Table of Contents...Table of Contents 3 (775) 674-5100 l (800)W257-3526 l FAX (775) 674-5111 l E-mail: [email protected] NTC Thermistor Probes - CPWSeries 4-7 Custom Epoxy

Table of Contents

www.selcoproducts.com 3

(775) 674-5100 l (800) 257-3526 l FAX (775) 674-5111 l E-mail: [email protected]

Custom NTC Thermistor Probes - CP Series 4-7

Custom Epoxy NTC Thermistors - CS Series 8-9

Tiny NTC Thermistor Probes - LS Series 10

Miniature NTC Thermistor Probes - LSMN Mini Series 11

Micro NTC Thermistor Probes - LSMC Micro Series 12

Interchangeable NTC Thermistors - IN Series 13-14

Diode Type NTC Thermistors - DT Series 15

Radial Glass Bead Thermistors - RG Series 16

Point Matched NTC Thermistors - PM Series 17-18

Thin Film NTC Thermistors - TF Series 19

Insulated Lead Epoxy Thermistors - TS Series 20

Short Lead NTC Epoxy Thermistors - HP Series 21

Long Lead NTC Epoxy Thermistors - HT Series 22

Technical Notes 23

Thermistor Definition

Manufacturing Process

Resistance - Temperature (R-T) Curves and NTC

Thermal Time Constant

Dissipation Constant

Voltage/Current Requirements

Beta

Steinhart-Hart Equation

Temperature Rating

Stability

Resistance - Temperature Tables 24-25

Application Notes 26-28

Custom NTC Thermistor ProbesCP Series

www.selcoproducts.com4


Temperature Sensor Applications

Household Appliances Medical Electronics Industrial Electronicsl Dryers l Infant Incubators l Fire Detectorsl Heaters l Blood Analysis Equipment l Solar Collectorl Toasters l Skin Temperature Monitors l HVAC Equipmentl Refrigerators l Internal Temperature Sensor l Water Purificationl Coffee Makers l Respiration Rate Measurement l Plastic Laminatingl Air Conditioners l Electronic Clinical Thermometer l Vending Machinesl Washing Machines l Welding Equipment

l Weather MonitoringOther Consumer Electronics Automotive l Industrial Process Controll Cooling Fan l Hybrid Battery Sensor l Oceanography Monitoringl Battery Pack l Water / Oil Tank Sensor l Fruit Transportation Process Controll Wireless Card l Automatic Climate Controll Audio Amplifiers l Outside Air Temperature Sensorl Cellular Telephones l Engine Block Temperature Sensorl Pool and Spa Control

SPECIFICATIONS




FEATURESl Custom NTC thermistor probe assembliesl Interchangeable or tolerance based assembliesl Assemblies manufactured to meet your applicationl RoHS Compliant

CP Series probes are designed to meet your specificapplication requirements. Custom probe designs havevirtually unlimited options available. Their value-addedfeatures significantly reduce your labor costs.

Contact our applications engineering team for assistance to design, quote, and manufacture your custom NTCthermistor probe assembly.

Temperature rating/ CP Series probes using an interchangeablerecommended operating IN Series or a tolerance based PM, Series

Point matched thermistor may beintermittently cycled from -50ºC to 150ºC. Optimum stability is achievedwhen these thermistors are continuouslyoperated at or below 125ºC.

Note: CP Series probes using a 250ºC rated DT Series can be intermittentlyoperated from -50ºC to 250ºC with optimum stability when operated at or below200ºC. A 300ºC rated DT or RG Series can be intermittently operated from-50ºC to 300ºC with optimum stability when operated at or below 260ºC.

CP Series probes using interchangeable DT Series thermistors: 250ºC rated: Optimum stability is achieved when continuously operated at180ºC or below. 300ºC rated: Optimum stability is achieved when continuously operated at230ºC or below.

Resistance at 25°C See CP Series ordering map - page 7

R-T curves CP Series thermistors probes are available in all R-T curve materials.Detailed curve material information onpages 24-25.

Accuracies ±0.05°C, ±0.10°C, ±0.2°C, ±0.5°C,±1.00°C

Accuracy temp ranges See CP Series ordering map - page 7

Tolerances at 25°C ±1.0%, ±2.0%, ±3.0%, ±5.0%

Dissipation constant, thermal time constant and maximum powerrating specifications vary depending on the discrete thermistorseries used in the probe assembly.

Wire Styles Configuration Gauge Insulation

Single Conductor

Jacketed

Zipcord

Twisted

18-32

22-30

22-24

22-26

PVC, XLPE Teflon

PVC, Etched Teflon

PVC

PVC, Teflon

The following are a few examples of the unlimited choices for the combination of wire and probe housings

Note: Selco can provide options such as corrosion resistant housings, plastic molded or over-molded housings, high pressure (PSI) rated housings, and moistureresistant thermistor probe assemblies. Contact Selco for more information.




Housings Type Material

Threaded NPTfitting round,

close-end tube

Brass316 Stainless Steel

Flat closed-ended PVC, Stainless Steel,Brass, Overmold

Rounded, closed-end cup Delrin, Stainless Steel,Brass, Overmold

Ring lug terminal bolt Steel, Copper

Ring lug terminal bolt Steel, Copper

Probe304 Stainless Steel,316 Stainless Steel,

Brass, Aluminum, Plastic

Threaded NPT plug

304 Stainless Steel,316 Stainless Steel,Brass, Aluminum, Plastic, Overmold

Open-end tube304 Stainless Steel,316 Stainless Steel,


Expanded Probe304 Stainless Steel,316 Stainless Steel,


Tapered-end Probe304 Stainless Steel,316 Stainless Steel,


Flange Mount Probe304 Stainless Steel,316 Stainless Steel,


The following are a few examples of the unlimited choices for the combination of wire and probe housings

Custom NTC Thermistor ProbesCP Series - Ordering Map



CP - - - X X X X

Resistance at 25°C0300 = 300 Ohms001K = 1K Ohms005K = 5K Ohms006K = 6K Ohms010K = 10K Ohms100K = 100K Ohms2252 = 2,252 Ohms1MEG = 1 Million OhmsX = Special base resistance value

IN Series Interchangeable AccuraciesA = ±1.0°C D = ±0.1°CB = ±0.5°C E = ±0.05°CC = ±0.2°C X = Special

DT Series Interchangeable AccuracyC = ±0.2°C

DT and RG Series Tolerance at 25°CPM Series Tolerances at Point Matched Temperature

1 = ±1% 5 = ±5%2 = ±2% 0 = ±10%3 = ±3% X = letter or digit assigned for specials

IN Series Accuracy Temperature Ranges1 = 20°C to 45°C 6 = -40°C to 40°C2 = -20°C to 50°C 7 = +50°C to 125°C3 = 0°C to 70°C 8 = 0°C to 50°C4 = 0°C to 100°C 9 = -20°C to 125°C5 = +20°C to 90°C X = Specials

PM Series Point Matched TemperaturesA = -20°C D = 37°CB = 0°C E = 70°CC = 25°C F = 100°CX = Specials

ORDERING MAP

l Lead lengthl Wire gauge sizel Solid or stranded wirel Probe type descriptionl Connectors if required (Molex, TE, or other)l Blunt or stripped end and length of stripped wirel Insulation material (Isomid, Kynar, Nylon, PVC, Teflon, etc.)

