrol feature that automaticallycorrects the reading from a sensor.

reflective energy Energy from thebackground that causes an error whenan infrared sensor measures theradiant energy of a specific object. refractory metal thermocouple Athermocouple made from materialssuch as tungsten and rhenium, whichmelt above 1935°C (3515°F). Theseare non-ASTM types C, D and G. relative thermal index (RTI) A long-term heat aging test used byUnderwriter’s Laboratories (UL®) todetermine the maximum applicationtemperature for plastics.

relay A switching device.

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Glossaryremote A controller that receives itsset point signal from another devicecalled the master.

remote set point A signal fromanother device that indicates the setpoint for the process.

repeatability The ability to provide thesame output or reading underrepeated, identical conditions. See“stability.”

reset Control action that automaticallyeliminates offset, or droop, betweenset point and actual processtemperature. Also see “integral.”

reset windup inhibit See “anti-resetwind-up.”

resistance Opposition to the flow ofelectric current, measured in ohms.See “ohms.”

resistance temperaturecharacteristic The characteristicchange in a sensor’s resistance whenexposed to a change in temperature.See “positive temperature coefficient”and “negative temperature coefficient.”

resistance temperature detector(RTD) A sensor that uses theresistance temperature characteristicto measure temperature. There are twobasic types of RTDs: the wire RTD,which is usually made of platinum, andthe thermistor, which is made of asemiconductor material. The wire RTDis a positive temperature coefficientsensor only, while the thermistor canhave either a negative or positivetemperature coefficient.

resistive loads All loads that limit theflow of electric current. With pureresistive loads, voltage and current arein phase.

resolution An expression of thesmallest input change unit detectableat a system output.

response time (time constant) 1) Thetime required by a sensor to reach63.2 percent of a temperature stepchange under a specified set ofconditions. Five time constants arerequired for the sensor to stabilize at100 percent of the step change value.2) With infrared temperature sensing,the time required for a sensor to reach95 percent of a step change. This isknown as the time constant timesthree. The overall system responsetime is the sum of the time constants ofeach component.

retransmit output An analog outputsignal that may be scaled to representthe process value or set point value.

reverse action An output controlaction in which an increase in theprocess variable causes a decrease inthe output. Heating applicationsusually use reverse action.

RFI See “radio frequencyinterference.”

rhenium (Re) A metallic element that,when added to tungsten, forms analloy with better ductility and highertemperature strength than tungstenalone.

rhodium (Rh) A metallic elementinside the platinum group that, whenadded to pure platinum, forms an alloywith reduced ductility and better hightemperature strength than platinumalone.

router A device that connects onecomputer local area network (LAN) toanother using ICMP (Internet ControlMessage Protocol), part of IP (InternetProtocol), to communicate with otherrouters, and to determine optimumdata paths.

RTD See “resistance temperaturedetector.”

RTI See “relative thermal index.”

rubber insulation A generaldesignation for thermosettingelastomers, such as natural andsynthetic rubbers, neoprene,Hypalon®, and butyl rubber. They areused to insulate wire conductors.Hypalon® is a registered trademark ofthe E.I. duPont de Nemours &Company.

SSAE See “Society of AutomotiveEngineers.”

safety limit An automatic limitintended for use in applications wherean over-temperature fault may cause afire or pose other safety concerns.

SAMA See “Scientific ApparatusMakers Association.”

saturation pressure The pressure ona liquid when it boils at a giventemperature. Both the saturated liquidand saturated vapor phases can existat this time.

saturation temperature The boilingtemperature of a liquid at its existingpressure.

scfm Standard volumetric flow rate incubic feet per minute. A measure ofthe flow rate of gases and vaporsunder standard conditions of 15°C(60°F) and standard atmosphericpressure.

Scientific Apparatus MakersAssociation (SAMA) An associationthat sets standards for platinum, nickeland copper resistance elements(RTDs).

SCR See “silicon controlled rectifier.”

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Glossaryscreen printing A printing methodthat uses a photographic process tocreate an image on a fine screen, andthen transfers that image to anothersurface with a squeegee forcing ink orother viscous material through themesh of the screen. Watlow usesscreen printing in both traditionalproduct labeling and in thick filmmanufacturing.

secondary standard A measurementdevice that refers to a primarystandard.

