Contact Temperature sensor Calibration

Contents• What is Calibration• When Calibration is required• Method of Calibration

• Primary Calibration• Fixed Point calibration• Maintenance Apparatus

• Secondary Calibration• Selection of Source

• Stable Temperature source• Master Sensors• Cold Junction Compensation• Reference Junction

• Reference Junction Units• Uncertainty Calculations• Documentation Requirement• Importance of accreditation• Calibration Report

• Calibration is the process of determining or adjusting the deviation of a

instrument (which is under calibration) with reference to a said standard.

• This is done by comparing the device or the output of an instrument to a

standard having known characteristics.

• To improve the quality of the calibration and have the results accepted by

outside organization it is desirable for the calibration and subsequent

measurement to be “traceable” to the internationally defined measurement

units.

What is calibration?

• With a new instrument.

• When a specified time period is elapsed.

• When a specified usage (operating hours) has elapsed.

• When an instrument has had a shock or vibration which potentially may have put

it out of calibration.

• Whenever observations appear questionable.

When Calibration is required

Method of Calibration

Generally contact type temperature sensor calibration can be done in two ways:

1. Primary calibration - Primary calibration is done by taking fixed points, whose

temperature remain same. E.g. Of fixed points are melting and freezing points

of water.

2. Secondary calibration - Secondary calibration is done by comparison method.

i.e. by comparing master and test sensor.

Primary Calibration

Certain systems in nature always seem to have the same temperature, for

example

• Melting Ice

• Boiling Water at sea level

• The interior of healthy human body

• Phase equilibrium points of pure material

These “landmarks” of temperature can serve as thermometric fixed points which

can be used as an apparatus for calibrating temperature sensors.

Fixed point method

• This method consists in setting up a thermometer in a fixed-point cell that provides an isothermal environment.

• The fixed point cell is a flask filled with pure material and protected by a shell. The cell is placed in an apparatus that must provide good temperature control and sufficient cell immersion to generate a uniform temperature in the measurement zone.

• The apparatus must provide for fixed-point cooling as well as controlled heat.

• Few fixed points are chosen, consistent with the need to establish a good interpolating formula.

• This method gives a highly accurate calibration and is used only for highest quality thermometry.

Maintenance apparatusfor fixed point cells

Secondary Calibration• Secondary calibration is done by comparison method. In

comparison method we need:

a.) Stable temperature source

b.) Calibrated master sensor

c.) Calibrated meter

• large numbers of thermometers can be calibrated

Simultaneously by comparison method.

• Suitable for most of the industrial calibrations.

• Comparison calibrations can be performed in a

laboratory or in the field. High accuracy can be obtained

with careful selection of equipment

Stable Temperature SourceDry Block Calibrator

• The unit consists of a special designed heating block which has located internal holes

for the probes. Although the block temperature is accurately controlled.

CALsys 1200L….300° to 1200°C

Stirred Liquid Bath

• Provide superior thermal environment for probe immersion as no air gap exist between

the probe and the medium. Thermal coupling is therefore much better. Methanol is used

for temperature below 0°C, water from 0 to 80°C and silicon oil for up to 250°C.

CALsys 650….50° to 650° C

Selection of Sources

Below are important specifications to consider when deciding on a particular temperature bath Stability: dynamic variability around a static measurement. Utopia would be when heat input minus losses equals zero for an indefinite amount of time. Always expressed as +/- of a value.

Radial Uniformity: horizontal or side to side, one point to another variation. Always expressed as a single value, no + or -.

Axial Uniformity: vertical or lengthwise, one point to another variation. Always expressed as a single value, no + or -.

Heat up and cool down time: how fast will the bath heat up to its maximum temperature and then the amount of time it takes to cool down to a safe level.

Accuracy: true or known proximity to desired setting as verified by a traceable standard of much higher accuracy. Always expressed as +/- of a value.

