Instruction manual

96
MODEL Xmt-P SECTION 10.0
TROUBLESHOOTING
10.7.3 Simulating pH input when the preamplifier is in a junction box.
The procedure is the same as described in Section 10.7.2. Keep the connections between the analyzer and the junction
box in place. Disconnect the sensor at the sensor side of the junction box and connect the voltage source to the sensor
side of the junction box. See Figure 10-3.
10.7.4 Simulating pH input when the preamplifier is in the sensor.
The preamplifier in the sensor converts the high impedance signal into a low impedance signal without amplifying it. To
simulate pH values, follow the procedure in Section 10.7.2.
10.8 SIMULATING TEMPERATURE
10.8.1 General.
The Xmt-P transmitter accepts either a Pt100 RTD, Pt1000 RTD, or
a 22k NTC thermistor (for Hx338 and Hx348 pH sensors). The
Pt100 RTD is in a three-wire configuration. See Figure 10-2. The
22k thermistor has a two-wire configuration.
10.8.2 Simulating temperature
To simulate the temperature input, wire a decade box to the ana-
lyzer 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 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 cor-
rectly 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 calibra-
tion was -0.3 Ω. Because of the offset, the analyzer calculates tem-
perature using 103.6 Ω. The result is 9.2°C. Now change the resist-
ance to 107.8 Ω, which corresponds to 20.0°C. The analyzer 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 tem-
peratures, 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 Pt100 or Pt1000 RTD.
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