Seebeck coefficient The rate ofchange (derivative) of thermal EMF(voltage) with respect to temperature.Expressed as millivolts per degree.

Seebeck effect When a circuit isformed with a junction of two dissimilarmetals and the junctions at each endare held at different temperatures, acurrent will flow in the circuit.

Seebeck EMF The net thermalelectromotive force (EMF) in athermocouple under conditions of zerocurrent.

semiconductor Any material thatexhibits a degree of electricalconductivity that falls between that ofconductors and dielectrics.

serial communications A method oftransmitting information betweendevices by sending all bits seriallyover a single communication channel.

series circuit A circuit configurationin which a single current path isarranged among all components.

server A device or computer on anetwork that serves or delivers networkresources, such as a file server,database server, print server or webserver.

serving The process by whichmetallic or nonmetallic filaments orfibers are woven around a wireconductor to produce electricalinsulation, shielding or improvedabrasion resistance. See “braid.”

Session Layer (OSI Layer 5) The fifthlayer of the seven-layer OSI (OpenSystem Interconnection) protocolmodel that starts, stops and managesconnections between applications.The Session Layer resides betweenthe Presentation Layer and theTransport Layer.

set point The desired valueprogrammed into a controller. Forexample, the temperature at which asystem is to be maintained.

setpot A potentiometer used to adjustcontroller set point temperature.

setting accuracy Closeness betweenthe value established by an inputdevice, such as a dial, and the desiredvalue. Usually expressed as a percentof span or number of digits.

SFPM Standard flow velocity in feetper minute. For gas flow, it is evaluatedusing the SCFM (standard cubic feetper minute) divided by the flow area.

sfpm Standard flow velocity in feetper minute. Gas flow is calculatedusing scfm divided by the flow area.

shape factor The amount of energy atarget object receives, relative to thesize of the heater and its distance fromthe object.

sheath thermocouple A mineral-insulated thermocouple that has anouter metal sheath. It is usually madefrom mineral-insulated thermocouplecable.

shield A metallic foil or braided wirelayer surrounding conductors that isdesigned to prevent electrostatic orelectromagnetic interference fromexternal sources.

shield coverage See “shieldpercentage.”

shield effectiveness The relativeability of a shield material to screeninterference. Shield effectiveness isoften confused with shield percentage.

shield percentage The area of acircuit or cable that is covered by ashielding material, expressed as apercentage.

shunt In an electrical circuit, a lowresistance connection between twopoints that forms an alternate path forsome of the current. Dielectricmaterials lose resistance attemperatures above their operatingrange. This condition can causeshunting of the sensor’s signal,causing an error in the reading.

SI Systems Internationale. The systemof standard metric units.

signal Any electrical transmittancethat conveys information.

silicon A tetravalend nonmetallicelement.

silicon controlled rectifier (SCR) Asolid-state device, or thyristor, with nomoving parts, that is used in pairs tocontrol ac voltages within one cycle.SCRs control voltage from a powersource to the load by burst firing (alsocalled zero-cross firing) or phaseangle firing. See “burst fire.”

silicone A thermosetting elastomerthat is made of silicone and oxygen,and noted for high heat resistance.

silicone rubber Rubber that is madefrom silicone elastomers and noted forits retention of flexibility, resilience andtensile strength.

slidewire feedback A method ofcontrolling the position of a valve.using a potentiometer. The resistanceindicates the valve position.

SMTP Simple Mail Transfer Protocol.A protocol that enables e-mail serversand clients to send e-mail.

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GlossarySNMP Simple Network ManagementProtocol. Protocols for managingcomplex networks. SNMP exists at thePresentation (Layer 6) and Application(Layer 7) layers of the seven-layerOpen System Interconnection (OSI)model, from standard ISO/IEC(International Organization forStandardization/InternationalElectrotechnical Commission) 7498-1.

SNMP agent A means for a networkadministrator to communicate with anobject within a specific device on anetwork.

SNMP manager A networkadministrator’s interface for performingnetwork management tasks on anetwork’s Simple NetworkManagement Protocol layers.

soaking In heat treating, the practiceof immersing an object in a heatedenvironment so it can complete adesired metallurgical change at aspecific temperature.

