TEMPERATURE CALIBRATION TRAINING

TURKISH STATE METEOROLOGY SERVICE 

CALIBRATION CENTER 

TEMPERATURE CALIBRATION 

TRAINING 

Hamza A. CESSUR 

Temperature&Humidity Calibration Laboratory 

Calibration Center – TSMS – 2011 

1

CONTENT OF PRESENTATION 

1. Temperature Concept & Hystory of Thermometry 

2. Thermometer Types 

3. Definitions for Calibration Terms 

1. Metrology, Calibration, Adjustment, Reference 

Standard, Working Standard, Traceability, 

Uncertainty, Accuracy, Stability, Repeatability, 

Measurement error, Drift 

4. Calibration Equipments and Setup 

1. Reference standards 

2. Calibration mediums 

3. Data acquisition units 

5. Temperature Calibration Methods 

1. Fixed point 

2. Comparison 

Calibration Center – TSMS – 2011

TEMPERATURE CONCEPT 

� Temeperature is a measure of 

average kinetic energy 

� State parameter 

� Not directly measurable 

t1 

Calibration Center – TSMS – 2011 3 

t2 

t3 t4 

t # t1+t2+t3+t4 ! 

� To be able to measure the temperature, we have to use a 

thermometer which has some physical features changing 

with temperature in a reliable way and the changes 

should be reproducable. 

� Everyone have a different understanding on what is cold or 

hot.

IMPORTANCE OF 

TEMPERATURE MEASUREMENT 

Correct measurement of temperature has a vital importance 

for daily activities: 

�Medical activities, 

�Industrial processes, 

�Manufacturing, 

�Weather forecasting, etc. 

� Input to NWP 


4

HYSTORY OF THERMOMETRY 

� First modern thermometer ever known was made by 

Galilei and Santorio in the 16th century and it is called 

as thermoscope. 


5

FIRST LIQUID IN GLASS THERMOMETERS 

� After that, two scientists Celsius ve Fahrenheit, produced 

liquid in glass thermometers using melting point of pure 

ice and boiling point of water as reference points to make 

the accuracy better. 

Anders CELSIUS 

(1701-1744) (Swedish) 


Daniel Gabriel FAHRENHEIT 

(1686-1736) (German) 

6

THE KELVIN UNIT 

� The basis for temperature scale was introduced by the 

Physicist, Lord Kelvin (Scottish) in 1854. 

� This scale is based on the “absolute zero” point at 

which there is no any visible energy. And it is used by 

physicists for determination and implementation of 

fundamental rules of thermodynamics. 

� By international agreement, absolute zero is defined 

as 0 K on the Kelvin scale and as −273.15°C on the 

Celsius scale. 


7

TEMPERATURE UNITS 

� Any temperature is the difference from the 

temperature of freezing point of water (273.15 

Kelvin(K) ). T is thermodynamic temperature and t is 

temperature in degrees of Celsius. 

� t / °C = T / K - 273.15 

� Symbol of Celsius unit is °C, and is equal to Kelvin as 

difference temperature. 


8

TEMPERATURE UNITS 

� Another temperature unit commonly used by 

England and USA is Fahrenheit (°F). 

� °F = (1.8 x °C) + 32 

� NOTICE! ° (degree) symbol is used for Celsius and 

Fahrenheit temperatures (°C, °F). Not used for 

Kelvin. 

°K – wrong …… K – correct 


9

TRIPLE POINT OF WATER 

� The unit of thermodynamics was 

accepted as Kelvin in 1954, and is 

defined as 1/273,16 of 

thermodynamic temperature of 

triple point of water. 

� Triple point of water is the 

balanced 3 states of water (solid, 

liquid and gas) being together at 

the same time and medium. He 

temperature of at this point is a 

little above of the melting point 

of pure water (0,01°C / 273,16 

K). 


10

TEMPERATURE SCALE 


� Starting from TPW, it is 

possible to build a 

temperature scale by 

using gas and radiation 

thermometers suitable to 

well-kown physical rules. 

11

TEMPERATURE SCALE 

� Although realizing the fixed 

points is not simple and not 

possible at any time, very 

accurate results was obtained 

for several fixed points like very 

high temperatures for freezing 

point of metals and very low 

temperatures for triple point of 

gasses. 


Setting up a fixed-point cell 

Setting up the gold freezing point at 

NPL 

12

CALIBRATION IN FIXED POINTS 

� By inserting these fixed points to 

international temperature scale, it 

has been possible to calibrate 

Standard Platinum Resistance 

Thermometers (SPRT) and Radiation 

Thermometers with a high 

reproducibility. 


13

FIXED POINTS AS NATIONAL STANDARDS 

� Fixed points cells existing in the national 

metrology labs are regularly compared to 

other national fixed point standards. 