TO ORDER SPECIFY ALL ITEMS BELOW

XXXX = System file number assigned

Note: Other thermistor base resistance values, thermistor curves or Beta values, or tolerances may be available. Please contactSelco Products.

R-T CurveA = Curve A E = Curve E H = Curve HB = Curve B F = Curve F K = Curve KC = Curve C G = Curve G P = Curve PD = Curve D X = New letter assigned for special curve

DT Series Interchangeable Accuracy Temp. Range3 = 0°C to 70°C

Note: 300°C rated DT Series thermistors may beidentified as an option in the XXXX Special partnumber section of the catalog number.

R-T Tables are listed on pages 24-25

Custom Epoxy NTC ThermistorsCS Series



FEATURESl Epoxy encapsulated thermistors with insulated leadsl Application specific custom thermistors manufacturedl Interchangeable or tolerance based assembliesl RoHS Compliant

CS Series thermistors are designed to meet your specific application requirements. For “turn-key” solutions, their value-addedfeatures can significantly reduce your labor costs. Contact your applications engineering personnel for assistance to design,quote and manufacture your custom CS thermistor.

SPECIFICATIONS

Temperature rating/ CS Series probes using an recommended operating interchangeable IN Series or a toleranceranges based PM Series thermistor may be

intermittently cycled from -50°C to 150°C. Optimum stability is achieved when these thermistors are continuouslyoperated at or below 125°C

Resistance at 25°C See CS Series ordering map - page 9

R-T curves CS Series thermistors are available in all R-T curve materials. R-T tables are available on pages 24-25.

Accuracies ±0.05°C, ±0.1°C, ±0.2°C, ±0.5°C±1.0°C

Accuracy temp ranges See CS Series ordering map - page 9

Tolerances at 25°C ±1%, ±2%, ±3%, ±5%, ±10%

Dissipation constant Varies depending on the discrete series thermistor series used in the probe assembly

Thermal time constant Typically 10.0 to 15.0 seconds in still airTypically 0.75 to 2.0 seconds in stirred oil

Maximum power rating 30 mW at 25°C to 1 mW at 100°C Custom options Various lead AWGs, insulation

materials, lead lengths and connectors

Note: Several CS Series Thermistors are available with UL Component Recognition. Please contact Selco Products for availability.

CS - - - X X X X

Custom Epoxy NTC ThermistorsCS Series - Ordering Map



R-T CurveA = Curve A E = Curve E H = Curve HB = Curve B F = Curve F K = Curve KC = Curve C G = Curve G P = Curve PD = Curve D X = New letter assigned for special curve

Resistance at 25°C0300 = 300 Ohms001K = 1K Ohms005K = 5K Ohms006K = 6K Ohms010K = 10K Ohms100K = 100K Ohms2252 = 2,252 Ohms1MEG = 1 Million OhmsX = Special base resistance value

IN Series Interchangeable AccuraciesA = ±1.0°C D = ±0.1°CB = ±0.5°C E = ±0.05°CC = ±0.2°C X = Special

PM Series at Point Matched Temperatures1 = ±1% 5 = ±5%2 = ±2% 0 = ±10%3 = ±3% X = Special

IN Series Accuracy Temperature Ranges1 = +20°C to 45°C 6 = -40°C to 40°C2 = -20°C to 50°C 7 = +50°C to 125°C3 = 0°C to 70°C 8 = 0°C to 50°C4 = 0°C to 100°C 9 = -20°C to 125°C5 = +20°C to 90°C X = Special

PM Series Point Matched TemperaturesA = -20°C E = 70°CB = 0°C F = 100°CC = 25°C X = SpecialD = 37°C

ORDERING MAP

l Lead wire lengthl Wire gauge sizel Solid or stranded wirel Connectors if required (Molex, TE, or other)l Blunt or stripped end and length of stripped wirel Insulation material (Isomid, Kynar, Nylon, PVC, Teflon, etc.)

TO ORDER SPECIFY ALL ITEMS BELOW

XXXX = System file number assigned

Note: Other thermistor base resistance values, thermistor curves or Beta values, or tolerances may be available.Please contact Selco Products.

Tiny NTC Thermistor ProbesLS Series 0.078” (1 .98) probe diameter



.078” (1.98) Max.

.375” (9.5)Max.

AWG 28 Kynar Insulation

Epoxy filled PVC cup

FEATURESl Interchangeable accuraciesl Moisture coating optionall Quick Responsel RoHS Compliant

These LS series thermistors are precision thermistor assemblies andare an excellent choice for all types of applications. They are also veryuseful in applications where space is at a premium.

LS400 Series 2252 Ohms at 25°C “A” Curve

.078” (1.98) Max.

.375” (9.5)Max.

AWG 30 Kynar Insulation

Epoxy filled PVC cup

LS700 Series “A” or “B” Curve

Other values and curves available. Detailed values and curve informationon pages 24-25.

SPECIFICATIONS

Temperature rating/ LS Series thermistors may be recommended operating intermittently cycled at temperaturesranges from -50°C to 150°C. Optimum stability

is achieved when thermistors areoperated at or below 125°C.

Curves/Betas (25/85) LS Series is manufactured with A curve (3977K) or B curve (3942K). Detailed curve material information on pages 24-25.

Accuracies ±0.1°C, ±0.2°C, ±0.5°C, ±1.0°CAccuracy temp range 0°C to 70°CTolerances at 25°C ±1%, ±2%, ±3%, ±5% Dissipation constant 2.5 mW/°C in still air

13.0 mW/°C in stirred oilThermal time constant Typically 15 seconds in still air

Typically 1.25 seconds in stirred oil

Maximum power rating 10 mW at 25°C to 3.25 mW at 100°C

L S 4 0 0 A

WireGauge#28AWG

R-T CurveA = A Curve

Resistance at 25°C2252 = 2,252 Ohms

Tolerancesat 25°C1 = ±1%2 = ±2%3 = ±3%5 = ±5%

Overall LengthExample04 = 4.0”

L S 7 0 0

WireGauge#30AWG

R-T CurveA = A CurveB = B Curve

Resistance at 25°C006K = 6,000 Ohms030K = 30,000 Ohms100K = 100,000 Ohms

Overall LengthExample

10 = 10.0”

ORDERING MAPS

Special Options

Special Options

Contact Selco Products for your special requirements.

Accuraciesover 0°C to

70°CA = ±1.0°CB = ±0.5°CC = ±0.2°CD = ±0.1°C

Tolerancesat 25°C1 = ±1%2 = ±2%3 = ±3%5 = ±5%


70°CA = ±1.0°CB = ±0.5°CC = ±0.2°CD = ±0.1°C

Note: Other accuracy temperatureranges available upon request. Selcomay be able to terminate connectors tothe custom assemblies.

Miniature NTC Thermistor ProbesLSMN Series 0.035” (0 .89) and 0.055” (1 .40) probe diameters



.035” (.89) Max.

.250” (6.35)Nominal

AWG 32 Poly/Nylon

Epoxy filled polyimide tube

FEATURESl Interchangeable accuraciesl Quick responsel Moisture coating optional l RoHS CompliantThese tiny thermistors can be used in applications that require fast response and small size. They feature interchangeable accuracies over 0°C to 70°C.

LSMN 400 or 700 Series400: 2252 Ohms at 25°C “A” Curve700: “A” or “B” Curves

.055” (1.4) Max.

.125”-.375” (3.17-9.5) Typical

AWG 28 Kynar InsulationEpoxy filled polyimide tube

LSMN 400 Series2252 Ohms at 25°C “A” Curve

Other base resistances may be available - Contact Selco. Detailed R-T tableinformation can be found on pages 24-25.

SPECIFICATIONS

Temperature rating/ LSMN Series thermistors may be recommended operating intermittently cycled at temperaturesranges from -50°C to 150°C. Optimum stability

is achieved when thermistors areoperated at or below 125°C.

Curves/Betas (25/85) A curve (3977K) or B curve (3942K)Detailed curve material information on pages 24-25.

Accuracies ±0.1°C, ±0.2°C, ±0.5°C, ±1.0°CAccuracy temp range 0°C to 70°CTolerances at 25°C ±1%, ±2% , ±3%, ±5%Dissipation constant 1.5 mW/°C in still air

10.0 mW/°C in stirred oilThermal time constant Typically 15.0 seconds in still air

Typically 0.4 seconds in stirred oil

Maximum power rating 10 mW at 25°C to 1mW at 100°C

ORDERING MAPS

L S M N 4 0 0 A


Resistance at25°C

2252 = 2,252 Ohms

Overall Length orSpecial Options

Wire Gauge and Probe Diameter

2 = #28AWG, 0.055” Probe Diameter3 = #32AWG, 0.035” Probe Diameter

L S M N 7 0 0

R-T CurveA = A CurveB = B Curve

Resistance at25°C

006K = 6,000 Ohms010K = 10,000 Ohms030K = 30,000 Ohms


Wire Gauge and Probe Maximum Diameter

2 = #28AWG, 0.055” Probe Diameter3 = #32AWG, 0.035” Probe Diameter


Tolerancesat 25°C1 = ±1%2 = ±2%3 = ±3%5 = ±5%


70°CA = ±1.0°CB = ± 0.5°CC = ±0.2°CD = ±0.1°C

Tolerancesat 25°C1 = ±1%2 = ±2%3 = ±3%5 = ±5%


70°CA = ±1.0°CB = ± 0.5°CC = ±0.2°CD = ±0.1°C Note: Other accuracy

temperature ranges areavailable upon request.

Micro NTC Thermistor ProbesLSMC Series 0.0185” (0.469) and 0.0190” (0.0480) probe diameters



.0185” (.469) Max.

.156” (3.96)Nominal AWG 38 Heavy Isomid insulation


These tiny thermistors can be used in many Life Science applications. Theyare small enough to fit into a hypodermic needle. These quick responseLSMC Series thermistors can be used to monitor temperature in manyindustry applications.

LSMC 700 Series10K Ohms, 30K Ohms, or 100K Ohms at 25°C “A” Curve

.0190” (.48) Max.

.30” (7.62) Nominal AWG 38 Heavy Isomid insulation


LSMC 400 Series2252 Ohms at 25°C “A” Curve

Other base resistances may be available - Contact Selco. Detailed R-T tableinformation can be found on pages 24-25.

SPECIFICATIONS

Temperature rating/ LSMC Series thermistors may be recommended operating intermittently cycled at temperaturesranges from -50°C to 150°C. Optimum stability

is achieved when these thermistors areoperated continuously at or below 125°C.

Curves/Betas (25/85) A curve (3977K) or B curve (3942K) Detailed curve material information on pages 24-25.

Accuracies ±0.1°C, ±0.2°C, ±0.5°C, ±1.0°CAccuracy Temp Range 0°C to 70°CTolerances at 25°C ±1%, ±2% , ±3%, ±5%

Dissipation constant 0.3 mW/°C in still air2.5 mW/°C in stirred oil

Thermal time constant Typically 5.0 seconds in still airTypically 0.4 seconds in stirred oil

Maximum power rating 10 mW at 25°C to 1 mW at 100°C

ORDERING MAP

L S M C 4 0 0 A


Resistance at25°C

2252 = 2,252 Ohms


L S M C 7 0 0 A


Resistance at25°C

010K = 10,000 Ohms030K = 30,000 Ohms100K = 100,000 Ohms



FEATURESl Interchangeable accuraciesl Quick responsel Moisture coating optional l RoHS Compliant

Tolerancesat 25°C1 = ±1%2 = ±2%3 = ±3%5 = ±5%


70°CA = ±1.0°CB = ± 0.5°CC = ±0.2°CD = ±0.1°C

Tolerancesat 25°C1 = ±1%2 = ±2%3 = ±3%5 = ±5%


70°CA = ±1.0°CB = ± 0.5°CC = ±0.2°CD = ±0.1°C

Note: Other accuracytemperature ranges areavailable upon request.

Interchangeable NTC ThermistorsIN Series



SPECIFICATIONS

Temperature rating/ IN Series thermistors may berecommended operating intermittently cycled at temperaturesranges from -50°C to 150°C. Optimum stability

is achieved when they are operated or below 125°C

Resistance at 25°C See IN Series ordering map on page 14

Curves/Betas (25/85) A Curve = 3977KB Curve = 3942KC Curve = 3695KD Curve = 4262KF Curve = 3435KK Curve = 3485KOthers available upon request

Accuracies ±0.05°C±0.10°C±0.20°C±0.50°C±1.00°C

Accuracy temperature -20°C to 50°C 20°C to 90°Cranges 0°C to 50°C -40°C to 40°C

20°C to 45°C 50°C to 125°C0°C to 70°C -20 to 125°C0°C to 100°C



Maximum power rating 30 mW at 25°C to 1 mW at 100°C

Note: The 10K Ohm base resistance, with a 3977K (25/85) Beta (A Curve),is UL 1434 certified.