Society of Automotive Engineers(SAE) A society that establishesstandards for the transportationindustries (automotive, marine andaviation), including the system ofEnglish units (pounds, feet, gallons,etc.).

soft start A method of using phase-angle SCR control to graduallyincrease the output power over aperiod of several seconds. Soft startsare used for heaters that have a lowelectrical resistance when they arecold, or for limiting in-rush current toinductive loads.

software Instructions that enable acomputing device 1) to function, as inan operating system , or 2) to performspecific tasks, as in applications.These instructions are typically storedin some type of memory media.

solid-state relay (SSR) A switchingdevice with no moving parts thatcompletes or interrupts a circuitelectrically.

span The difference between thelower and upper limits of a rangeexpressed in the same units as therange. See “range.”

spark test A high voltage, lowamperage test that detects insulationdefects in wire and cable.

specific gravity (sp. gr.) Densityrelative to the density of water, which isgiven the arbitrary value of one at 0°C.See “density.”

specific heat capacity The quantity ofheat (in joules or Btus) necessary toraise the temperature of one kilogram(or pound) of substance through 1Kelvin. In most materials, specific heatcapacity varies with changes intemperature and material state.

specific volume The inverse ofdensity, expressed in units of cubicfeet per pound or cubic meters perkilogram.

spectral filter A filter that restricts theelectromagnetic spectrum to a specificbandwidth, such as four to eightmicrons infrared radiation.

spectral response band The regionof the infrared portion of theelectromagnetic spectrum over whichan infrared sensor processes a signal.Infrared sensors that operate at shorterwavelengths are designed for highertemperatures.

spot size See “field of view.”

spread In heat/cool applications, thedifference between heat and cool. Alsoknown as process dead band. See“dead band.”

SSR See “solid state relay.”

stability The ability of a device tomaintain a constant output with theapplication of a constant input.

standard A set value or referencepoint from which measurements orcalibrations are made.

standard wire error The level ofdeviation from established standards.Usually expressed in terms of ±°C orpercent. Also known as standardtolerances.

subnet Part of a TCP/IP network thatshares the same IP address prefix.Networks are divided into subnets toincrease performance and security.

superheat Heating of a gas or vaporto a temperature well above its drysaturation temperature. This term willbe encountered frequently whenworking with steam. Thesetemperatures, coupled with thetabulated enthalpy values, provide asimple means of calculating the powerneeded for superheating.

surge current A short duration rush ofcurrent that occurs when power is firstapplied to capacitive, inductive ortemperature dependent resistiveloads, such as tungsten or siliconcarbide heating elements. It alsooccurs when inductive loads are de-energized. Surge currents usually lastno more than several cycles.

swage Uniform compaction processthat decreases the diameter andincreases the length of a cylinder. Thiscompaction process used in cartridgeheater and sensor manufacturing,creates higher thermal conductivity(better heat transfer) and greaterdielectric strength (longer life). The unitcan be swaged multiple times, knownas double swaging.

switch 1) A device, either electrical ormechanical, used to open or close anelectrical circuit. 2) A computerprogramming technique that willchange a selection from one state toanother. 3) A telephone interface thatconnects callers. 4) A network routingdevice that provides numbered nodes,one for each connected device.

switching differential See“hysteresis.”

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Glossaryswitching sensitivity In on-offcontrol, the temperature changenecessary to change the output fromfull on to full off. See “hysteresis.”

Systems Internationale (SI) Thesystem of standard metric units.

TTCP Transmission Control Protocol.One of two primary protocols thatdistinct Internet hosts use to establisha connection and exchange data whileensuring that data packets arereceived in the same order as theywere sent. TCP is a session-basedtransport layer protocol defined by theIETF. See “IP” and “TCP/IP.”

TCP/IP Transmission ControlProtocol/Internet Protocol. The twoprimary protocols used to connecthosts and exchange data on theInternet.

TD Timed derivative. The derivativefunction.

Teflon® A registered trademark of E.I.duPont de Nemours & Company,covering a family of fluorocarbonmaterials that includes FEP, PFA andPTFE.

