ATI
Q45P pH System
Part 7
–Troubleshooting
43
O&M Manual
Rev-B (7/15)
7.3 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 3.1 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 3.2.
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 mu
ltimeter’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:
ºC
RTD
Ω
20
1078
25
1097
30
1117
35
1136