FEATURESl Precision interchangeability l Accuracies as high as ±0.05°C to ±0.10°C l Quick thermal responsel Excellent field stabilityl RoHS Compliant

Selco’s IN Series NTC thermistors are interchangeable andhave a variety of accuracy temperature range options. TheseIN Series thermistors can be PCB mounted or packaged inprotective housings to meet application requirements

Interchangeable NTC ThermistorsIN Series - Order Map



IN- - - XX

R-T CurveA = Curve A D = Curve DB = Curve B F = Curve FC = Curve C K = Curve KX = New letter assigned for special curve

Resistance at 25°C001K = 1K Ohms003K = 3K Ohms006K = 6K Ohms010K = 10K Ohms020K = 20K Ohms030K = 30K Ohms100K = 100K Ohms2252 = 2,252 OhmsX = special base resistance value

Interchangeable AccuraciesA = ±1.0°C D = ±0.1°CB = ±0.5°C E = ±0.05°CC = ±0.2°C X = Special

Accuracy Temperature Ranges1 = +20°C to 45°C 6 = -40°C to 40°C2 = -20°C to 50°C 7 = +50°C to 125°C3 = 0°C to 70°C 8 = 0°C to 50°C4 = 0°C to 100°C 9 = -20°C to 125°5 = +20°C to 90°C X = new digit assigned for specials

2” Overall LengthCode AWG Lead O.D. Lead Type Chip Coating Code AWG Lead O.D. Lead Type Chip Coating

05060708091011121314161820

26283230262632323030283228

0.0169”0.0126”0.008”0.010”

0.0159”0.0159”0.008”0.008”0.010”0.010”

0.0126”0.008”

0.0126”

Tinned CopperTinned CopperTinned Copper

NickelTinned Alloy 180Tinned Copper

NickelTinned Copper

Tinned Alloy 180Tinned Copper

Tinned Alloy 180Tinned Alloy 180

Nickel

EpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxy

2122242628303141*

3232302832303030

0.008”0.008”0.010”

0.0126”0.008”0.010”0.010”0.010”

NickelTinned CopperTinned CopperTinned Copper


TeflonAg/Cu Twisted Kynar

EpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxy

3” Overall Length

* 6K to 30K only

For optional overall lengths other than 2” or 3” substitute XX withlengths in inchesExample: 04 = 4.0”

The ±0.05°C accuracy, over 0°C to 50°C, may be available with a number of base resistances and Betas. Please contact Selco foravailability.

The IN Series 10K Ohm base resistance, with a 3977K Beta, hasUL 1434 Certification. Contact Selco for assistance

Contact Selco for other base resistances, Betas, or accuracies/accuracy temperature ranges.

ORDERING MAP

DO-35 Glass Encapsulated NTC ThermistorsDT Series



FEATURESl Glass sealed body for high reliability l High stability and low costl Excellent thermal cycle endurance l Leads may be cut or formedl Optional interchangeable accuracy l 250C or 300C thermal ratingl Some DTs with UL1434 Certification l RoHS Compliant

The DT thermistor is a DO-35 NTC thermistor and is available with a tolerance at 25°C or with an interchangeable accuracy of±0.2°C over 0° to 70°C. This is highly stable thermistor can be PCB mounted or packaged in a protective housing to meet yourapplication requirements.

SPECIFICATIONS

Temperature range -50°C to 250°CContinuous operating temp range -50°C to 200°COptional temperature range -50°C to 300°CContinuous operating temp range -50°C to 260°CResistance at 25°C 10,000 Ohms

15,000 Ohms30,000 Ohms47,000 Ohms50,000 Ohms100,000 Ohms200,000 Ohms500,000 Ohms

Curves/Betas (25/85) A Curve = 3977KB Curve = 3942KD Curve = 4262KF Curve = 3425KOther Curves/Betas available upon request

Accuracy ±0.2°C over 0°C to 70°CTolerances at 25°C ±1%, ±3%, ±5%Dissipation constant 2.0 mW/°C in still air


Typically 1.0 seconds in stirred oilMaximum power rating 250 mW at 25°C to 100 mW at 100°C

ORDERING MAP

DT - -

R-T CurveA = Curve AC = Curve CD = Curve DF = Curve FX = Special

Resistance at 25°C010K = 10K Ohms015K = 15K Ohms030K = 30K Ohms047K = 47K Ohms050K = 50K Ohms100K = 100K Ohms200K = 200K Ohms500K = 500K OhmsX = Special base resistance value

Optional SpecialSpecification

Note: Some of the DT Series part numbers may have UL 1434 certification. Please contact Selco Products or visit our website for availability.


Tolerancesat 25°C1 = ±1%3 = ±3%5 = ±5%

Accuracies C = ±0.2°C Accuracy

TemperatureRange

3 = 0°C to 70°CTolerance

0 = *

Optional 300°CRating

H = 300°C rating

*Use 0 when the DT series is tolerance based andhas a 300°C maximum temperature rating.

Radial Glass Bead ThermistorsRG Series



FEATURESl Glass sealed radial lead thermistorsl Quick response timel Excellent stability and moisture resistancel RoHS Compliant

These tiny radial glass bead thermistors are moisture resistant.They can be PCB mounted or easily packaged into small diameter custom probe assemblies.

SPECIFICATIONS

Temperature range -50°C to 300°CContinuous operating temp range -50°C to 260°C

Resistance at 25°C 10,000 Ohms50,000 Ohms100,000 Ohms

Curves/Betas (25/85) A Curve = 3977KF Curve = 3435K

Tolerances at 25°C ±1%, ±2%, ±3%, ±5%




ORDERING MAP

R G - -

R-T CurveA = Curve AF = Curve FX = New letter assigned forspecial curve

Resistance at 25°C010K = 10K Ohms050K = 50K Ohms100K = 100K Ohms

Tolerance at25°C

1 = ±1% 2 = ±2%3 = ±3%5 = ±5%

Note: Other thermistor base resistances, Betas, or tolerances may be available. Please contact Selco Products.


Glass BeadDiameterA = 0.063”

Note: Other glass bead diameters may be available upon request

Point Matched NTC ThermistorsPM Series



FEATURESl Tolerance resistance matched to specific temperaturel Excellent field stabilityl Cost effective discrete thermistorl RoHS Compliant

PM Series thermistors are precision tested at a chosentolerance for a specific temperature. This cost effectivethermistor provides an advantage to industries with highvolume applications, such as in HVAC, automotive, andindustrial markets.

SPECIFICATIONS

Temperature rating/ PM Series thermistors may berecommended operating intermittently cycled at temperaturesranges from -50°C to 150°C. Optimum stability

is achieved when they operated ator below 125°C

Curves/Betas (25/85) A Curve = 3977KB Curve = 3942KC Curve = 3695KD Curve = 4262KF Curve = 3435K

Tolerances at ±1.0°Ctemperature points ±1%

±2%±3%±5% ±10%

Temperature points -20°C0°C25°C37°C70°C100°C

Other temperature points available upon request



Maximum power rating 30 mW at 25°C to 1mW at 100°C

Point Matched NTC ThermistorsPM Series - Order Map



PM - - - XX

R-T CurveA = Curve A D = Curve DB = Curve B F = Curve FC = Curve C X = New letter assigned for special curve

Resistance at 25°C001K = 1K Ohms005K = 5K Ohms006K = 6K Ohms010K = 10K Ohms100K = 100K Ohms2252 = 2,252 Ohms1MEG = 1 Million OhmsX = Special base resistance value

Tolerance at Temperature Point1 = ±1% 0 = ±10%2 = ±2% A = 1.0°C3 = ±3% X = Special5 = ±5%

Temperature PointsA = -20°C E = 70°CB = 0°C F = 100°CC = 25°C X = SpecialsD = 37°C

