WPI EVOM - Page 42

38 World Precision Instruments
Issue
Possible Cause Solution
Resistance reading
unusually low
Cell culture or
media problem
If the cell culture has been given sucient time to achieve
conuence, and the reading is stable but signicantly
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. Refer to the appro-
priate electrode manual for instructions on testing the
electrode. See "Appendix C: Improving the Accuracy and
Repeatability of the System" on page 45.
Resistance reading drifts or is unstable
Electrodes
are not fully
immersed 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 during
measurement
Handheld electrodes must be kept as motionless as
possible during a measurement. Excessive movement
will cause the measurement to uctuate.
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.
Old electrode Use the test resistor to verify the meter is functioning
correctly. The meter display should read 1000 Ω. The
lifetime of the electrodes is between 1- 2 years with
normal use. See the previous note on corrosion and the
note on coatings.
Resistance is a negative value
Contamination on
electrodes
U se the 1000Ω test resistor to verify that the meter is
working correctly. The meter display should show 1000Ω.
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. Refer to the appropriate
electrode manual for instructions on testing the
electrode.
If a red negative value shows on the display only when
using the electrode and the blank setting is o 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.