Measuring MOSE with Omega software

Omega software with suitable multimeter (such as Keithley 2000 with 10 channel switch) can be used to measure all required properties and to calculate the final pO2. Instrument will measure two voltages and a resistance in rapid sequence. From the resistance the software will calculate cold junction compensation; and use the thermocouple voltage and sensor voltage to solve the Nernst equation for the pO2 with built-in function for MOSE.

The function to calculate and plot the pO2 (fraction of pure O2 at atmospheric pressure) in Omega is MOSE(T,E,A,B) where

- T is sensor temperature in Celsius
- E is sensor voltage (with odd results change the polarity)
- A calibration factor Ax from supplied excel sheet (in cell E54)
- B calibration factor Bx from supplied excel sheet (in cell E55)

To solve for temperature one can use TCS and TT2 functions explained further in the Omega manual. TT2 converts thermistor resistance to temperature; this is our cold junction compensation. TCS solves for S type thermocouple temperature.

TT2(10000)

Thermistor has roughly 10 000 ohms at room temperature, so the above gets evaluated to 25, or to your ambient temperature when you use the resistance measured from the thermistor. The thermistor should be located where the thermocouple ends and identical measurement wires start.

TSC(0.005, 25)

First parameter is the thermocouple voltage, second is the cold junction compensation in Celsius. In this case the above would evaluate to 590°C (565 from the thermocouple voltage and 25 from the cold junction compensation).

Final expression

End result would look something like MOSE(TSC($N1.MV, TT2($N2.M2)), $N3.MV, A, B) where E is replaced with sensor voltage e.g. $N3.MV, A and B are the calibration factors. Node 1 is sensor thermocouple voltage, Node 2 is resistance of the thermistor located at the end of the thermocouple compensation cables, used as cold junction compensation, and Node 3 is the sensor voltage.