2” Overall LengthCode AWG Lead O.D. Lead Type Chip Coating Code AWG Lead O.D. Lead Type Chip Coating

05060708091011121314161820

26283230262632323030283228

0.0169”0.0126”0.008”0.010”

0.0159”0.0159”0.008”0.008”0.010”0.010”

0.0126”0.008”

0.0126”

Tinned CopperTinned CopperTinned Copper

NickelTinned Alloy 180Tinned Copper

NickelTinned Copper

Tinned Alloy 180Tinned Copper

Tinned Alloy 180Tinned Alloy

Nickel

EpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxy

2122242628303141*

3232302832303030

0.008”0.008”0.010”

0.0126”0.008”0.010”0.010”0.010”

NickelTinned CopperTinned CopperTinned Copper


TeflonAg/Cu Twisted Kynar

EpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxy

3” Overall Length

* 6K to 30K only

For optional overall lengths other than 2” or 3” substitute XXwith lengths in inchesExample: 04 = 4.0”

ORDERING MAP


Thin Fi lm NTC ThermistorsTF Series



FEATURESl UL 1434 certifiedl Thin film insulatedl Leads can be attachedl RoHS compliant

The TF Series thin film thermistor is able to monitor temperature in small spaces and is perfect for battery pack or charger applications.

SPECIFICATIONS

Temperature range -50°C to 90°CContinuous operating temp range -50°C to 76°COptional temperature range -50°C to 125°CContinuous operating temp range -50°C to 105°C

Resistance at 25°C 10,000 Ohms

Curves/Betas (25/85) A Curve=3977KF Curve=3435K

Tolerances at 25°C ±1%±3%±5%



Maximum power rating 3.5 mW at 25°C to 1.1 mW at 100°C

ORDERING MAP

T F - - 0 1 0 K - -

Tolerances1 = ±1%3 = ±3%5 = ±5%

Overall Length1 = .59” (15mm)2 = .98” (25mm)3 = 1.97” (50mm)4 = 2.95” (75mm)

Note:L: .59” (15mm)

.98” (25mm)1.97” (50mm)2.95” (75mm)

R-T CurveA = A CurveF = Curve FX = Special

Resistance at 25°C010K = 10K OhmsX = Special base resistance value

Note: TF Series thermistors are UL certified.Note: 125°C temperature rating is identified by optional special specification



Insulated Lead Epoxy ThermistorsTS Series



Polyurethane Insulation.063” (1.6) Max.

.118”± .039” (3.0 ± 1.0)

3.42”± .118” (87.0 ± 3.0)

Epoxy Coating (Black)

Copper Alloy Insulated wire - 32AWG

.157” (4.0) Max.

FEATURESl Quick response timel Bead diameter of 0.063”l Polyurethane insulated leadsl RoHS Compliant

The TS Series thermistor features a very small bead, insulatedleads, and quick thermal time constant.

SPECIFICATIONS

Temperature range -50°C to 110°CContinuous operating temp range -50°C to 92°CResistance at 25°C 1,000 Ohms

2,000 Ohms2,252 Ohms4,000 Ohms5,000 Ohms

10,000 Ohms20,000 Ohms30,000 Ohms50,000 Ohms

100,000 Ohms232,000 Ohms

Curves/Betas (25/85) A = Curve AB = Curve BC = Curve CD = Curve DF = Curve FX = New letter assigned for special curve

Tolerances at 25°C ±1%, ±3%, ±5%Dissipation constant 0.3 mW/°C in still air


Typically 0.8 seconds in stirred oilMaximum power rating 3.5 mW at 25°C to 1.25 mW at 100°C

ORDERING MAP

T S - -

R-T CurveA = Curve AB = Curve BC = Curve CD = Curve DF = Curve FX = New letter assigned forspecial curve

Resistance at 25°C001K = 1K Ohms002K = 2K Ohms2252 = 2252 Ohms004K = 4K Ohms005K = 5K Ohms010K = 10K Ohms020K = 20K Ohms030K = 30K Ohms050K = 50K Ohms100K = 100K Ohms232K = 232K OhmsX = Special base resistance value

Tolerance at25°C

1 = ±1%3 = ±3%5 = ±5%



Short Lead NTC Epoxy ThermistorsHP Series



.14” (3.5) Max.

.16” (4.0) Max.

.03” (0.7)Tiebar cut

0.10 0.25(2.54 0.25)

±±

0.67”±.06(17±1.5)

0.34” ±1(8.5±1)

0.12” (3.0) Max.

Blue colorEpoxy resin

.02” ( 0.5)Tin-PlatedCopper

.02” ( 0.5)Tin-PlatedCopper Leads

FEATURESl High stability and low costl Tiebar cut allows consistent PCB placementl RoHS Compliant

The HP thermistor is a low cost, tolerance basedthermistor.

SPECIFICATIONS


2,000 Ohms5,000 Ohms10,000 Ohms20,000 Ohms47,000 Ohms100,000 Ohms


Tolerances at 25°C ±1%, ±3%, ±5%Dissipation constant 0.5 mW/°C in still air


Typically 0.9 seconds in stirred oilMaximum power rating 10 mW at 25°C to 0.25 mW at 100°C

ORDERING MAP

H P - - -

R-T CurveA = Curve AB = Curve BC = Curve CD = Curve DF = Curve FX = New letter assigned for special curve

Resistance at 25°C001K = 1K Ohms002K = 2K Ohms005K = 5K Ohms010K = 10K Ohms020K = 20K Ohms047K = 47K Ohms100K = 100K OhmsX = Special base resistance value

Tolerances1 = ±1%3 = ±3%5 = ±5%



Long Lead NTC Epoxy ThermistorsHT Series



.157” (4.0) Max.

.157” (4.0) Max.

1.18”±.059”(30±1.5)

0.1” (2.54)

.019” ( 5)Tin-PlatedCopper Leads

.019” ( 5)Tin-PlatedCoppper Leads

.138” (3.5) Max.

Black colorEpoxy resin

FEATURESl High stability/low costl Long leads for PCB positioningl RoHS compliant

The HT thermistor is a low-cost, tolerance based thermistor with longer leads than the HP Series.

SPECIFICATIONS


2,000 Ohms5,000 Ohms10,000 Ohms20,000 Ohms47,000 Ohms100,000 Ohms


Tolerances at 25°C ±1%, ±3%, ±5%




ORDERING MAP

H T - - -

R-T CurveA = Curve AB = Curve BC = Curve CD = Curve DF = Curve FX = New letter assigned for special curve

Resistance at 25°C001K = 1K Ohms002K = 2K Ohms005K = 5K Ohms010K = 10K Ohms020K = 20K Ohms047K = 47K Ohms100K = 100K OhmsX = Special

Tolerances1 = ±1%3 = ±3%5 = ±5%



Technical NotesNegat ive Temperature Coeff ic ient (NTC) Thermistors



Thermistor DefinitionThe word thermistor is derived from its description “thermal sensitiveresistor” Thermistors are passive semiconductors, which produceresistance values dependent on temperature.A Negative Temperature Coefficient (NTC) thermistor decreasesin resistance as its body temperature increases. In fact, NTCthermistors exhibit two characteristics, which make them extremelyuseful in a variety of applications. Their change in resistance ispredictable and it is relatively large per degree change in temperature.

