ATI
Q46H/65 Residual Chlorine Dioxide System
Part 10
– Troubleshooting
65
O&M Manual
Rev-J (11/18)
10.5 Sensor Tests
1. Check the membrane condition. A membrane that is not stretched smoothly across the tip of
the sensor will cause unstable measurements. If necessary, change membrane and
electrolyte.
2. Chlorine dioxide sensors can be tested with a digital voltmeter (DVM) to determine if a major
sensor problem exists. Follow the steps below to verify sensor integrity:
A. Disconnect the five sensor wires from the back of the ClO
2
monitor. Those wires are
color coded white, brown, red, black, and green. Note that the brown wire may be
replaced with an orange wire in some cables.
B. Remove the electrolyte chamber from the sensor and dry the electrodes with a paper
towel.
C. Connect a DVM between the white and brown (or orange) wires. Reading resistance,
you should find an open circuit value of infinite resistance. There must be no measurable
resistance at all between these wires. Any resistance at all indicates either water in the
cable connector or the breakdown in an electrode seal.
D. Connect a DVM between the red and white wires. The red wire is part of the RTD circuit
and the white wire is part of the measuring cell. There should be no connection. Reading
resistance, you should find an open circuit value of infinite resistance. Any resistance at
all indicates either water in the cable connector or the breakdown in an electrode seal.
E. Connect the DVM between the red and black wires. These are the RTD leads, and you
should find a resistance value that depends on the temperature. The table below lists the
resistance values for various temperatures. Reading resistance between the red and
green wires should give exactly the same values as between red and black.
Temperature °C
Resistance
0
100.0
5
101.9
10
103.9
15
105.8
20
107.8
25
109.7
30
111.7
35
113.6
40
115.5
45
117.5
50
119.4
Figure 31 - Pt100 RTD Table
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 2cthru 2e
above will have to be repeated after drying to see if the problem is gone.
