Objective To gain some understanding on the theory underlying the thermoelectric temperature measurement, especially thermocouples and develop some expertise in the measurement of temperature with thermocouples. To gain understanding on the concept of calibration and basic process of calibrating an instrument. Specifically to realize the purpose of calibration, why an instrument should be calibrated before use.
What is Thermocouple ? A thermocouple is a junction formed from two different metals that produces a voltage when subjected to a temperature difference. Thermocouples are a widely used type of temperature sensor. thermocouple Voltage (electromotive force) emf The temperature difference T is converted to voltage (electromotive force)
Functional form Where :is the type of thermocouple. is the temperature at measuring junction of the thermocouple. is the temperature at the reference junction of the thermocouple. is the electromotive force (voltage).
Type of Thermocouples TypeMaterialsTemperature RangeSensitivity EChromel (Ni-Cr) & Constantan (Cu-Ni) -270 to 1000 ° C 60.9 μV/°C JIron & Constantan (Cu- Ni) -210 to 1200 ° C51.7 μ V/ ° C KChromel (Ni-Cr) & Alumel (Ni-Al) -270 to 1350 ° C40.6 μ V/ ° C TCopper & Constantan (Cu- Ni) -270 to 400 ° C40.6 μ V/ ° C RPlatinum & 87%Platinum -50 to 1750 ° C6 μ V/ ° C S90% Platinum & 10% Rhodium -50 to 1750 ° C6 μ V/ ° C B94% Platinum & 6% Rhodium -50 to 1750 ° C6 μ V/ ° C
Calculation of Uncertainty Since the information of the voltmeter and hot bath are unknown, so Let And, So, Note : For and @ 95% confidence : ** ** Reference : Inverse Student t Distribution; “Some Aspect of Experimentation”,2103-390 Mechanical Engineering Experimentation and Laboratory I, Asi Bunyajitradulya (Page 193).