WPI EVOM3 - Page 36

32 World Precision Instruments
Issue
Possible Cause Solution
Resistance is a negative value
Contamination on
electrodes
U e the Ω tet eit t ei that the mete i
ing etl he mete dila hld h Ω
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 35.
If a red negative value shows on the display only when
ing the eletde and the lan etting i   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
ill ae the meaement t tate
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.
Resistance reading
drifts or is unstable
Old electrode Use the test resistor to verify the meter is functioning
correctly. The meter display should read 1000 Ω. See
"Instrument Diagnostics and Calibration" on page 21
or "Testing the STX2-PLUS Electrodes" on page 28.
The lifetime of the electrodes is between 1- 2 years with
normal use. See the previous note on corrosion and the
note on coatings. See "Appendix A: KCL Testing Mix-
tures" on page 35.