Thermocouple Noise Calculation Example - Data Translation DT9828 User Manual

Appendix A

Thermocouple Noise Calculation Example

Assume that you are using a type K thermocouple to measure a temperature of approximately
100°C, and the DT9828 module is configured to use a throughput rate of 600 Samples/s and
the moving average filter. The steps to determine the maximum expected measurement noise
are as follows:
1. Determine the CJC noise at the stated throughput rate and filter setting. From
2. Determine the input voltage noise at the stated throughput rate and filter setting. From
3. Determine the sensitivity of the specified thermocouple type at the measurement
4. Calculate the equivalent temperature noise by dividing the input voltage noise by the
5. To determine the total noise, add the CJC sensor noise to the equivalent temperature noise
98
the CJC noise is 0.01°C pk-pk for a throughput rate of 600 Samples/s and the moving
average filter.
25, the voltage noise is 3 μV pk-pk for a throughput rate of 600 Samples/s and the
Table
moving average filter.
temperature. From the NIST Thermocouple Reference Tables, the sensitivity of a Type K
thermocouple at 100°C is 41.5 μV/°C.
sensitivity of the thermocouple:
3 μV pk-pk / 41.5 μV/°C = 0.072°C pk-pk
of the input voltage noise. The total temperature noise is as follows:
0.01°C pk-pk + 0.072°C pk-pk = 0.082°C pk-pk
Table 25,