Emerson Rosemount5081, Instruction Manual, Page: 127 / 152

Three-wire RTD configuration Figure 8-14:
Although only two wires are required to connect the RTD to the analyzer, using a third wire allows the
analyzer to correct for the resistance of the lead wires and for changes in the lead wire resistance with
temperature.
Simulating temperature procedure
To simulate the temperature input, wire a decade box to the analyzer or junction box as
shown in
Figure 8-15 .
Simulating RTD inputs Figure 8-15:
The figure shows wiring connections for sensors containing a Pt 100 RTD. For sensors using a 22k NTC
thermistor (Hx438 and Gx448 sensors), wire the decade box to terminals 1 and 2 on TB6.
To check the accuracy of the temperature measurement, set the resistor to 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 controller is
measuring temperature correctly if the difference between measured temperatures
equals the difference between the values in the table to within ±0.1 °C.
Diagnostics and troubleshooting
Instruction Manual 117