ATI
Q46P pH System
Part 8 – Maintenance and Troubleshooting
69
O&M Manual
Rev-F (8/17)
Figure 36 - Replacing the Saltbridge and Reference Buffer
8.6 Troubleshooting
The first step in resolving any measurement problem is to determine whether the trouble lies in
the sensor or the transmitter. Since measurement problems can often be traced to dirty sensor
electrode glass and/or saltbridge, cleaning the sensor using the method outlined in Section 8.4
should always be the first step in any troubleshooting.
If the sensor cannot be calibrated after cleaning, replace the saltbridge and reference cell buffer 7
pH as outlined in Section 8.5.
If the sensor still cannot be calibrated, perform the following test. A multimeter, 7 pH buffer and
another buffer at least 2 pH units away will be needed.
1.
With transmitter power on and sensor connected, place the multimeter’s positive (+) lead on
the white position of the transmitter terminal strip and the negative (-) lead on the black
position. The multimeter should read between –4.2 and –6.5 VDC.
2.
Disconnect the sensor’s red, green, yellow, and white wires from the transmitter or junction
box. Re-check Step 1.
3.
Place the sensor in pH 7 buffer. As in calibration, allow the temperatures of the sensor and
buffer to equilibrate at room temperature (approximately 25 ºC).
4.
Verify that the sensor’s temperature element (Pt1000 RTD) is functioning properly by
measuring the resistance between the sensor’s yellow and black wires. The nominal
resistance value at 25 ºC is 1097 ohms. Use the following table as a guide to the
approximate resistance value: