WPI EVOM - Page 41

EVOM™ Manual
World Precision Instruments 37
Issue
Possible Cause Solution
Voltage reading is unstable
Electrodes are
heavily charged
or dirty
Clean the electrodes as per the instruction manual for
the electrode.
Electrode too
close to strong
electromagnetic
radiation device
Move the system to a dierent area away from sources
of electromagnetic elds. Electromagnetic eld sources
could include computers, MRI equipment, magnetic
stirrers, etc. Cell phone signals can also interfere.
Power line or USB
connected to a
recording device
causing noise
Remove the USB connection to eliminate the possibility
of a ground loop.
Voltage reading is can not be set near zero
Electrode not
equilibrated
The Ag/AgCl electrodes (inner voltage measurement
electrodes) on the probe may become polarized due to
an uneven distribution of ions between the electrode
pair. This ionic charge can be neutralized by immersing
the probe into 0.1M KCL for 24 hours with the probe
electrodes shorted electrically. The probe is shorted
electrically when it is connected to the meter with the
power OFF, and the FUNCTION switch in the OHMS
position. See "Probe Null" on page 15 for information
on how to null the electrodes.
Electrode
requires cleaning
Clean the electrode as per the instructions manual for
the electrode.
Contamination
between
electrodes
Inspect the inter-electrode surface areas for material
which could form an insulative coating on the surface
of the inner and outer electrodes. If the material cannot
be removed, the electrode should be replaced.
Corrosion has
formed on
conductive traces
An insulative, transparent coating protects the copper
conductors that connect each electrode to the main
wiring in the handle. When the probe is very old, this
coating can deteriorate, allowing the salts in the media
solution to leech through to the copper conductors.
This is observed as a black discoloration on the copper
circuit traces underneath the conformal coating. If this
is observed, replace the electrode.
Resistance
reading
unusually high
Contaminated
electrode
contacts
With use, the chopstick electrode probe contacts may
acquire a buildup of protein or other foreign material
that eectively increases the baseline resistance of the
electrodes. The electrodes can be cleaned using various
methods.