Temperature Control System for Temperature Sensor
Calibration
Chatchaval Pornpatkul1* Satean Tanyasrirat1 and Jongkol Ngamwiwit2
1

Department of Instrumentation and Control Engineering, Faculty of Engineering,
Pathumwan Institute of Technology, Bangkok, Thailand

2

Department of Instrumentation and Control Engineering, Faculty of Engineering,
King Mongkut's Institute of Technology Ladkrabang, Bangkok, Thailand

1.

Introduction
Temperature is the physical quantity of the heating/coolingthat is familiar in everyday life. The temperature measurement
has been performed firstly in the medical community bytouching a hand to a patient for analysis. In the manufacturingindustry, several sensors have also been developed
continuously in order to measure the temperature. Recently, thetemperature sensors used in the process of temperature
measurement are the industrial platinum resistance thermometer(IPRT), resistance temperature detector (RTD), thermocouple(TC) and thermistor, which are commonly employed in theindustry. However, the temperature sensors are needed tocalibrate by using temperature control calibration. The satisfied
qualifications of the calibration compose of evaluation test andaccuracy test.
In this paper, a temperature process control for temperature
sensor calibration is proposed. The water temperature iscontrolled not exceed ±0.5°C (expanded uncertainty) in therange of ambient temperature up to 90°C. In accordance withthe guidelines of the international temperature scale 1990; ITS90, the temperature sensor, ie., thermocouple is tested. In orderto show the capability of the proposed temperature processcontrol at 40°C and 60°C, the calibration result of TC iscompared with the standard platinum resistance thermometer(SPRT).
2Temperature Source
Temperature Source means a temperature control system
for temperature sensor calibration. The temperature sensor
calibration in industrial and laboratory calibration can be madein the working standard temperature in the range of ambient
temperature up to 90°C using water as the medium. There are
two major components of the temperature process control
consisting of heating and cooling system.
The temperature process control system in the laboratory is
shown in Fig. 1 and it will be used for temperature sensor
calibration. In order to design a controller, the transfer functionof the temperature process must be known first and it can beobtained from the experiment as shown in Fig. 2.

Fig. 2 Reaction curve of temperature process for 60 C .
After drawing the tangent line to the arc of reaction curve,
the transfer function of the process is
G p ( s) Kp e Lp s(1) s  1
pwhere K p  0.932 istheprocess

dynamicgain,

Lp  0.75min is the effective process dead time (min) and p  160min is the effective process time constant (min).
These values are summarized in Table 1.
3. Temperature Control System and Its Capability TestingIn this section, the proposed temperature control system andits capability testing will be described.
3.1 Temperature Control System
The proposed temperature control system with PI controller
is shown in Fig. 3, where Gc ( s) and Gp ( s) are the transfer
function of PI controller and the temperature process for Fig. 1
respectively.
G p ( s)Gc (s) (s)SV ( s )-100 1 
1 
Pb  Ti s MV ( s )Kp e

 Lp sPV ( s ) s  1
pPV ( s )Fig. 3 Temperature control system with PI controller.
The obtained reaction curve shown in Fig. 1 is used find theproportional Pb and integral time Ti of PI controller by Dahlin
Fig. 1 Temperature process control experiment.

Algorithm [1].

From Dahlin algorithm, controller gain K c can be foundfrom Pb  100 K p   L

pcp



6 test points

where  c is assigned to be equal×

to 0.3 sec. Hence, Pb  93.38% and Ti   p  160min.

××oreference point×

Table 1 Parameters of the process and controller
ParameterKp

pLp

G p ( s)0.938

1600.75--Gc (s)---93.38%=1.07

160

Pb =100/Kc

Ti

The responses of PI temperature control system at 40 C and60 C are shown in Fig. 4 and Fig. 5 respectively.

××Fig. 6 Evaluation method.
Table 2 Evaluation test at 40 C
M1
M2
M3
39.9
40.2
40.3
39.9
40.2
40.1
40.0
40.2
40.1

M4
39.3
40.3
40.2

M5
40.3
40.2
40.2

M6
40.2
40.1
40.1

Table 3 Evaluation test at 60 C
M1
M2
M3
60.2
60.2
60.2
60.3
60.1
60.3
60.2
60.2
60.2

M4
60.2
60.4
60.3

M5
60.2
60.2
60.2M6
60.1
60.2
60.1

3.2.2 Accuracy TestIn order for temperature controller must be used theStandard Thermometer, in this research we used the Standard
Platinum Resistance Thermometer; (SPRT) for determination
the characteristic and error of Temperature Controller in thiscase, diameter of SPRT < 6mm which do not calculated heat
conduction [ITS-90]

Fig. 4 Response at 40 C.

4. Estimation of the Expanded Uncertainty of Measurement
EURAMET/cg-13/v.01 for guide line to calibration. The
repeatability of the predicted temperature values is expressed asthe uncertainty. The total expanded at reference temperature(23°C±2°C) associated with the temperature measurement at
95% confidence level for the Temperature Controller forCalibration unit is estimated to be :U  k  uC

(2)

From the experimental results and by using equation (2), thecalibration for expanded uncertainty[3] not over than 0.5 C .
Hence, the temperature process control proposed in this paper
can be used for calibrating temperature sensors.
5.
Fig. 5 Response at 60 C.

Conclusions
In this study, temperature control system can be designedthat are suitable to be used as a tool for measuring temperaturein the calibration of working standard.

3.2 Capability Testing
It is necessary to test the capability of the proposed control
system before performing the calibration. There are evaluation
test[2] and accuracy test.

References[1] Zhang Zhi-Gang, Zou Ben-Guo and Bi Zhen-Fu, Dahlin

3.2.1 Evaluation Test
Two temperature sensors are used for evaluation test. FromFig. 4, the sensor 1 measures temperature at reference point
located at the center of process tank and the sensor 2 measures
the temperature at test point (6x3 points are measured). Two setof the measured value are summarized in Table 2 and Table 3for temperature at 40 C and 60 C respectively. The different
values from the reference value are evaluated to find stability
and uniformity of temperature source (the calibration capabilityof the proposed control system).

international conference on Chinese control and decisionalgorithm design and simulation for time-delay system,
Proceeding CCDC'09 Proceedings of the 21st annual
conference, Pages 5849-5852, IEEE Press Piscataway, NJ,
USA ©2009.
[2] EURAMET/cg-13/v.01 for guide line to calibration,2005.
[3] Guide to the Expression of Uncertainty in Measurement(GUM), first edition, 1995, ISBN 92-67-10188-9.