Data Translation DT9828, User Manual

Page: 98 / 116

Appendix A
98
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 Table 25 ,
the CJC noise is 0.01°C pk-pk for a throughput rate of 600 Samples/s and the moving
average filter.
2. Determine the input voltage noise at the stated throughput rate and filter setting. From
Table 25 , the voltage noise is 3
μ
V pk-pk for a throughput rate of 600 Samples/s and the
moving average filter.
3. Determine the sensitivity of the specified thermocouple type at the measurement
temperature. From the NIST Thermocouple Reference Tables, the sensitivity of a Type K
thermocouple at 100°C is 41.5
μ
V/°C.
4. Calculate the equivalent temperature noise by dividing the input voltage noise by the
sensitivity of the thermocouple:
3
μ
V pk-pk / 41.5
μ
V/°C = 0.072°C pk-pk
5. To determine the total noise, add the CJC sensor noise to the equivalent temperature noise
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