MODEL 54eA | SECTION 16.0 |
| TROUBLESHOOTING |
16.13 SIMULATING INPUTS - pH
16.13.1 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.
16.13.2 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 connect 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
5.Calibrate the controller using the procedure in Section 11.0. Use 0.0 mV for Buffer 1 (pH 7.00) and
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.
| Voltage (mV) | pH (at 25°C) |
|
| 295.8 | 2.00 |
|
177.5 | 4.00 |
| |
| 59.2 | 6.00 |
|
| 8.00 |
| |
10.00 |
| ||
12.00 |
| ||
|
|
|
|
FIGURE 16-3. Simulate pH
16.13.3 Simulating pH input when the preamplifier is in a junction box.
The procedure is the same as described in Section 16.11.2. 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
16.13.4 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 16.13.2.