Tefzel® (ETFE) Fluoropolymer material,ethylene tetrafluoroethylene, withexcellent mechanical properties,particularly important in wire and cableapplications. Tefzel® is a registeredtrademark of the E.I. duPont deNemours & Company.

Telecommunication IndustryAssociation (TIA) A trade group thatsets standards for thetelecommunications industries.

temperature calibration point Atemperature at which the output of asensor is compared against astandard.

temperature limit switch FactoryMutual (FM) Standard 3545. See “limitcontrol.”

temperature, ambient Thetemperature of the air or other mediumthat surrounds the components of athermal system.

tera (T) A prefix meaning 1012 (onetrillion in the US).

TFE A common short handabbreviation for PTFE,polytetrafluoroethylene, or Teflon®.

thermal conductivity The quantity ofheat transmitted by conductionthrough a body per unit area, per unittime, per unit thickness for atemperature difference of 1 Kelvin.This value changes with temperature inmost materials and must be evaluatedfor conditions given. Expressed inBtu/hr-ft-°F or Watts/meter-°C.

thermal EMF The ability of athermocouple to produce a voltagethat increases or decreases inproportion to its change intemperature.

thermal expansion An increase in thesize of a material that is caused by anincrease in temperature. Expressed asthe number of inches/inch/°F orcm/cm/°C per reference length.

thermal gradient The distribution ofdifferential temperatures through abody or across a surface.

thermal lag The delay in thedistribution of heat energy throughouta system. Thermal lag can causeprocess temperature instability.

thermal shunt A condition in whichthe mass of the sensor absorbs aportion of the heat being measured,which results in an erroneous reading.

thermal system A regulatedenvironment that consists of a heatsource, heat transfer medium or load,sensing device and a controlinstrument.

thermistor A temperature sensingdevice made of a semiconductormaterial that exhibits a large change inresistance for a small change intemperature. Thermistors usually havenegative temperature coefficients,although they are also available withpositive temperature coefficients.

thermocouple (T/C) A temperaturesensing device made by joining twodissimilar metals. This junctionproduces an electrical voltage inproportion to the difference intemperature between the hot junction(sensing junction) and the lead wireconnection to the instrument (coldjunction).

thermocouple aging or aging rangeA positive shift in electromotive force(EMF) in nickel-based thermocouplealloys that is caused by a temperaturegradient along the thermocoupleelements. Factors that cause EMF shiftare the measured temperature, theprevious thermal history of theelement, the amount of time spent atthe aging temperature and the amountof the element subjected to the agingtemperature. Different thermocoupletypes age differently under differentapplication conditions.

thermocouple break protection Theability of a control to detect a break inthe thermocouple circuit and take apredetermined action.

thermocouple extension wire A pairof wires connecting a thermocouplesensor to its reference junction orinstrumentation. The electromotiveforce (EMF) characteristics of theextension wire must be similar to theEMF characteristics of thethermocouple.

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Glossarythermocouple junction The pointwhere the two dissimilar metalconductors join. In a typicalthermocouple circuit, there is ameasuring junction and a referencejunction. See “junction,” “measuringjunction” and “reference junction.”

thermocouple pre-aging See “pre-aging.”

thermocouple type A particularcombination of metallic elementsand/or alloys that make up theconductors of a thermocouple, anddefines their EMF output relative toabsolute temperature. ASTMdesignated types include: B, E, J, K,N, R, S and T. Non-ASTM typesinclude: C, D and G (tungsten basedthermocouples) and Pt 2.

thermocouple, heat treating Athermocouple that is appropriate forthe temperature range andatmospheres used in heat treating.Heat treating is a process that altersthe physical properties of a metal byheating and cooling at specific ratechanges, and by introducing chemicalatmospheres.

thermopile An arrangement ofthermocouples in a series withalternate junctions at the measuringtemperature and the referencetemperature. This arrangementamplifies the thermoelectric voltage.Thermopiles are usually used ininfrared detectors in radiationpyrometry.

thermopolymer technology Thetechnology that applies heatedplastics to applications.

thermoset A material that undergoesa chemical reaction and is cured or setwhen subjected to heat. An example isbakelite. Thermosetting also applies tovulcanizing, as with rubber andneoprene.

thermowell A tube with a closed endthat is designed to protect temperaturesensors from hostile environments. See“protection tube.”