� In this way, temperature standards all 

over the world are up-to-date and 

permanent. 


14

ITS-90 

(INTERNATIONAL TEMPERATURE SCLAE-1990) 


� ITS-90 (International 

Temperature Scale- 

1990), has been adopted 

at the BIPM 

(International Bureau of 

Weights and Measures) 

in 1987. 

15

ITS-90 

(INTERNATIONAL TEMPERATURE SCLAE-1990) 


16

THERMOMETER TYPES 

� Resistance thermometers 

� Thermocouple thermometers 

� Liquid in glass thermometers 

� Radiation thermometers 


17

RESISTANCE THERMOMETERS 


� An electrical 

thermometer produced 

according to the 

variability of resistance of 

a metal wire with 

temperature. 

18

RESISTANCE THERMOMETERS 

� Metal wires may be platinum(Pt), nickel(Ni) 

or copper(Cu). 

� May have an accuracy of 0,001°C in case of 

using them with high quality measurement 

units. 

� Measurement range: -270°C to 962°C 


19

Temperature-measuring instrument consisting of 

two wires of different metals joined at each end. 

One junction is placed where the temperature is to 

be measured, and the other is kept at a constant 

lower (reference) temperature. A measuring 

instrument is connected in the electrical circuit. 

The temperature difference causes the 

development of an electromotive force that is 

approximately proportional to the difference 

between the temperatures of the two junctions. 

Temperature can be read from standard tables, or 

the instrument can be calibrated to display 

temperature directly. 

�Measurement range: 

THERMOCOUPLE THERMOMETERS 

-270 to 2,320 °C 20 


LIQUID IN GLASS THERMOMETERS 

Working according to principle of expansion of a liquid with rising of 

temperature. 

The height of a liquid in a closed glass tube changes with the change 

in the temperature applied to it. A scale is marked onto it according 

to result of the calibration of thermometer. 

Most common used liquid is mercury. Alcohol is also commonly used. 

Has being used in science, medicine, metrology and industry 

applications for 300 years. 


21

RADIATION THERMOMETERS 

Measures temperature using blackbody radiation (generally infrared) 

emitted from objects. 

They are sometimes called laser thermometers if a laser is used to help 

aim the thermometer, or non-contact thermometers to describe the 

device’s ability to measure temperature from a distance. 

By knowing the amount of infrared energy emitted by the object and its 

emissivity, the object's temperature can be determined by using Planck’s 

Law. 


22

METROLOGY 

- Field of knowledge concerned with measurement 

- Metrology includes all theoretical and practical aspects of measurement, 

whichever the measurement uncertainty and field of application. 

CALIBRATION 

a.operation establishing the relation between quantity values provided by 

measurement standards and the corresponding indications of a 

measuring system, carried out under specified conditions and including 

evaluation of measurement uncertainty 

b.operation that establishes the relation, obtained by reference to one or more 

measurement standards, that exists under specified conditions, between 

the indication of a measuring system and the measurement result that 

would be obtained using the measuring system 


ADJUSTMENT 

set of operations carried out on a measuring system in order that it provide 

prescribed indications corresponding to given values of the quantity to be 

measured 

NOTE 

Adjustment of a measuring system should not be confused with calibration of a 

measuring system. 

MEASUREMENT UNCERTAINTY 

parameter that characterizes the dispersion of the quantity values that are 

being attributed to a measurand, based on the information used. 

NOTE 

Every measurement has an uncertainty value contributed to the result. 

EXAMPLE 

Calibration result: Test device indicates 21.0 0 C ± 0.1 0 C at 20.0 0 C 


ACCURACY 

closeness of agreement between a quantity value obtained by measurement 

and the true value of the measurand 

NOTES 

1 Accuracy cannot be expressed as a numerical value. 

2 Accuracy is inversely related to both systematic error and random error. 

3 The term ‘accuracy of measurement’ should not be used for trueness of 

measurement and the term ‘measurement precision’ should not be used for 

“accuracy of measurement”. 

STABILITY 

ability of a measuring system to maintain its metrological characteristics 

constant with time 

DRIFT 

change in the indication of a measuring system, generally slow and 

continuous, related neither to a change in the quantity being measured nor 

to a change of an influence quantity 


REPEATABILITY 

property of a measuring system to provide closely similar indications for 

replicated measurements of the same quantity under repeatability 

conditions 

NOTE 

Repeatability can be expressed quantitatively in terms of the dispersion 

parameters of the indications of the measuring system. 

