ATI
Q46H/79PR Chlorine Manual
Part
10 – Troubleshooting
68
O&M Manual
Rev-E (5/17)
If you suspect that water has gotten into a cable connection on a flow type sensor or into
the plug connection of a submersible sensor, disconnect the cable and allow the parts of
the sensor to sit in a warm place for 24 hours. If water in the connector is the problem, it
should dry out sufficiently to allow normal sensor operation. However, steps 2c thru 2e
above will have to be repeated after drying to see if the problem is gone.
3. Acid clean the measuring electrode in accordance with the procedure in section 9.4 Sensor
Acid Cleaning.
10.6 Troubleshooting (Q22P Sensor)
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 9
should always be the first step in any troubleshooting.
If the sensor cannot be calibrated after cleaning, replace the saltbridge and reference cell buffer
pH 7 as outlined in Section 9.
If the sensor still cannot be calibrated, perform the following test. A multimeter, pH 7 buffer and
pH 4 buffer 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 black and red 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.
Connect the multimeter’s positive (+) lead to the red wire and its negative (-) lead to the black
wire. With the sensor in the pH 7 buffer at approximately 20-30 ºC, measure the DC
millivolts. The sensor reading should be between 680 – 750 mV. If it is not, replace sensor
reference solution, saltbridge and re-test.
5.
With the multimeter connected as in Step 4, rinse the sensor with clean water and place it in
the pH 4 buffer. Allow the temperatures to equilibrate as before. Now measure the sensor
span reading. It should be b450 – 550 mV.
