ATI
Q45D Portable Dissolved Oxygen
Part 9 - Service
8.5
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.
Dissolved oxygen 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:
3.
Disconnect the five sensor wires from the back of the dissolved oxygen monitor.
Those wires are color coded white, brown, red, black, and green. Note:The
brown wire may be replaced with an orange wire in some cables.
4.
Remove the electrolyte chamber from the sensor and dry the electrodes with a
paper towel.
5.
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.
6.
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.
7. 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 varioustemperatures.
Temperature °C
Resistance
0
1000
5
1019
10
1039
15
1058
20
1078
25
1097
30
1117
35
1136
40
1155
45
1175
50
1194
Figure 12 - Pt100 RTD Table
