Water Monitoring System
User Manual
Page
70
of 82
Ver. 1.1 – Revision March 2022
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 large
Step 2
Reduce 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 10.1: 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 large
Step 2
Reduce 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 10.2: pH positive offset – reading too high
Note:
Use the measurement from the pH sensor when mixing the buffer solutions.