Manufacturing ProcessThis is a two-step process of chip manufacturing and thermistorassembly. Manufactured chips are processed by metal oxide powdersinto ceramic sheets. These sheets are metalized with silver to allowfor electrical contact. After metalization, the ceramic sheets arediced into chips. Each chip is tested to meet our superior qualitystandards.After a chip has been manufactured and tested, leads are attached.The chip is trimmed to meet the specified tolerance, and then aprotective coating is added. Further customizing of the assemblycan be done by adding housings, cables, and connectors.Thermistor quality is assured with in-process inspection andStatistical Process Control (SPC). This process takes place at eachmanufacturing and assembly step. All finished products are 100%tested both electrically and mechanically to guarantee all specificationsare met.

Resistance-Temperature (R/T) Curves and Negative Temperature CoefficientNine different materials are made, each with its own unique andpredictable resistance-temperature characteristics. These characteristicsare called ‘curves’. Thermistors are most often specified by theircurve and by their resistance value at 25°C.The NTC (Negative Temperature Coefficient) is the negative percentresistance change per degree C. Our thermistors have NTC valuesat 25°C ranging from -3.7%/°C to -6.4%/°C. Resistance values at25°C range from 300 ohms to 1 meg ohms. The tables on pages26-27 detail this information.

Thermal Time ConstantTime constant, expressed in seconds, is the time required for athermistor to indicate 63.2% of a newly impressed temperature. Thetime constant of a thermistor is directly affected by the mass of thethermistor and thermal coupling to the environment. An epoxy orphenolic coated thermistor with a 0.095” O.D., will typically have atime constant of 0.75 seconds in stirred oil and 10 seconds in stillair.

Dissipation ConstantDissipation constant is the power required to raise the temperatureof a thermistor 1°C above the surrounding environment. Power isexpressed in watts. The dissipation constant of a thermistor with a0.095” O.D., coated with epoxy or phenolic, is typically 13 mW/°C instirred oil and 2 mW/°C in still air.

Voltage/Current RequirementsVery low current is required for a thermistor being used in temperaturemeasurement, control or compensation applications. Current levelsshould typically be less than 100mA for a thermistor to dissipate“zero power”. As previously discussed, power dissipation for athermistor in still air is approximately 2mW/°C. Therefore, in orderto keep the thermal error (self-heat) below 0.1°C, the powerdissipation must be less than 0.2 mW.

Self-heating is desirable in applications such as air flow measurementand liquid level control. Standard epoxy or phenolic coated thermistorswith a 0.095” O.D., have a maximum power rating of 30 milliwatts at25°C to 1 milliwatt at 100°C.

Beta

The Beta value describes the steepness of R/T curve. The largervalue Beta equals a steeper R/T curve. The Beta value of a thermistoris one way to characterize its resistance temperature relationship.Beta is dependent on two reference temperatures. Selco Productsuses 25°C and 85°C as its standard. Beta is calculated as follows:

$ T2/T1 = Ln(RT2/RT1)/(1T2 - 1T/1)

Temperature is in degrees Kelvin; RT1 is the resistance attemperature T1; RT2 is the resistance at temperature T2.

Steinhart-Hart Equation

The Steinhart-Hart Equation is an empirically developed polynomialwhich best represents the resistance-temperature relationships ofNTC thermistors. The Steinhart-Hart Equation is more accuratethan previous methods. Specifically, it is more accurate over widertemperature ranges. To solve temperature when resistance isknown, the form of the equation is:

1/T=a+b(Ln(R))+c(Ln(R))3

To solve for resistance when temperature is known, the form of theequation is:

R=e(exp)[-a/2+(a2/4+a3/27)-2)-3+(-a/2-(a2/4+a3/27)2)3]

where alpha = (a-1/T)/c and $ = b/c

For both forms of the equation T is temperature expressed indegrees Kelvin; a, b, and c can be solved simultaneously using thefollowing:

1/T1=a+b(LnR1)+c(LnR1)3



The data calculated by these equations will be accurate to betterthan ±0.01°C when -40°C is less than or equal to 150°C and |T1-T2|is less than or equal to 50°C and |T2-T3| is less than or equal to50°C and T1, T2, and T3 are evenly spaced.

Maximum Temperature Rating/Recommended Operating Ranges

Our thermistors may be intermittently cycled at temperatures from-50°C to 150°C. Stability is achieved when the thermistors arestored at temperatures less than 50°C and operated continuously attemperatures less than 100°C. The DT Series thermistor has atemperature range from -50°C to +250°C. For interchangeablethermistors, optimum stability is achieved when the thermistors areoperated at temperatures within the specified temperature range.

Stability

Years of experience in thermistor manufacturing, coupled withstringent process controls, ensures that highly stable thermistors areproduced. In fact, our thermistors typically exhibit less than 0.02°Cthermometric drift per year when stored or operated at temperaturesless than 50°C. The stability of a thermistor is greatly dependent onenvironmental conditions such as humidity, excessive temperaturesand thermal shock. These effects should be minimized to guaranteestability.

Resistance - Temperature Table



Ratio is the resistance at temperature divided by the resistance at 25°C. To find the actual resistance value at the temperatures listed in thecharts, multiply the R25 value by the number listed in the Ratio column next to the corresponding temperature.

As an example, a Curve A thermistor with a temperature tolerance of ±1°C over the temperature range 0° to 70°C would have the followingresistance tolerance: 0°C = ±5.1%; 25°C = ±4.4%; 70°C = ±3.4%

NTC (Negative Temperature Coefficient) is the negative percent resistance change per degree C. To determine the resistance tolerance of aprecision thermistor at any temperature point multiply the temperature tolerance times the NTC.

Typical R25 = 1K to 100K

RT/R25 RATIO

RATIO NTC

Curve A


RT/R25 RATIO

RATIO NTC

Curve B


RT/R25 RATIO

RATIO NTC

Curve C


RT/R25 RATIO

RATIO NTC

Curve D


RT/R25 RATIO

RATIO NTC

Curve E

Temperature °C

-50-45-40-35-30-25-20-15-10-505

10152025303537404550556065707580859095100105110115120125130135140145150

67.1347.2633.6924.2917.7113.059.7117.2975.5344.2343.2662.5401.9911.5721.2491.000

0.80560.65300.60140.53250.43670.36010.29850.24870.20820.17520.14800.12560.1071

0.091610.078700.067860.058730.051000.044440.038850.034080.029970.026450.023400.020760.01487

7.16.96.76.46.26.05.85.65.45.35.15.04.84.74.54.44.34.14.14.03.93.83.73.63.53.43.33.23.23.13.02.92.92.82.72.72.62.52.52.42.42.3

