FAQ: Troubleshooting Unstable Resistance Readings from an ENDOHM

ENDOHMOne of our frequently asked questions (FAQs) concerns TEER measurements with an EndOhm. If the resistance readings from your ENDOHM don't stabilize, you may need to do some troubleshooting.

Test the EVOM2

First, test your EVOM2 meter. The 1000Ω test resistor (WPI # 91750) can be used for this purpose.

This test resister fits into the RJ-11 plug on the EVOM2

  1. Insert the RJ-11 plug at the end of the test resistor  into the Input port on the meter.
  2. Set the Function Switch to Ohms.
  3. Disconnect the EVOM2 from the charger and turn the Power on (I). The meter should display 1000Ω. If not, adjust the R ADJ screw with a small slot-head screwdriver until the meter shows a reading of 1000Ω. If the EVOM2 reads 1000 ± 2-3 ohms, and the reading remains stable, then the EVOM2 is working correctly.

See the related video.

Test the ENDOHM

Next, test the ENDOHM. You can still test the ENDOHM qualitatively by exposing it to different KCl concentrations. The readings should always be a stable, lower TEER value at higher concentrations, and a higher but potentially less stable value at lower concentrations.

In general, if the TEER reading is falling, it means that the current is finding an alternative path of lower resistance than through the media alone, or the preparation is somehow adopting a charge. If the problem is truly in the ENDOHM, it will typically be caused by a leak of culture media beneath the electrode surfaces, where it can attack wire bonds to the Ag/AgCl disks. A delayed reaction may take time for the media to creep into very fine fissures where the glue bond has lost seal integrity. If the TEER reading continually drifts downward well below the expected value, then the ENDOHM most likely has a leak at the electrode bond or corrosion somewhere in the current or voltage pathways.

If the ENDOHM has developed fine fissures, it needs to be replaced.

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