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109118-1 Rev. A, 10/96
3.4 Problem Solving (cont)
3.4.2 Meter Error Codes (cont)
Slope is a value that compares the actual slope determined by
the calibration to the theoretical slope defined by the Nernst
equation. This value is displayed as a percent of theoretical and
is called electrode efficiency (see Section 3.1 for Basic Theory).
Generally the slope value can be interpreted as follows:
95 - 105% Everything is probably working fine.
90 - 95% Electrode needs maintenance. Fresh fill solution
and general cleaning.
85 - 90% Stop and do full electrode maintenance now.
Below 85% Will not calibrate. Do full electrode maintenance
or replace the electrode.
Refer to the electrode manufacturer’s instructions for full details
on maintenance, cleaning and reconditioning electrodes.
Although slope is useful in generally determining when it is time
to do maintenance on an electrode, response time is, by far, the
critical factor effecting accuracy of measurements. When moving
from the 7.00 to the 4.00 buffer during calibration you should
have a stable value in 10-20 seconds. Give a 7.00 to 10.01
calibration 20-30 seconds for a stable value. If it takes longer, the
electrode response is getting slow and the calibration may not be
accurate. Refer to the manufacturer's instructions for electrode
maintenance.
3.4.3 Electrode Problem Solving
Slow response or unstable readings in calibration buffers is
usually related to the condition of the reference fill solution or its
flow through the junction.
1. The fill solution acts as an electrical conductor between the
reference inside the electrode and the solution under test.
Empty the electrode and refill with fresh fill solution
regularly.
3
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