56.3940.5629.4821.6416.0311.999.0406.8755.2704.0713.1682.4831.9591.5561.2441.000

0.80880.65790.60660.53800.44230.36540.30340.25310.21210.17850.15080.12800.1091

0.093270.080060.068970.059620.051710.045000.039280.034390.030200.026600.023490.020800.01846

6.76.56.36.15.95.75.65.45.25.14.94.84.74.54.44.34.24.14.04.03.93.83.73.63.53.43.33.23.23.13.02.92.92.82.82.72.62.62.52.52.42.4

44.1332.3623.9717.9213.5210.297.8916.1024.7543.7312.9492.3461.8791.5141.2271.000

0.81960.67540.62600.55940.46550.38930.32700.27600.23380.19900.17000.14570.12540.1084

0.093920.081680.071270.062370.054760.048210.042570.037690.033460.029790.026580.02377

6.36.15.95.35.65.45.25.14.94.84.64.54.44.34.14.03.93.83.83.73.63.53.43.43.33.23.13.03.02.92.82.82.72.62.62.52.52.42.42.32.32.2

82.3657.3040.3428.7220.6715.0211.038.1746.1134.6113.5072.6892.0771.6171.2671.000

0.79430.63490.58150.51060.41300.33590.27470.22590.18660.15490.12930.10830.091150.077040.065380.055700.047640.040890.035220.030450.026410.022980.020060.017560.015420.01358

7.47.16.96.76.56.36.15.95.75.65.45.25.14.94.84.74.54.44.44.34.24.14.03.93.83.73.63.53.43.33.23.23.13.02.92.92.82.82.72.62.62.5

89.6962.2543.6930.9822.2016.0611.738.6446.4254.8163.6382.7702.1251.6421.2771.000

0.78810.62500.57060.49860.40010.32280.26190.21360.17500.14410.1193

0.099150.082780.069410.058440.049400.041920.035710.030530.026190.022540.019470.016870.014670.012790.01118

7.47.27.06.86.66.46.26.05.85.75.55.45.25.15.04.84.74.64.54.54.34.24.14.03.93.83.73.73.63.53.43.33.23.23.13.03.02.92.82.82.72.7

$ at 0°C/50°C 3892K 3813K 3575K 4141K 4276K

4262K 4434K3695K3942K3977K$ at 25°C/85°C

3320K

Resistance - Temperature Table



3435K

Typical R25 = 10K

RT/R25 RATIO

$ at 25°C/85°C

RATIO NTC

Curve F

4390K

Typical R25 = 10K

RT/R25 RATIO

RATIO NTC

Curve G

4847K

Typical R25 = 1MEG

RT/R25 RATIO

RATIO NTC

Curve H

3485K

Typical R25 = 200 to 2K

RT/R25 RATIO

RATIO NTC

Curve I Curve K

4144K

Typical R25 = 100K

RT/R25 RATIO

RATIO NTC

Curve P

Temperature °C

-50-45-40-35-30-25-20-15-10-505

10152025303537404550556065707580859095

100105110115120125130135140145150

32.9524.7718.8514.4111.138.6436.7775.3414.2473.39

2.7282.2051.7961.4691.2091.000

0.83130.694

0.58270.49120.41610.35360.302

0.25880.22280.19240.16680.14510.12660.1108

0.097310.085720.07576

6.26.05.85.65.45.25.04.84.74.54.44.24.14.03.93.73.63.5

3.43.33.23.13.13.02.92.82.72.72.63.02.52.42.4

95.8465.6645.7232.0622.8216.3711.918.7276.4724.8343.65

2.7722.1251.64

1.2771.000

0.78880.6259

0.50030.402

0.32510.26420.21610.17750.14660.12150.1013

0.084830.071350.060250.051110.043510.03720.0319

0.027460.02371

8.17.87.57.27.06.76.56.36.05.85.75.55.35.15.04.84.74.5

4.44.34.14.03.93.83.73.63.53.43.33.33.23.13.02.92.92.8

14.6510.517.6075.5564.0933.0412.2771.7181.3061.000

0.77100.59840.54170.46750.36750.29070.23120.15800.14880.1204

0.097840.079930.065610.054110.044830.037300.031170.026150.022030.018630.015810.013470.011520.009880.008500.00734

6.16.66.46.26.05.95.75.65.45.35.15.05.04.94.84.64.54.44.34.24.14.03.93.83.73.63.63.53.43.33.23.23.13.03.02.9

39.1828.8821.5016.1812.289.4157.2785.6734.4573.5282.8132.2591.8261.4851.2151.000

0.82770.68870.64080.57600.48420.40890.34690.29560.25300.21740.18750.16230.14110.12300.1076

0.094500.083220.073510.065120.057860.05154

6.26.05.85.65.45.25.14.94.74.64.54.34.24.14.03.83.73.63.63.53.43.33.23.23.13.02.92.82.82.72.62.62.52.52.42.32.3

33.5824.4117.9113.269.8987.4525.6554.3253.3312.5852.0191.5871.2561.000

0.80080.64500.59240.52240.42530.34800.28620.23650.19640.16380.13720.1154

0.097420.082600.070300.060050.051480.044290.038230.033100.028760.025060.021900.019200.0168

0.01487

6.56.36.35.95.85.65.45.35.15.04.94.74.64.54.44.34.24.24.14.03.93.83.43.63.53.43.33.33.23.13.03.02.92.82.82.72.72.62.62.5

$ at 0°C/50°C 4269K 4669K 3405K 3988K

3535K

3419K


RT/R25 RATIO

RATIO NTC

20.6815.6711.9989.2417.1895.6234.4393.5182.8122.2581.8281.4861.16

1.0000.82670.68650.63840.57350.48090.40540.34300.29160.24880.21330.18340.1584

0.137240.119290.104020.091020.079900.070380.062160.055050.048880.043510.038830.034720.031120.02796

6.05.75.55.35.25.04.84.74.54.44.24.14.03.93.73.63.63.53.43.33.23.23.13.02.92.82.82.72.62.62.52.42.42.32.32.22.22.12.12.0

Appl icat ion Notes



NTC Thermistor ApplicationsIntroduction

Our NTC chip thermistors are excellent solutions in applicationsrequiring temperature measurement and compensation from -50°to 150°C.

RTDs, thermocouples and silicon semiconductors cannot competewith the thermistor’s sensitive response to temperature. Thissensitivity is crucial for accurate temperature measurement.

Unlike RTDs and thermocouples, thermistors are virtuallyunaffected by lead resistance. This makes NTC thermistors thesensor of choice for remote sensing applications. With theirexcellent long term stability characteristics, design engineers utilizethermistors in critical applications for the medical, military,aerospace, industrial and scientific industries.

Systems utilizing thermistors are less expensive to produce thanother solutions because fewer associated components are requiredfor a high performance system. Chip thermistors can be orderedwith tight tolerances to ±0.1°C, eliminating the costly calibrationprocess required by temperature sensors such as siliconsemiconductors, RTDs, thermocouples and glass beaded and diskthermistors with loose tolerances.

NTC thermistors provide the design engineer with desirable sensorperformance advantages in a variety of applications. The followingnotes provide a few examples of how to utilize the NTC thermistor.

