ATI
Q45P pH System
Part 7
–Troubleshooting
44
O&M Manual
Rev-B (7/15)
5. Reconnect the yellow and white wires.
6.
Connect the multimeter’s positive (+) lead to the red wire and its negative (-)
lead to the green wire. With the sensor in the pH 7 buffer at approximately
20-30 ºC, measure the DC millivolts. The sensor offset reading should be
between
–50 and +50 mV. If it is not, replace sensor reference solution and
saltbridge (See Section 3.2) and re-test.
7. With the multimeter connected as in Step 5, rinse the sensor with clean water
and place it in the second buffer. Allow the temperatures to equilibrate as
before. Now measure the sensor span reading. Use the following table to
determine approximate mV:
pH
mV
2.00
+296
4.00
+178
7.00
0
9.18
-129
10.00
-178
NOTE:
The mV values listed above are for ideal conditions (sensor
offset = 0 mV) and therefore represent midpoints in a range.
The table shows the difference in mV which should be seen
when going from one pH value to another. For example, at
7.00 pH, the mV reading will be from
–50 to +50 mV (at room
temperature) if the sensor is working properly. If the reading
is e20 mV, then going to 4.00 pH buffer should produce
a reading of +198 mV, or a difference of +178 mV.
