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CAP-300 Series Point-Level Troubleshooting Steps


If your Gems CAP-300 Series Capacitive Level Sensor is not performing as expected, please use the steps below to troubleshoot your sensor.

  • Is the power supply correct?  Standard sensors require a 9 to 32 VDC input. 
  • Is the wiring correct?   Wiring schematics can be found in the bulletin (and below), click here


Double check that your wire colors/pinouts match correctly.


Orientation and Mounting:

  • The CAP-300 is designed to work in any orientation 
  • The black plastic tips should be kept at least 0.1” (2.5mm) away from any surface 
  • Is the CAP-300 probe tip fully exposed to the media, and not installed in a port or tube where media can get trapped?   


  • Is the port/tip clean?   
  • Any dried-on debris that could cause a false reading? 


  • The CAP-300 relies on the Dielectric Constant (Dk) of your fluid in order to detect the difference between fluid present and no fluid present. 
  • The sensor switching threshold is factory set at a value of 30.  
  • Media with a Dk greater than 30 will be detected as “WET”. Conversely, media with a Dk less than 30 will be detected as “DRY”.  

Some common Dk values: 

Are you trying to detect foam? The CAP-300 was designed to ignore foam and will not detect it as wet.  

Best Practices for Troubleshooting:

  • Test with room temp tap water.   
  • This way, it is a good known target fluid. 
  • Remove the sensor completely from your mechanical and electrical system.   
  • This will isolate any variable in the circuitry.   
  • Use a known good power supply as well as a known good voltmeter and see if the sensor responds to water. 

If these steps do not yield favorable results, please contact Gems via:   Technical Support