EVOM3
World Precision Instruments
33
Issue Possible Cause Solution
Re
si
st
an
ce
reading unusually
low
Cell culture or
media problem
If the cell culture has been given sufficient time to achieve
confluence, and the reading is stable but significantly
lower than expected, then the problem is probably related
to the cell culture. Electrode failure will not generally cause
a lower than expected yet stable reading. Use the test
resistor to verify the meter is functioning correctly. The
meter display should read 1000Ω. See "Instrument
Diagnostics and Calibration" on page 21, "Testing the
STX2-PLUS Electrodes" on page 28 or refer to the ap-
propriate electrode manual for instructions on testing
the electrode. See "APPENDIX E: Improving the Accuracy
and Repeatability of the System" on page 40.
Resistance is a negative value
Contamination on
electrodes
Use the 1000Ω test resistor to verify that the meter is
working correctly. The meter display should show 1000Ω.
See "Instrument Diagnostics and Calibration" on page
21. If a negative value exists only when using the STX
electrode, inspect and test the electrode for the possible
formation of an insulative coating of foreign material that
electrically blocks the current and voltage electrodes.
Remove the foreign material and retest. See "Testing the
STX2-PLUS Electrodes" on page 28 or refer to the ap-
propriate electrode manual for instructions on testing
the electrode. See "Appendix A: KCL Testing Mixtures" on
page 36.
If a red negative value shows on the display only when
using the electrode and the blank setting is off or at
zero, then inspect the electrode for the formation of an
insulative coating of foreign material that electrically blocks
the current and voltage electrodes.
Resistance reading drifts or is
unstable
Electrodes are
not fully im-
mersed in culture
media solution
The meter will not provide a stable reading if the
electrodes are disconnected from the meter or if the
electrodes are not fully immersed into culture media.
Electrodes are
not held still dur-
ing measurement
Handheld electrodes must be kept as motionless as
possible during a measurement. Excessive movement
will cause the measurement to fluctuate.
Charger is
connected to the
meter
The meter reading can become unstable due to the loss
of electrical isolation when the charger is connected to
the AC power. To ensure stability of readings, always
disconnect the charger from the meter when making
measurements.
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