Emerson Rosemount MCL-220 Manual page 84

Troubleshooting
Figure 9-4:
To check the accuracy of the temperature measurement, set the resistor simulating the
RTD to the values indicated in the table and note the temperature readings. The measured
temperature might not agree with the value in the table. During sensor calibration, an
offset might have been applied to make the measured temperature agree with a standard
thermometer. The offset is also applied to the simulated resistance. The MCL is measuring
temperature correctly if the difference between measured temperatures equals the
difference between the values in the table to within ±0.1 °C.
For example, start with a simulated resistance of 103.9 Ω, which corresponds to 10.0 °C.
Assume the offset from the sensor calibration was -0.3 Ω. Because of the offset, the
transmitter calculates temperature using 103.6 Ω. The result is 9.2 °C. Now change the
resistance to 107.8 Ω, which corresponds to 20.0 °C. The transmitter uses 107.5 Ω to
calculate the temperature, so the display reads 19.2 °C. Because the difference between
the displayed temperatures (10.0 °C) is the same as the difference between the simulated
temperatures, the transmitter is working correctly.
Temp. (°C)
0
10
20
25
30
40
50
60
70
80
76
Simulating RTD Inputs
Pt 100 (Ω)
100.0
103.9
107.8
109.7
111.7
115.5
119.4
123.2
127.1
130.9
Rosemount MCL