Friday, July 19, 2024

Humidity Sensor: Basics, Usage, Parameters, and Applications

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Sometimes, after rain, the air feels moist. The water seems to have suspended in the air. However, in certain AC’s you click some buttons and the atmosphere brightens up. How and why does it all happen?

Moisture forms up in the air, resulting in humidity. However, the humidity sensor in your AC picks it up and cleans it up for you. Isn’t that wonderful? Let’s take a look at how it does that.

A humidity sensor (or hygrometer) senses, measures, and reports both moisture and air temperature. The ratio of moisture in the air to the highest amount of moisture at a particular air temperature is called relative humidity. Relative humidity becomes an important factor when looking for comfort.

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Humidity sensors work by detecting changes that alter electrical currents or temperature in the air

Humidity Sensor Types

There are three basic types of humidity sensors:

  • Capacitive
  • Resistive
  • Thermal

All three types of sensors monitor minute changes in the atmosphere in order to calculate the humidity in the air. Let us discuss these types in detail:

1. Capacitive

A capacitive humidity sensor measures relative humidity by placing a thin strip of metal oxide between two electrodes. The metal oxide’s electrical capacity changes with the atmosphere’s relative humidity. Weather, commercial and industries are the major application areas.

The capacitive type sensors are linear and can measure relative humidity from 0% to 100%. The catch here is a complex circuit and regular calibration. However, for designers this a lesser hassle over precise measurement and hence these dominate atmospheric and process measurements.

These are the only types of full-range relative humidity measuring devices down to 0% relative humidity. This low-temperature effect often leads to them being used over wide temperature ranges without active temperature compensation.

2. Resistive

Resistive humidity sensors utilize ions in salts to measure the electrical impedance of atoms. As humidity changes, so do the resistance of the electrodes on either side of the salt medium.

3. Thermal

Two thermal sensors conduct electricity based upon the humidity of the surrounding air. One sensor is encased in dry nitrogen while the other measures ambient air. The difference between the two measures the humidity.

Tips on Humidity Sensor Working

  • Coulometric: An electrolyte is formed by absorption of water resulting in a current level which is proportional to the moisture content in the air.
  • Gravimetric: A drying agent is exposed to moist air, resulting in weight gain by the drying agent. The increased weight corresponds to the amount of moisture.
  • Microwave/Infrared: A transmitted signal varies as the humidity increases. The attenuation is an indication of the moisture content in the medium.

Some Parameters for Judgement

So once you know what it is, and how it works, the next step probably would be to check its working. And how do you do that? By working through some of the below-mentioned parameters.

1. Accuracy

Every sensor has its own calibration curve, based on a 9 point system. It basically pitches the pros against the cons of the particular sensor.

2. Linearity

It indicates the voltage deviation from the BFSL value and the measured output voltage value, converted to relative humidity.

3. Reliability

The measurements often cause the sensor to fall out of sync. However for a sensor to be useful, it has to provide reliable measurements.

4. Repeatability

The measurements from a sensor, have to be so that they don’t drift apart. Repeatability is the measurement of drift among measurements of a single quantity.

5. Response Time

Typically, the time is taken by a sensor to rise to 66% (rise time) or fall to 33% (fall time) of maximum output voltage, is known as the response time.

Applications of Humidity Sensors

The applications of humidity sensor range far and wide. People with illnesses affected by humidity, monitoring and preventive measure in homes employ humidity sensors. A humidity sensor is also found as part of home heating, ventilating and air conditioning systems (HVAC systems). These are also used in offices, cars, humidors, museums, industrial spaces and greenhouses and are also used in meteorology stations to report and predict the weather.

Humidity Sensor-based Projects Ideas

Fridge Temperature and Humidity Indicator

The small sniffer device, described in this project, picks up temperature and humidity from inside the fridge and transmits on an RF link to a nearby receiver unit. The receiver unit checks the received code, identifies the right sniffer device and displays live temperature and humidity.

Why do we need it you say?

We can measure temperature and humidity inside the fridge using a normal temperature-humidity indicator but relative humidity could be inaccurate in that case.

Humidity And Temperature monitoring Using Arduino

In this article, humidity and temperature information from the DHT-11 sensor is analysed graphically on ThingSpeak platform using Arduino MCU and ESP8266 Wi-Fi module.

Humidity Indicator and Controller

Presented here is a simple humidity indicator and controller. In industries such as textile, the change in moisture content has a direct impact on the properties of fabric, such as tensile strength, elasticity, fibre diameter and friction. Therefore the process is executed within a permissible humidity environment only.

