Troubleshooting
Page
70
of
110
Example 1: pH Negative offset – Reading Too Low
Step
Description
Buffer solution
Observed pH
Calibration Data
Conclusion
Step 1
Initial test
7.0
6.5
Not accepted
Offset too big
Step 2
Reducing offset by
mixing buffers
(90% buffer 7.0 +
10% buffer 10) =
buffer 7.3
Before calibration:
6.8
After calibration:
7.0
Accepted.
Red LED will
flash 3 times
Offset reduced.
Reading is 7.0
but real value
should be 6.8
Step 3
Normal calibration
(1 of 3)
7.0
6.7
Before calibration:
7.2
After calibration:
7.0
Accepted.
Red LED will
flash 3 times
Calibration
Success. Offset
Removed
Step 4
Normal calibration
(2 of 3)
4.0
4.0
Accepted.
Red LED will
flash 3 times
Calibration
Success
Step 5
Normal calibration
(3 of 3)
10.0
10.1
Accepted.
Red LED will
flash 3 times
Calibration
Success
Figure 12-2: pH Negative offset - Reading Too Low
Example 2: pH Positive Offset – Reading Too High
Step
Description
Buffer solution
Observed pH
Calibration Data
Conclusion
Step 1
Initial test
7.0
7.5
Not accepted
Offset too big
Step 2
Reducing offset by
mixing buffers
(90% buffer 7.0 +
10% buffer 4) =
buffer 6.7
Before calibration:
7.2
After calibration:
7.0
Accepted.
Red LED will
flash 3 times
Offset reduced.
Reading is 7.0
but real value
should be 7.2
Step 3
Normal calibration
(1 of 3)
7.0
7.3
Before calibration:
6.8
After calibration:
7.0
Accepted
Red LED will
flash 3 times
Calibration
Success
Offset removed
Step 4
Normal calibration
(2 of 3)
4.0
4.0
Accepted
Red LED will
flash 3 times
Calibration
Success
Step 4
Normal calibration
(3 of 3)
10.0
10.0
Accepted
Red LED will
flash 3 times
Calibration
Success
Figure 12-3: pH Positive Offset – Reading Too High
Note:
Use the measurement from the pH sensor when mixing the buffer solutions.
