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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.
Temp. (°C) Pt 100 (
ΩΩ
)
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
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.