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Testing a RH5 or RH5X Relative Humidity Sensor

Tools Required:

  • 12V battery
  • Digital voltmeter (DVM)


The RH-5X will run on an excitation voltage from 10 to 36 V DC and will typically draw about 1.2 mA of current.

Current Check:
Connect a 12V battery in series with a current meter to power the RH-5X black (-) and red (+) leads. If the current is higher than 2.5mA, something is wrong and the sensor should be replaced.

Signal Output Check:

  • Power the RH-5X with the 12 V battery connected to the black (-) and red (+) leads.
  • Read the output voltage between the black (-) and signal (clear) leads. The reading must be between 0 and 5 volts. If the reading is greater than 5 volts, there is a problem.
  • Allow sufficient settling time (sometimes several minutes are required) for the reference hygrometer and try to place it's probe as close as possible to the RH-5X.
  • Convert that voltage into a relative humidity (using the formula below) and compare against a reference hygrometer.
  • Relative Humidity = V out x 20
  • If the RH-5X is within 3 percent of the reference, it is good.


  • An output reading of 3.76 Volts is taken across the black and clear leads.
  • Relative Humidity = 3.76 x 20
  • Relative Humidity = 75.2 percent

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