Emerson 51-DO-04, 51-DO-03 instruction manual Simulating Temperature, Simulating temperature

MODEL DO-03/04	SECTION 10.0
	TROUBLESHOOTING

10.7 SIMULATING TEMPERATURE

10.7.1 General.

The 54eA analyzer accepts a Pt100 RTD. The Pt100 RTD is in a three-wire configuration. See Figure 10-2.

10.7.2 Simulating temperature

To simulate the temperature input, wire a decade box to the analyzer or junction box as shown in Figure 10-3.

To check the accuracy of the temperature measurement, set the resistor simulating the RTD to the values indicat- ed 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 tem- perature 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 analyzer 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 analyzer uses 107.5 Ω to cal- culate the temperature, so the display reads 19.2°C. Because the difference between the displayed tempera- tures (10.0°C) is the same as the difference between the simulated temperatures, the analyzer is working correctly.

FIGURE 10-2. Three-Wire RTD Configuration.

Although only two wires are required to connect the RTD to the analyzer, using a third (and sometimes fourth) wire allows the analyzer to correct for the resistance of the lead wires and for changes in the lead wire resistance with temperature.

FIGURE 10-3. Simulating RTD Inputs.

The figure shows wiring connections for sensors con- taining a Pt 100 RTD.

Temp. (°C)	Pt 100 (Ω)
0	100.0
10	103.9
20	107.8
25	109.7
30	111.7
40	115.5
50	119.4
60	123.2
70	127.1
80	130.9
85	132.8
90	134.7
100	138.5

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