ERROR OF MEASUREMENT 

difference of quantity value obtained by measurement and true value of the 

measurand 


PRIMARY STANDARD 

measurement standard whose quantity value and measurement 

uncertainty are established without relation to another measurement 

standard for a quantity of the same kind 

-TPW (any standard highest in the calibration hierarchy) 

SECONDARY STANDARD 

measurement standard whose quantity value and measurement 

uncertainty are assigned through calibration against, or comparison 

with, a primary standard for a quantity of the same kind 

- SPRT (calibrated in TPW) 


REFERENCE STANDARD 

measurement standard used for the calibration of working standards in a 

given organization or at a given location 

- Highest level standard for any specific laboratory. (SPRT for us) 

WORKING STANDARD 

measurement standard that is used routinely to calibrate, verify, or check 

measuring systems, material measures, or reference materials 

- Usually calibrated with a reference measurement standard. 

TRAVELLING STANDARD 

measurement standard, sometimes of special construction, intended for 

transport between different locations 

- Standards used for ILCs. 






Alcohol -110 to 100°C 

Mercury -38 to 650 °C 

Mercury-thalium -56 to 650 °C



Time stability: following an acquisition during a long time 

temperature (°C) 

16:33:36 

0 

-0.01 

-0.02 

-0.03 

-0.04 

-0.05 

-0.06 

-0.07 

-0.08 

-0.09 

-0.1 

16:40:48 

16:48:00 

16:55:12 

17:02:24 

17:09:36 

hour 

17:16:48 

TLH 600 3439 


17:24:00 

Stability at 0°C of a bath 

17:31:12 

17:38:24

SPRT 

� Spatial homogeneity; with two instruments of the same type (calibrated) 

45 cm 

30 cm 

21 cm 

BATH 

PT100 

7 cm 

14 cm 


CALIBRATION METHODS 

LEVEL INSTRUMENT METHOD 



A. CALIBRATION AT FIXED POINTS 

Resistance 

thermometer 

DATA 

ACQUISITION 

UNIT 

� Resistance values of the thermometer are measured 

� Resistance ratios (W(T)) with respect to resistance value at TPW are calculated 

� Reduced resistances (W R (T)) are calculated according to ITS-90 reference functions 

� Calibrations coefficient to transform resistance into temperature are calculated 


Interpolating function 

� Temperatures are determined in terms of the ratio of resistance R(T90 ) at 

temperature T90 and the resistance R(273.16K) at the triple point of water: 

R( 

T90) 

W ( T90) 

� 

R( 

273. 

16K 

) 

� Reference function W r (T 90 ) is defined: 

Range from 13.8033 K to 273.16 K Range from 273.16 K to 1234.94K 

ln 


12 

�W r ( T90) 

� � A0 

� � 

i�1 

: � � T90 

� � 

�ln� 

� �1. 

5� 

� 

� 273. 

16 

A � 

� 

i 

� 

� 1. 

5 � 

� 

� 

� 

� 

Numeric values of reference function coefficients (Ai, Ci) and inverse reference function (Bi, 

Di) are available in literature. 

� Deviation function is a deviation of reference function Wr (T90 ) and ratio 

W(T90 ) is defined: 

� 

i 

W 

( T 

W r 

( T90) 

� W ( T90) 

�W 

( T90) 

90 

) � C 


r 

0 

� 

9 

� 

i�1 

C 

i 

T 

� 

� 

� 90 � 

� 

754. 

15� 

481 

� 

� 

i 

39


Interpolating function 

The forms of deviation function differ according to different temperature 

range and used fixed points. In the temperature range from 13.8033 K 

to 1234.94 K three forms of deviation function are defined: 

• from 83.8058 K to 273.16 K: 

�W ( T ) �1� 

� b ��W 

( T ) �1� 

ln�W 

( T ) � 

�W 

( T90 

) � a � 90 

90 � 

90 

• from 273.15 K to 1234.94 K: 

90 

� � � � � � � �2 2 

3 

W ( T ) �1 

� b � W ( T ) �1 

� c � W ( T ) �1 

� d � W ( T ) �W 

( 660. 

323 ) 

�W 

( T ) � a � 

�C 

90 

90 

Values of coefficients a, b, c, c i , d depends on temperature range and 

fixed point used in calibration. 


90 

90


B. CALIBRATION WITH COMPARISON METHOD 

(working standard calibration) 

• Check the instrument to decide if it is suitable for calibration 

• Label the instrument to make a difference mark from any other device 

• Instrument should rest in the laboratory conditions for to adopt 

• All instrument and calibration certificates sould be ready for use 

• Make the necessary arrangements setting up the calibration 


DATA 

ACQUISITION 

UNIT 

(MULTIMETER) 




Resistance 

thermometer 

SPRT 

� At least 5 calibration points (-40, -20, 0, 25, 50 °C). 

� Liquid calibration bath or climatic chamber as calibration medium. 

