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MODEL 54eA SECTION 15.0
TROUBLESHOOTING
15.13 SIMULATING INPUTS - pH
15.13.1 General
This section describes how to simulate a pH input into the controller. To simulate a pH measurement, connect a
standard millivolt source to the controller. If the controller is working properly, it will accurately measure the input
voltage and convert it to pH. Although the general procedure is the same, the wiring details depend on whether the
preamplifier is in the sensor, a junction box, or the controller.
15.13.2 Simulating pH input when the preamplifier is in the analyzer.
1. Turn off automatic temperature correction (Section 5.9) and solution temperature correction (Section 5.8, step
8). Set the manual temperature to 25°C.
2. Disconnect the sensor, including the jumper between the ANODE and REFERENCE IN terminals, and con-
nect a jumper wire between the pH IN and the REFERENCE IN terminals.
3. From the Diagnostics menu scroll down until the "pH input" line is showing. The pH input is the raw voltage
signal in mV. The measured voltage should be 0 mV and the pH should be 7.00. Because calibration data
stored in the analyzer may be offsetting the input voltage, the displayed pH may not be exactly 7.00.
4. If a standard millivolt source is available, disconnect
the jumper wire between the pH IN and the REFER-
ENCE IN terminals and connect the voltage source as
shown if Figure 15-3.
5. Calibrate the controller using the procedure in Section
11.0. Use 0.0 mV for Buffer 1 (pH 7.00) and -177.4 mV
for Buffer 2 (pH 10.00). If the analyzer is working prop-
erly, it should accept the calibration. The slope should
be 59.16 mV/pH and the offset should be zero.
6. To check linearity, set the voltage source to the values
shown in the table and verify that the pH and millivolt
readings match the values in the table.
15.13.3 Simulating pH input when the preamplifier is in a junction box.
The procedure is the same as described in Section 15.11.2. 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 15-3.
15.13.4 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 15.13.2.
Voltage (mV) pH (at 25°C)
295.8 2.00
177.5 4.00
59.2 6.00
-59.2 8.00
-177.5 10.00
-295.8 12.00
FIGURE 15-3. Simulate pH