WPI EVOM, Instruction Manual

EVOM

TROUBLESHOOTING

EVOM Meter

Experience demonstrates that more than 90% of the time, system problems are related 
to the electrode not the meter itself. Of those failures due to the meter itself, at least half 
of them are a result of a failed switch due to the presence of corrosion. The typical cause 
of this corrosion is accidental spillage of saline solution or culture media on the meter. 
If the meter has been kept free of salt solutions, the batteries are fresh and functional 
testing of the meter demonstrates acceptable performance results (see the INSTRUMENT 
SELF-TEST section of this manual), then the meter is working correctly. 

STX2 Electrode

•  Although the 

STX2 

electrode has a warranty of 30 days, its useful lifetime is typically 

1 to 2 years, depending on usage. 

•  When the electrodes fail, the most common symptom is an unstable or unusually 

high reading. If the current electrode fails, the meter will emit a warning beep. 

•  When the meter displays a lower than expected resistance, but is stable and 

reproducible, the most likely cause is related to the cell culture, not the electrode or 
meter.

• 

In situ

 tests — There is no quantitative method available to do an 

in situ

 or wet test on 

the electrode. However, two qualitative methods may assist the user in determining 
that the electrode is working and will respond to an increase in resistance: 

1. 

Use WPI’s 

CaliCell 

to test the electrode.

CaliCell 

is a cell culture insert with a 

synthetic membrane that mimics a confluent epithelial membrane’s resistance in 
fluid. Each 

CaliCell 

insert is supplied with an established resistance measurement 

determined at the time of manufacture and against which the system resistance 
can be compared.

2. 

Test the resistance differences between a well filled with electrolyte and a blank 
culture insert filled with electrolyte. The resistance of electrolyte alone should be 
less than 50 ohm and stable, if the electrode is kept stationary. The resistance of 
the blank insert is normally in the 80 to 200 

Ω

 range, depending on the brand 

and size. 

NOTE:

 During normal usage, it is helpful to write down the resistance range of each 

particular type of blank insert with the specific culture media used. If the electrode is 
subsequently suspected of having a problem, a comparison of current readings to past 
readings on the same blank insert and culture media could assist in determining if the 
electrode is functioning as expected. 

WORLD PRECISION INSTRUMENTS                                                                                                                                  15