Humidity Sensors and Accuracy Specifications

Humidity Sensors and Accuracy Specifications

When Monnit Humidity sensors are manufactured, they are confirmed to be within the specification listed on the specification sheet. Environmental conditions can affect the accuracy of your sensors. Exposure to things like dust or chemicals can affect the accuracy of Monnit Humidity sensors. Therefore it is important to consider these factors if you find your sensor reporting readings outside of the manufacturer specifications.

The accuracy advertised on the specification sheet is that of the humidity element’s accuracy at the time of manufacturing. This does not guarantee that accuracy over time and is not a replacement for certification.

MoWi WiFi Humidity Sensors

It is worth noting that MoWi WiFi sensors do not offer calibration. Therefore it is possible, especially after some time in use and exposure to environmental factors, the sensor does not provide readings accurate within the specification sheets. If this occurs, you may consider reconditioning the sensors.


If environmental factors (such as temperature, dust, or exposure to chemicals or water) have resulted in an inaccurate reading, it is possible to recondition the humidity sensor. Monnit cautions safety when doing this, and does not take responsibility for accidents that may take place and/or affect the sensor when this is executed. To recondition the sensor:

  • Remove the batteries from the sensor.
  • Bake the sensor at 80°C for 12 hours. This can be done in a standard oven (or similar). Warning: Do not exceed 90°C, this may cause flash memory corruption.

    Doing this will recondition the humidity element and can result in more accurate readings.


When testing the accuracy, it is important to expose (soak) the sensor to a static temperature and humidity for 45 minutes or longer prior to sampling for accuracy. Also, using a reliable reference which reports a consistent static reading in that environment is key. More specifically, the temperature must be accurately aligned with the reference in order to achieve accurate humidity measurements due the temperature dependence of relative humidity.

NIST Certification

Monnit does offer paid NIST Certification for Humidity Sensors. It is important to remember a few details about the certification Monnit offers.

  • Certification is valid for 6 months.
  • The certification certifies that the sensor was tested to be within specification at the time it was tested. While the certificate indicates accuracy, it does not specifically guarantee accuracy for that period of time. As mentioned above, environmental factors can affect sensor accuracy.
  • We test to +/- 5% and +/- 1 C accuracy.

Operating Range

The sensor works stably within recommended Normal Range—see Figure 4. Long-term exposure to conditions outside Normal Range, especially at humidity >80%RH, may temporarily offset the RH signal (+3%RH after 60h). After return into the Normal Range it will slowly return toward calibrated state by itself. Prolonged exposure to extreme conditions may accelerate aging.

Humidity Accuracy Chart
Humidity Accuracy Chart


Current ALTA sensors with firmware 14.x and later offer calibration that is saved to the sensor firmware. This means you can calibrate the sensors in the field to address inaccuracies. When considering Monnit Gen1 and earlier ALTA sensors prior to 14.xx it is important to consider the factors in this article.

MoWi Humidity sensors do not offer calibration, and therefore it is possible the accuracy of these sensors may be affected by environmental factors, and cannot be addressed by calibration.

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