“Zero Power” Sensing - Dissipation Constant

When utilizing a thermistor for temperature measurement, control,and compensation applications, it is very important not to “self-heat”the thermistor. Power, in the form of heat, is produced when currentis passed through the thermistor. Since a thermistor’s resistancechanges when temperature changes, this “self generated heat” willchange the resistance of the thermistor, producing an erroneousreading.

The power dissipation constant is the amount of power requiredto raise a thermistor’s body temperature 1°C. A standard chipthermistor has a power dissipation constant of approximately2mW/°C in still air. In order to keep the “self-heat” error below 0.1°Cpower dissipation must be below 0.2mW. Very low current levels arerequired to obtain such a lower power dissipation factor. This modeof operation is called “zero power” sensing.

Thermistor Linearization - Voltage ModeWheatstone Bridge - Voltage Mode

To produce a voltage output that varies linearly with temperature,utilize the NTC thermistor as the active leg in a Wheatstone Bridge.As temperature increases, the voltage output increases. The circuitin Figure 1 produces an output voltage that is linear with ±0.06°Cfrom 25°C to 45°C. This circuit is designed to produce 1V at 25°Cand 200mW at 45°C; this is achieved by the selection of R2 and R3.The value of R1 is selected to best provide linearization of the 10Kohm thermistor over the 25°C to 45°C temperature range. Figure 2illustrates the output voltage of the Wheatstone Bridge as a functionof temperature.

The circuit in Figure 3 provides improved output accuracy over awide temperature range by substituting a 6K/30K ohm thermistornetwork in place of the single thermistor in the Wheatstone Bridge.This circuit is designed to provide 0V at 0°C and 537mV at 100°C.The maximum linear deviation of this circuit is ±0.234°C from 0°C to100°C.

Figure 1: Wheatstone Bridge - Voltage ModeT1 = 10K ohm “A” CurveR1 = 4980 ohmR2 = 4980 ohmR3 = 10K ohm

Figure 2: Wheatstone Bridge - Voltage Mode

Figure 3: Wheatstone Bridge - Voltage ModeT1 = 30K ohm “B” CurveT2 = 6K ohm “A” CurveR1 = 5420 ohmR2 = 3970 ohmR3 = 3970 ohmR4 = 24720 ohm

Appl icat ion Notes



Thermistor LinearizationOperational Amplifier - Resistance Mode

A linear voltage output that varies with temperature can also beproduced by utilizing an operational amplifier and a linearizedthermistor network as illustrated in Figure 4. The voltage outputdecreases linearly as temperature increases. This circuit may becalibrated by adjusting R3 for an output voltage of 200mW at 25°Cand 0V at 45°C.

Temperature Measurement and ControlDigital Thermometer

The most common application for the NTC thermistor is temperaturemeasurement. Accurate temperature measurement can easily beaccomplished by interfacing a Wheatstone Bridge, 6K/30K ohmthermistor network and a digital voltmeter integrated circuit asillustrated in Figure 5. The IC consist of an analog to digitalconverter with built-in 3-1/2 digit LCD driver providing resolution of0.1°C. Using the 6K/30K ohm thermistor network makes it possibleto achieve an overall system accuracy of ±0.4°C from 0°C to 100°C.This digital thermometer can easily be interfaced with additionalcircuitry to provide a temperature control circuit with a digital display.

Micro Controller System

The advent of low cost micro controllers used with precisioninterchangeable NTC thermistors, provides the design engineer withunlimited design possibilities for temperature measurement andcontrol systems. These systems are relatively inexpensive toproduce yet offer very high temperature accuracy and varioussoftware controlled outputs.

For example, a micro controller system utilizing remote thermistorsensors can monitor and control the temperature in severallocations in an office building. For this case, the micro controller iscomprised of a built-in microprocessor, analog to digital converter,RAM and several digital inputs/outputs. The complete systemFigure 6 utilizes the micro controller, multiplexer, EPROM, digitaldisplay, keypad and display driver.

The micro controller is programmed in assembler language. Thetemperature measurement is calculated within the micro controllerusing the resistance versus temperature algorithm and the a, band c, constants for the specific thermistor resistance and curvematerial. Refer to the Steinhart Equation on page 5. An alternativemethod to convert the thermistor resistance to temperature is toprogram a “look-up” table in EPROM. After programming, the microcontroller tells the multiplexer to send back temperature data froma particular zone (room in the office building) and converts theresistance of the thermistor into a temperature reading.

The micro controller can then turn on or off the heating or airconditioning systems in a specific zone.

The thermistor/micro controller system can be used for security,temperature control, monitoring activities and many otherapplications. The possibilities are endless.

Figure 4: Linearization - Resistance ModeT1 = 10K ohm “A” CurveR1 = 4980 ohmR2 = 5K ohmR3 = 10K ohm potentiometer

Figure 5: Digital ThermometerR7 = 1.50K ohmR8 = 100K ohmR9 = 470K ohmR10 = 15K ohmC1 = 100 pFC2 = 0.22C4 = 0.1

Figure 6: Micro Controller System

Appl icat ion Notes



Temperature Compensation

NTC thermistors can be used to compensate for the temperaturecoefficient response of various components such as crystaloscillators, mechanical meters and infrared LEDs. A thermistor/resistor network Figure 7 is placed in series with a PTC componentrequiring compensation. The resistor values are selected to providethe proper NTC slope to offset the PTC component. The net effectis a constant circuit response that is independent of temperature.

“Self-Heat” Sensing Applications

To “self-heat” a thermistor, it must be subjected to power levels thatraise the thermistor’s body temperature above the environmentalsurroundings. Self-heat applications include the sensing of liquid,air level, and flow rates. This application is dependent on the factthat the environment surrounding a thermistor directly affects theamount of power the thermistor can dissipate. For example,submerged in liquid, a thermistor can typically dissipate 500% to600% more power than it can air.

Therefore, a thermistor being “self-heated” in air is able to dissipatemuch more power when transferred to a fluid environment. Thisincrease in power dissipation generates a significant increase inresistance. It is this change in resistance, which makes it possibleto sense the fluid level.

A simple liquid level control system can be designed by putting athermistor in series with a coil Figure 8, which operates a valve thatreleases the liquid in the tank. The thermistor is placed in the tankand operated in a “self-heat” mode.

In air, the thermistor’s resistance is low and allows enough currentflow to energize the relay coil and keep the relay contact closed.When the fluid level in the tank surrounds the thermistor, itsresistance increases and de-energizes the relay, which opens avalve and releases the fluid. As the fluid is released from the tank,the thermistor’s resistance decreases and the relay coil energizesand closes the valve.

Fuel injection in automobiles utilize the thermistor in the “self-heat”mode in order to properly control the air/fuel mixture. Forced airheaters may use the NTC thermistor in the “self-heat” mode in orderto maintain proper air flow characteristics. This technology isutilized to monitor the flow rate and level of air and fluids in avariety of applications.

Figure 7: Temperature Compensation

Figure 8: Self-Heat Applications

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