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I'm doing a project on humidity monitoring using HR202 Humidity sensor and PIC16F877A.I could not find resolution & accuracy of HR202 in online.So please help me to calibrate and use HR202 humidity sensor(not module).

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    \$\begingroup\$ I dunno what you're doing wrong. I Googled HR202 Humidity and the second item I got back was www.elecrow.com/download/HR202%20Humidity%20Sensor.pdf \$\endgroup\$ Oct 11 '15 at 4:58
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As WhatRoughBeast already mentioned the data sheet is readily available by simply goolgling "HR202 Humidity". Here is the link. The accuracy and resolution are clearly stated.

Note that the sensor is analogue and requires an AC voltage! It is not a particularly user friendly Humidity sensor for this reason. It is a resistor which changes its resistance based on the humidity of the environment. How accurate your final humidity reading will be will also be a function of how accurately you can measure its resistance.

On the datasheet there is a table which tabulates the resistance of the sensor at various Relative Humidity levels given a certain temperature. From this you can create a 2 parameter equation in software which takes the current temperature, and resistance value from the sensor as inputs and calculates your humidity value. Note, you will also need a temperature sensor to use this humidity sensor accurately.

Actually Calibrating a Humidity Sensor: Humidity Sensors are notoriously difficult to calibrate, because you need a known Relative Humidity value to calibrate against. The way this is usually done is using saturated salt solutions, which at equilibrium result in known relative humidities. Here is a paper tabulating the produced relative timidities at different temperatures: http://nvlpubs.nist.gov/nistpubs/jres/81A/jresv81An1p89_A1b.pdf

From these values you can calibrate your sensor if need be.

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  • \$\begingroup\$ Sir How do I know resistance sir.The HR202 sensor outputs a voltage according to RH.I have added a temperature sensor.also How to create an equation which give me correct RH output? Please help me to learn Sir ... \$\endgroup\$ Oct 12 '15 at 2:55
  • \$\begingroup\$ That's the problem - the HR202 does NOT output a voltage according to RH. Rather it changes its AC resistance. Honestly, my recommendation would be find a different humidity sensor. This sensor doesn't do what you think it does and is not easy to use with a micro-controller such as the PIC. Look for DC humidity sensors from Honeywell or Sensirion (more expensive), or cheaper look at the DHT22. \$\endgroup\$
    – Rohan
    Oct 12 '15 at 14:23

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