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MODEL SOLU COMP II SECTION 8.0
TROUBLESHOOTING
8.6 SIMULATING INPUTS — pH
8.6.1 General
This section describes how to simulate a pH input into the Solu Comp analyzer. To simulate a pH measurement,
connect a standard millivolt source to the transmitter. If the transmitter is working properly, it will accurately meas-
ure the input voltage and convert it to pH. Although the general procedure is the same, the wiring details depend
on the location of the preamplifier.
8.6.2 Simulating pH input when the preamplifier is in the analyzer.
1. Turn off automatic temperature correction and solution tempera-
ture correction. From the Program menu, choose Temp. Then
choose Live/Manual and enter 25°C. See Section 5.6 for details.
2. Disconnect the sensor and connect a jumper wire between termi-
nals 1 and 6 and terminals 4 and 6 on TB4. See Figure 8-2.
3. From the display menu choose the pH/temperature/mV screen.
The measured voltage should be 0 mV and the pH should be
7.00. Because calibration data stored in the analyzer may be off-
setting 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 terminals 1 and 6 and connect the voltage source
as shown in Figure 8-2. Be sure to jumper the reference and solution ground terminals.
5. Calibrate the analyzer using the procedure in Section 6.3. 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 properly it should accept the calibration. The slope should
be 59.16 mV/pH and the offset should be zero.
6. To check linearity, return to the main display and the pH/temperature/mV screen. 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.
8.6.3 Simulating pH input when the preamplifier is in a
junction box.
The procedure is the same as described in Section 8.6.2.
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 as shown in
Figure 8-3.
8.6.4 Simulating pH input when the preamplifier is in the sensor.
The preamplifier in the sensor simply converts the high impedance signal into a low impedance signal without
amplifying it. To simulate pH values, follow the procedure in Section 8.6.2.
FIGURE 8-2. Simulating Inputs When
the Preamplifier is in the Analyzer
Voltage (mV) pH (at 25°)
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 8-3. Simulating pH Input When the
Preamplifier is in the Sensor.