� Using multimeter or resistance thermometer readout unit for data acquisition. 

� Measurements start with with zero point (ice-point bath) and finishes the same. 

� Other calibration points should be decided accordind to usage range. 

� Measure the resistances against reference temperatures. 

� Stable values are needed for an appropriate calibration. 


� Connection type of RT should be considered 

� 2, 3, or 4 wires

� Resistance values of the thermometer are measured against ref. temp. 

� The Callendar–Van Dusen equation is an equation that describes the relationship 

between resistance (R) and temperature (t) of platinum resistance thermometers. 

� Calculate A,B , C coefficients using Callendar-Van Dusen Equations. 

� For the range between -200 °C to 0 °C the equation is; 

R(t) = R(0)[1 + A * t + B * t 2 + (t − 100)C * t 3 ]. 

�For the range between 0 °C to 661 °C the equation is; 

R(t) = R(0)(1 + A * t + B * t 2 ). 

� Calibrations coefficient (A,B,C) to transform resistance into temperature are 

calculated. 





B. CALIBRATION WITH COMPARISON METHOD (thermometer with display) 

DISPLAY 


BATH 

READ 

OUT 

� Calibration points should be decided accordind to usage range. 

� Measurements start with zero point and finishes the same. 

� Liquid calibration bath or climatic chamber as calibration medium. 


Test thermometer 

Reference thermometer 

� Comparison of reference temperature against temperature of calibrated device. 

� Stabilization of temoeratures (medium, reference standard and calibrated thermometer) 

� Take the measurements and record them.


� Parameter that characterizes the dispersion of the quantity values that are 

being attributed to a measurand, based on the information used. 

NOTE: Every measurement has an uncertainty value contributed to the result. 

EXAMPLE: Calibration result: Test device indicates 21.0 0 C ± 0.1 0 C at 20.0 0 C 

� A measure of the possible error in the estimated value of the measurand as 

provided by the result of a measurement 

� An estimate characterizing the range of values within which the true value 

of a measurand lies 

� The uncertainty of the result of a measurement reflects the lack of exact 

knowledge of the value of the measurand 

� The result of a measurement after correction for recognized systematic effects is 

still only an estimate of the value of the measurand because of the uncertainty 

arising from random effects and from imperfect correction of the result for 

systematic effects. 





In practice, there are many possible sources of uncertainty in a measurement, 

a) incomplete definition of the measurand; 

b) imperfect realization of the definition of the measurand; 

c) nonrepresentative sampling – the sample measured may not represent the 

defined measurand; 

d) inadequate knowledge of the effects of environmental conditions on the 

measurement or imperfect measurement of environmental conditions; 

e) personal bias in reading analogue instruments; 

f) finite instrument resolution or discrimination threshold; 

g) inexact values of measurement standards and reference materials; 

h) inexact values of constants and other parameters obtained from external 

sources and used in the data-reduction algorithm; 

i) approximations and assumptions incorporated in the measurement method 

and procedure; 

j) variations in repeated observations of the measurand under apparently 

identical conditions. 



SOURCE OF UNCERTAINTY 

ESTIMATE 

D VALUE DISTRIBUTION DENOMINATOR 


STANDARD 

UNCERTAINTY COEFFICIENT 

PARTIAL 

VARIANCE 

( 0 C^2) 

Uncertainty of reference (°C) 0,0030 normal 2 0,0015 1 0,00000225 

Resolution of reference(Ω) 0,00005 Rectangular 1,73 0,00003 9,804 0,00000009 

Drift of reference (Ω) 0,0019 Rectangular 1,73 0,0011 9,804 0,00011566 

Repeatability of reference(Ω) 0,00011 normal 1 0,00011 9,804 0,00000116 

Uncertainty of multimeter(Ω) 0,0011 normal 2 0,0006 9,804 0,00002908 

Homgeniety of calibration bath(°C) 0,0150 Rectangular 1,73 0,0087 1 0,00007500 

Uncertainty of ice-bath(°C) 0,0200 normal 2 0,0100 1 0,00010000 

Other parameters (pers., etc.)(°C) 0,0018 Rectangular 1,73 0,0011 1 0,00000121 

Resolution of test thermometer (°C) 0,0050 Rectangular 1,73 0,0029 1 0,00000833 

Repeatability of test thermometer (°C) 0,0050 normal 1 0,0050 1 0,00002500 

Hysteresis of test thermometer (°C) 0,0100 Rectangular 1,73 0,0058 1 0,00003333 

Uncertainty of interpolating function(°C) 0,0100 normal 1 0,0058 1 0,00003333 

Combined 

Uncertainty 0,021 

Expanded 

Uncertainty 0,042 °C

TEMPERATURE CALIBRATION TRAINING

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