SSPRT : Pt100/Pt25, Temperature range 0 to 661°C

RTD : Pt100Accuracy : 1/10, 1/5, 1/3, 1/2 DIN, Class ASheath Material : SS316/ Inconel/Quartz

THERMOCOUPLE : K/N/R/SAccuracy : Special, Class 1, with option cold junction compensationSheath Material : Inconel/Ceramic (KER 710-C 799)

Master Sensors

Master Sensors

• To calibrate industrial sensors the laboratory must compare them to standard

thermometers whose characteristics have been defined and are traceable to National

Standards. Such thermometers that are traceable to national standard are known as

'Master Sensors'.

• Master sensor is used as a reference sensor in comparison type calibration process.

• Master sensor is put in the highly stable temperature zone along with sensor under

calibration, their reading is compared and error is calculated.

• Master should have high accuracy, and repeatability and should be recalibrated after

certain period of time (generally time period suggested by calibration Laboratories).

Cold Junction Compensation

• By connecting any thermocouple to measurement device three dissimilar metal

junction are created in the circuit: the thermocouple junction itself, or hot junction,

and the junction between each lead and the measurement device, or cold junctions.

• These cold junction provide their own thermoelectric voltages that are proportional

to the temperature at the device terminals.

• A technology known as cold junction compensation is therefore used to remove this

unwanted effect.

Reference Junction

• Thermocouple output is dependent of temperature of hot junction and temperature

of cold junction.

• The Cold junction temperature needs to be known to get the hot junction

temperature.

• To reduce the uncertainty of cold junction measurement Reference junction boxes

are used.

• A reference junction box terminates the thermocouple cold end at a known and

constant temperature. This can be 0° or 60° C, as per user requirement.

• The EMF of the reference junction is fixed and is added on to the output of the

thermocouple.

Reference Junction UnitsSpec / Model CalREF 0 CalREF 60

Reference Junction0°C(or Ambient -25° to 90°)

60°C(or Ambient +10° to 90°)

Accuracy +/- 0.5°C,errors can be compensatedStability +/-0.05°CStabilization time 10 MinInput J/K/T/N/S/R type thermocouple 6-24 channelControl Peltier cells + RTD + PID Heater + RTD + PIDResolution 0.1 °C

Dimension 400 H x 500 W x 200 D mm

Weight 13 kgMounting Wall mounting, 19" rack or standalone

OutputPlug/Jack or Terminals; optional temperature feedback RTD, Alram

Power supply 230 VAC/ 24 V DC

Uncertainty calculation

Uncertainty Factors Type B-Evaluation (tabular form)

source Distribution DOF Calculation Value

stability of calibration bath Rectangular infinity 0.500/1.732 0.2887

uncertainty of master sensor Normal infinity 1.000/2.000 0.5

uncertainty of precision thermometer Normal infinity 0.170/2.000 0.085

least count of precision thermometer Rectangular infinity 0.010/1.732 0.0058

Type A -Evaluation

Readings Xi Average X Xi-X Std. DevRef UUC Ref UUC Ref UUC Ref UUC993.67 994.1

993.652 994.098

0.018 0.002

0.040249 0.020494993.67 994.08 0.018 -0.018993.58 994.08 -0.072 -0.018993.67 994.1 0.018 0.002993.67 994.13 0.018 0.032

Degree of freedom : 4The standard uncertainty type A assuming Normal Probability Distribution is given by uA = 0.0205/sqrt5

= 0.0092ºCDegree of freedom = 4

FormulauA = standard deviation /sqrt(n)

Uncertainty Budget

Source ofUncertainty

Limits(°C)

Probability Distribution

Standard Uncertainty(°C)

Sensitivity Coefficient

UncertaintyContribution

Degree of freedom

X1 ±Xi Type A or Type B U (Xi) Ci °C

u1 0.5000 Rectangular 1.732 B 0.5000/1.732 1 0.2887 Infinitiveu2 1.0000 Normal 1.96 B 1.0000/2.000 1 0.5 Infinitiveu3 0.1700 Normal 1.96 B 0.1700/2.000 1 0.085 Infinitiveu4 0.0100 Rectangular 1.732 B 0.0100/1.732 1 0.0058 InfinitiveuA 0.0402 Normal Sqrt (5) A 0.0205/2.236 1 0.0092 4

