Emerson Process Management 53eA Simulating Temperature, Simulating temperature, 105

MODEL 54eA	SECTION 16.0
	TROUBLESHOOTING

16.14 SIMULATING TEMPERATURE

16.14.1 General.

The 54eA controller accepts either a Pt100 RTD (for pH, 499ADO, 499ATrDO, 499ACL-01, 499ACL-02, 499ACL-03, and 499AOZ sensors) or a 22k NTC thermistor (for Hx438 and Gx448 DO sensors and most steam-sterilizable DO sensors from other manufacturers). The Pt100 RTD is in a three-wire configuration. See Figure 16-4. The 22k ther- mistor has a two-wire configuration.

16.14.2 Simulating temperature

To simulate the temperature input, wire a decade box to the analyzer or junction box as shown in Figure 16-5.

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 meas- ured 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 tempera- ture correctly if the difference between measured tempera- tures 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 cor- responds to 20.0°C. The analyzer uses 107.5 Ω to calcu- late 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 simu- lated temperatures, the analyzer is working correctly.

FIGURE 16-4. 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 16-5. Simulating RTD Inputs.

The figure shows wiring connections for sensors con- taining a Pt 100 RTD. For sensors using a 22k NTC ther- mistor (Hx438 and Gx448 sensors), wire the decade box to terminals 1 and 3 on TB6.

	Temp. (°C)	Pt 100 (Ω)	22k NTC (kΩ)
	0	100.0	64.88
	10	103.9	41.33
	20	107.8	26.99
	25	109.7	22.00
	30	111.7	18.03
	40	115.5	12.31
	50	119.4	8.565
	60	123.2	6.072
	70	127.1	4.378
	80	130.9	3.208
	85	132.8	2.761
	90	134.7	2.385
100		138.5	1.798

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