Thompson Effect When a currentflows through a conductor within athermal gradient, a reversibleabsorption or evolution of heat occursin the conductor at the gradientboundaries.

three-mode control Proportioningcontrol with integral (reset) andderivative (rate). Also see “PID.”

TI Integral term.

TIA See “TelecommunicationsIndustry Association.”

time proportioning control A methodof controlling power by varying the on-off duty cycle of an output. Thisvariance is proportional to thedifference between the set point andthe actual process temperature.

Tophel® A thermocouple alloy that ismade of 90 percent nickel and 10percent chromium. It is used in thepositive conductors of ASTM Type Eand K thermocouples. Tophel® is aregistered trademark of CarpenterTechnology.

transducer A device that receivesenergy in one form and retransmits it inanother form. For example, athermocouple transforms heat energyinput into a voltage output.

transient A surge in electrical current,usually of short duration. Transientscan damage or interfere with theproper operation of electronictemperature and power controllers.

transmitter A device that transmitstemperature data from either athermocouple or a resistancetemperature detector (RTD) by way ofa two-wire loop. The loop has anexternal power supply. The transmitteracts as a variable resistor with respectto its input signal. Transmitters aredesirable when long lead or extensionwires produce unacceptable signaldegradation.

Transport Layer (OSI Layer 4) Thefourth layer of the seven-layer OSI(Open System Interconnection)protocol model that handles datatransfer, flow control and errorrecovery between communicatinghosts. The Transport Layer residesbetween the Session Layer and theNetwork Layer.

triac A solid-state device thatswitches alternating current.

tribology The science or study ofsurface friction.

triple point A thermodynamic state inwhich the gas, liquid and solid phasesall occur in equilibrium. For water, thetriple point is 0.01°C at standardatmospheric pressure.

tungsten (W) An element that is usedas the positive conductor in a Type Gthermocouple, which is made oftungsten/tungsten 26 percent rhenium(W/W26Re). Type G is not an ASTMsymbol.

tungsten 25 percent rhenium Thethermocouple alloy that is used as thenegative conductor in a Type Dthermocouple, which is made oftungsten 3 percent rhenium/tungsten25 percent rhenium thermocouple(W3Re/W25Re). Type D is not anASTM symbol.

tungsten 26 percent rhenium Thethermocouple alloy that is used as thenegative conductor in both the Type Gthermocouple, which is made oftungsten/tungsten 26 percent rhenium(W/W26Re), and the Type Cthermocouple, which is made oftungsten 5 percent/tungsten 26percent rhenium (W5Re/W26Re).Types G and C are not ASTM symbols.

tungsten 3 percent rhenium Thethermocouple alloy that is used as thepositive conductor in a Type Dthermocouple, which is made oftungsten 3 percent rhenium/tungsten25 percent rhenium (W3Re/W25Re).Type D is not an ASTM symbol.

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Glossarytungsten 5 percent rhenium Thethermocouple alloy that is used as thepositive conductor in a Type Cthermocouple, which is made oftungsten percent rhenium/tungsten 26percent rhenium (W5Re/W26Re). TypeC is not an ASTM symbol.

tungsten lamp The technology usedby the standard incandescent lightbulb, in place since 1911, with atungsten metal filament surrounded byan inert gas or a vacuum. Tungstenhas a 16:1 hot to cold resistance ratio,that is, the filament has 16 time higherresistance at its hot operatingtemperature than at cooler ambient.

turnkey A selling feature describing acomplete and ready to use system,one similar to simply turning the doorkey of a ready-to-live-in home. Watlowoffers turnkey solutions with cast-inand thick film heaters.

twisted pair Two insulatedconductors that are twisted together.An effective method of duplexing andreducing electromagnetic interference(EMI).

UUDP User Datagram Protocol. Aconnectionless protocol that runs ontop of IP networks as UDP/IP. Hostscan broadcast messages via UDP/IPwithout establishing connections withthe receivers. Datagrams are packets,pieces of messages. UDP is asessionless transport layer protocoldefined by the IETF.