Result of Uncertainty Calculation

• Combined Standard Uncertainty, Uc(°C) : 0.5837• Effective degree of freedom, Veff : 65,795,465.03• Coverage factor, K : 2.000• Expanded uncertainty, Uex (°C) : 1.4000

Formulas:

1. Uc = sqrt (uA2 +u12 +u22+u32+u42)

2. Veff = (n-1)*(Uc/uA) ^4; (n=no of observations)

3. If Veff>30 then DOF=infinitive, so K=2

4. Uex = K*Uc

Documentation Requirement

Documentation Requirement

Documentation Requirement

Documentation Requirement

Importance of AccreditationAccreditation is important in following ways:

A Recognition of Testing CompetenceLaboratory accreditation is a means of determining the technical competence of laboratories to perform specific types of testing, measurement and calibration.

A BENCHMARK FOR PERFORMANCELaboratory accreditation benefits laboratories by allowing them to determine whether they are performing their work correctly and to appropriate standards, and provides them with a benchmark for maintaining that competence

A Marketing AdvantageAccreditation is an effective marketing tool for testing, calibration and measurement organizations, and a passport to submit tenders to contractors that require independently verified laboratories.

International Recognition for LaboratoryMany countries around the world have one or more organizations responsible for the accreditation of their nation’s laboratories

Calibration Report

Quality Measured/Instruments

Temperature Range Calibration & Measurement Capability

Contact Type RTD, Thermocouples, Thermometers

-196° C 0.05° C-80° C to -38° C 0.05° C-38° C to 0° C 0.03° C> 0°C to 140°C 0.03° C> 140°C to 250°C 0.04° C> 250°C to 650°C 0.12° C> 650°C to 1000°C 1.26° C> 1000°C to 1200°C 1.26° C> 1200°C to 1600°C 2.64° C

Non Contact type Pyrometer

0°C to 100°C 1.5° C>100°C to 500°C>500°C to 1500°C>1500°C to 1700°C

2.4° C2.72° C3.27° C

>1700°C to 2700°C 5.3° C

In House Calibration Facility:Best Measurement Capabilities andtemperature range is as shown in table

Quality Measured/Instruments

Temperature Range Calibration & Measurement Capability

Calibration of SPRT/PRTS/ THERMOCOUPLES at

Triple Point of Water (0.01°C) 0.0035°C

Melting Point of Gallium (29.7646°C) 0.0070°C

Freezing Point of Tin (231.928°C) 0.0070°C

Freezing Point of Zinc (419.527°C) 0.0075°C

Freezing Point of Aluminum (660.323 °C) 0.0075°C

Fixed Point Calibration Facility

We are first private company to provide fixed point temperature calibration for Triple

point of water (Tpw), Gallium (Ga), Tin (Sn), Zinc (Zn) & Aluminum (Al) Cells.

Tempsens calibration Centres-Udaipur, Vadodara ,Bangalore

Udaipur: Tempsens Calibration CentreB-188A, Road No.5, M.I.A., Madri,Udaipur – 313003 – Rajasthan – INDIAPhone:91-294-3057724Email: lab@tempsens.com

Baroda: Tempsens Calibration CenterTF- 304, Florance classic, 10, Ashapuri Society, Near Unnati School Akota,Baroda - 390020 (Gujarat)Mob. 09327157887 Email: gujarat@tempsens.com

Bangalore: Tempsens Calibration CenterNo.7, Ist Main Coconut GardenNagarabhavil Main RoadBangalore-560072 (K.N)Mob. 09343183607Email: bangalore@tempsens.com

• Tempsens calibration centers functions as per ISO17025/NABL standards.

• Calibration of contact type sensors can be made in temperature range of -196°C to 1600°C and Calibration of non contact type sensors can be made in temperature range 0°C to 2700°C

THANK YOU!

Tempsens Instruments (I) Pvt. Ltd.B-188 A, Road No. 5, MIA, Madri Udaipur - 313 003 (Rajasthan) INDIAPhone : +91-294-3057700Fax : +91-294-3057750E-mail : info@tempsens.comWebsite : www.tempsens.com

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