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MODEL 3081 pH/ORP SECTION 12.0
TROUBLESHOOTING
12.8.2 pH Simulation When the Preamplifier Is Located in the
Transmitter.
1. Verify that switch S-1 is set to "transmitter". See Section 2.2.
2. Turn off sensor diagnostics. See Section 8.4.
3. Turn off automatic temperature compensation. Set manual temperature
compensation to 25°C. See Section 8.5.
4. Disconnect the sensor and wire the transmitter as shown in
Figure 12-7.
5. Attach a jumper between TB-7 (REF IN) and TB-10 (pH IN).
6. Measure the voltage. Press DIAG on the IRC. The InPut voltage in
millivolts will appear in the temperature-output area. The main display
will continue to show pH. The measured voltage should be 0 mV, and
the pH should be approximately 7. Because the calibration data in the
transmitter may be offsetting the input voltage, the displayed pH may
not be exactly 7.0. If the actual readings are close to expected, the
transmitter is probably operating properly.
7. If a standard millivolt source is available, remove the jumper between
TB-7 and TB-10 and connect the voltage source.
8. Following the procedure in Section 7.5, calibrate the transmitter. Use
0.0 mV for pH 7 (bF1) and -177.4 mV for pH 10 (bF2). If the transmitter
is working, it should accept the calibration.
9. To check linearity, leave autocalibration and return to the main display.
Set the voltage source to the values in the table and verify that the pH
reading matches the expected value.
12.8.3 pH Simulation When the Preamplifier Is Located in a Remote Junction Box or in a Sensor-Mounted
Junction Box.
1. Verify that switch S-1 is set to "sensor or junction box". See Section 2.2.
2. Turn off sensor diagnostics. See Section 8.4.
3. Turn off automatic temperature compensation. Set manual temperature compensation to 25°C. See Section 8.5.
4. Disconnect the sensor and wire the sensor side of the junction box as shown in Figure 12-8. Leave the inter-
connecting cable between the junction box and transmitter in place.
FIGURE 12-8. pH Simulation When the Preamplifier Is Located in a Remote
Junction Box or in a Sensor-Mounted Junction Box.
Voltage (mV) pH
295.8 2.00
118.3 5.00
-118.3 9.00
-295.8 12.00
FIGURE 12-7. pH Simulation When the
Preamplifier Is Located in the Transmitter.
5. Attach a jumper between TB1-7
(REF IN) and TB1-10 (pH IN).
6. From this point on, continue with
steps 6 through 9 in Section 12.8.2.
For testing using a standard millivolt
source, be sure to remove the
jumper between TB1-7 and TB1-10
before connecting the standard mil-
livolt source.