Emerson Rosemount TCL - 9.3 Calibrating total chlorine; Chapter 10 Maintenance; 10.1 Transmitter

Figure 13-3: Three-Wire RTD Configuration
A. Resistance temperature device
B. Resistance temperature device in
C. Resistance temperature device sense
D. Resistance temperature device return
Although only two wires are required to connect the resistance temperature device to the
transmitter, using a third (and sometimes fourth) wire allows the transmitter to correct for
the resistance of the lead wires and for changes in the lead wire resistance with
temperature.
13.8.2 Simulating temperature
To simulate the temperature input, wire a decade box to the transmitter as shown in
Figure 13-4.
Figure 13-4: Simulating Resistance Temperature Device Inputs
A. Resistance temperature device return
B. Resistance temperature device sense
C. Resistance temperature device in
D. Resistance temperature device shield
To check the accuracy of the temperature measurement, set the resistor simulating
the resistance temperature device 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 transmitter 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.
Temperature (°C)
Pt 100 (Ω)
0 100.0
10 103.9
20 107.8
Reference Manual Troubleshoot
00809-0200-3415 January2023
Rosemount TCL 56 71