2 ObjectiveTo 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 calibratingan instrument. Specifically to realize the purpose of calibration, why an instrumentshould be calibrated before use.
3 (electromotive force) emf 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.thermocoupleThe temperature difference DT is converted to voltage (electromotive force)Voltage(electromotive force) emf
4 Functional form Where : is the type of thermocouple. is the temperature at measuring junctionof the thermocouple.is the temperature at the reference junctionis the electromotive force (voltage).
5 Type of Thermocouples Type Materials Temperature Range Sensitivity E Chromel (Ni-Cr) & Constantan (Cu-Ni)-270 to 1000°C60.9 μV/°CJIron & Constantan (Cu-Ni)-210 to 1200°C51.7 μ V/°CKChromel (Ni-Cr) & Alumel (Ni-Al)-270 to 1350°C40.6 μ V/°CTCopper & Constantan (Cu-Ni)-270 to 400°CRPlatinum & 87%Platinum-50 to 1750°C6 μ V/°CS90% Platinum & 10% RhodiumB94% Platinum & 6% Rhodium
15 Thermocouple Ref. Table Calibration Result Voltage (mV) Thermocouple Type KTemperature (°C)Thermocouple Ref. TableCalibration ResultVoltage (mV)Average Voltage (mV)SD1st2nd40.1580.080.060.07070.27188.8.131.52100.3970.310.330.320130.5170.450.450160.6370.560.560190.7580.690.700.695220.8790.810.770.790251.0000.930.950.940281.1221.071.070311.24184.108.40.206341.3661.311.331.320371.4891.431.451.440401.6121.531.530431.7351.681.661.670461.8581.791.821.805491.9821.931.951.940522.1062.042.062.050552.2302.162.192.175582.3542.292.312.300612.4782.402.452.425
24 Calculation of Uncertainty Since the information of the voltmeter and hot bath are unknown, soLetAnd,So,Note : For and @ 95% confidence : **** Reference : Inverse Student t Distribution; “Some Aspect of Experimentation”, Mechanical Engineering Experimentation and Laboratory I, Asi Bunyajitradulya (Page 193).