Hach-Lange pHD sc - Manual (Page 31)

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Troubleshooting
Span Reading in pH 10 Buffer
With the sensor in pH 10 buffer, the sensor span reading should be at least –160 mV less
than the noted offset reading taken in step 5.
If the span reading is at least +160 mV more than or – 160 mV less than the offset reading
in pH 4 or pH 10, respectively, the sensor is within factory-specified limits. If not, contact
Technical Support.
6.3.2 Troubleshooting the pH Sensor with Integral Digital Electronics
1. Place the sensor in pH 7 buffer and allow the buffer and sensor to reach temperature
equilibrium. This can be verified by monitoring the sensor temperature value for a
stable temperature measurement. This value is shown on the sc controller display
when it is in measurement mode.
2. From the Sensor Setup Menu on the sc controller, select “Diag/Test” and confirm.
3. Select “Sensor Signal” and confirm. This sensor offset reading should be within
factory-specified limits of –50 and +50 mV. If it is, write down this millivolt value
reading and perform step 4. If the reading is outside these limits, discontinue this test
and contact Technical Support.
4. Rinse the sensor and place it in pH 4 or 10 buffer and allow the buffer and sensor to
reach temperature equilibrium. This can be verified by monitoring the sensor
temperature value for a stable temperature measurement. This value is located on the
sc100 display when it is in measurement mode.
5. From the Sensor Setup Menu on the sc controller, select “Diag/Test” and confirm.
6. Select “Sensor Signal” and confirm. Then measure the sensor span value.
Span Reading in pH 4 Buffer
With the sensor in pH 4 buffer, the sensor span reading should be at least +160 mV more
than the offset reading as shown in
Table 8 and Table 9 .
Table 7 Typical Span Reading Examples (pH 10 buffer)
Offset Reading
(in pH 7 buffer)
Span Reading (in pH 10 buffer)
–50 mV –210 mV
–25 mV –185 mV
0 mV –160 mV
+25 mV –135 mV
+50 mV –110 mV
Table 8 Typical Span Reading Examples (pH 4 buffer)
Offset Reading (in pH 7 buffer) Span Reading (in pH 4 buffer)
–50 mV +110 mV
–25 mV +135 mV
0 mV +160 mV
+25 mV +185 mV
+50 mV +210 mV