UL® The registered trademark andabbreviation for the Underwriter’sLaboratories, Inc. An independenttesting laboratory that establishescommercial and industrial standards,and tests and certifies products in theUnited States.

ultraviolet The portion of theelectromagnetic spectrum that is justbeyond the violet in the visiblespectrum. Ultraviolet light can degrademany insulation materials.

undershoot The amount by which aprocess variable falls below the setpoint before it stabilizes.

ungrounded junction See “isolatedjunction.”

uninsulated Without thermalinsulation; without electrical insulation(bare wire).

union A pipe fitting that joinsextension pipes, without regard to theirthread orientation.

upscale break protection A form ofbreak detection for burned-outthermocouples. It signals the operatorthat the thermocouple has burned out.

USB Universal Serial Bus. An externalbus standard for connecting as manyas 127 peripheral devices tocomputers with data transfer rates ofup to 12 Mbps (million bits persecond). USB is likely to supercedeserial and parallel ports because of itsspeed and "hot swappable" (unplugand plug in with power on) feature.

Vvacuum braze A process to joinmetals or alloys with heat in theabsence of atmosphere, in a vacuumchamber or furnace, for example.

value The quantitative measure of asignal or variable.

VDE Abbreviation for VerbandDeutscher Elektrotechniler, anindependent German testing andcertification institute concerned withthe safety of electrical products.Authorizes use of the VDE Mark.

viscosity The resistance of fluid tosheering forces (flow). High viscosityindicates a tendency for a fluid to flowor move slowly. The viscosity of fluidsdecreases as their temperaturesincrease. Heating gases will increasetheir absolute viscosity.

VOC 1) Volatile OrganicCompound(s). Carbon-based organiccompounds that evaporate quickly.Watlow's thick film heaters do notcontain harmful volatile organiccompounds, such as hydrocarbons,ammonia fluorine, hydrogen sulfide orsulfur dioxide. 2) Voice of theCustomer; APICS (The EducationalSociety for Resource Management).

volt (V) The unit of measure forelectrical potential, voltage orelectromotive force (EMF). See“voltage.”

volt amperes (VA) A measurement ofapparent power. The product ofvoltage and current in a reactivecircuit. V I = VA, where V is volts and Iis current in amperes. The term watt isused for real power.

voltage (V) The difference in electricalpotential between two points in acircuit. It’s the push or pressure behindcurrent flow through a circuit. One volt(V) is the difference in potentialrequired to move one coulomb ofcharge between two points in a circuit,consuming one joule of energy. Inother words, one volt (V) is equal toone ampere of current (I) flowingthrough one ohm of resistance (R), or V = IR.

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GlossaryW - Xwatt (W) A measurement of realpower. The product of voltage andcurrent in a resistive circuit. VI = P,where V is volts, I is current in amperesand P is power in watts.

watt density The watts of powerproduced per unit of surface area of aheater. Watt density indicates thepotential for a surface to transmit heatenergy and is expressed in W/in2 orW/cm2. This value is used to expressheating element ratings and surfaceheat loss factors.

WCAD™ A computer-based version ofa power calculations tool published byWatlow Polymer Technologies.

web server A device with an IPaddress and running server softwareto make it capable of serving webpages to a network or to the Internet.A web server may also have a domainname.

wire size The specification and use ofproper wire gauge for the load sizeand its distance from the control. Wiresizing is of prime importance to outputwiring. Refer to the National ElectricalCode (NEC) and local codes for wiresizing guidelines. See “American WireGauge” and “B & S Gauge.”

working standard A measurementdevice that refers to a secondarystandard.

WPT Watlow Polymer Technologies.A Watlow division that manufacturesheated plastics.

XML eXtensible Markup Language. A document markup language definedby the Worldwide Web Consortium(WC3) as a subset of SGML (StandardGeneralized Markup Language), and aweb-friendly document descriptiontool. XML provides for customized tagsthat enable data sharing betweensystems, applications andorganizations.

Zzero cross Action that providesoutput switching only at or near thezero-voltage crossing points of the AC sine wave. See “burst fire.”

zero switching See “zero cross.”