Depending on the type of fabric and the process being undertaken, the requirement of particular humidity level varies. Cotton and linen have to be processed at very high relative humidity (RH) levels of around 70-80 percent since they are very brittle. Wool requires RH levels of around 65 percent. Silk needs to be processed between 65 and 70 percent.

With this circuit, you can not only monitor humidity levels between 30 and 90 percent RH but also control it.

IoT-Enabled Air Pollution Meter With Digital Dashboard On Smartphone

Presented here is an IoT enabled air pollution meter to monitor air quality on your smartphone using Blynk application and Arduino board. Blynk is an Internet of Things (IoT) platform to control Arduino, Raspberry Pi and the like over the Internet. In this project Blynk provides a digital dashboard on your smartphone that displays real-time air quality readings for the immediate surroundings.

Humidity Sensor FAQs

What is a humidity sensor?

A humidity sensor is a device that measures the amount of water vapor present in the air or other gases.

How does a humidity sensor work?

There are different types of humidity sensors, but most of them work by measuring changes in electrical resistance, capacitance, or temperature caused by moisture in the air.

What is the accuracy of a humidity sensor?

The accuracy of a humidity sensor varies depending on the type of sensor, the calibration, and the conditions under which it is used. Most commercial sensors have an accuracy of around ±2% relative humidity.

How do you calibrate a humidity sensor?

Humidity sensors can be calibrated using a calibration chamber with a known humidity level or using a salt solution with a known humidity level.

What is the range of a humidity sensor?

The range of a humidity sensor depends on the type of sensor and the manufacturer. Some sensors have a range of 0-100% relative humidity, while others have a more limited range.

How do you maintain a humidity sensor?

Humidity sensors should be kept clean and free of dust and debris. They should also be calibrated regularly to ensure accuracy.

What are some common problems with humidity sensors?

Common problems with humidity sensors include drift, hysteresis, and response time. These issues can be addressed through calibration and proper maintenance.

Can humidity sensors be used in outdoor environments?

Yes, humidity sensors can be used in outdoor environments, but they should be protected from direct sunlight and extreme temperatures. Some sensors are specifically designed for outdoor use.

You can comment on your queries in the comment section given below.

Wanna check out the video on humidity sensor: Working with humidity sensor

Another video showing constructing your own Temperature & Humidity Monitor in Less Than 5 Minutes

A quick guide to humidity sensors in the form of slideshow given below:

Humidity sensor from Nikita Gupta

This article was first published on 9 June 2017 and was recently updated on January 2024.


  1. Hi, can i use a HR202 sensor to replace my SYH-1 sensor in my humidifier?below are the specs for the SYH-1 and the HR202 .
    HR202 specs
    Parameters: (at 1kHz) Unit: OhmOperating range: 20 … 95% RH 0 … 60 ℃
    Supply voltage: 1.5V AC (Max sine wave)
    Operating frequency: 500Hz … 2kHz
    Rated Power 0.2mW: (Max sine wave)
    value: (at25 ℃ 1kHz 1V AC 60% RH sine wave) 31.0kω
    Impedance range: (at25 ℃ 1kHz 1V AC 60% RH sine wave) 19.8 … 50.2kω
    Humidity measuring accuracy: ± 5% RH

    SYH-1 Specs
    Manufacturer SYHITECH
    Sensor type humidity sensor
    Measuring range 20%…95% RH
    Tolerance ±5% RH
    Body dimensions 14 x 18.5 x 5.8mm
    Output configuration analogue voltage
    Operating temperature 0…60°C
    Resistance 23kΩ

  2. Hi,
    I have a quick question regarding the humidity sensor..
    for example, if i will put this sensor in a closet or a bag with wet materials, will it detect the humidity? and after how long?
    Are there any sensors that i can connect to another system like a computer that can send a notification if the humidity goes up?


  3. How large an area can one humidity sensor cover? if I have a 100,000 square foot open space and need to monitor humidity – how many sensors do I need, and do each of them represent like a 10 foot radius or some other limit to their effective representation?

  4. My AC stopped cooling. I think I need Freon. I have an older humidity “sensor” ? that hangs above a newer thermostat or my AC unit. It is rectangular with a round button, and its numbers run from 20 to 80. Does this (Honeywell) relative humidity ? dial, box… have batteries I should be changing?
    I was told by the AC maintenance workers that it should stay all the way down to 20 to keep all the humidity out of the air. Another worker from the same company says that it doesn’t work at all, it’s useless; get rid of it. Another one says that my thermostat should be hooked up to it and wants to replace a new thermostat (This one is not that old and works fine; digital) I change my batteries each year in the thermostat.
    Can someone explain (in layman’s terms; above explanation is way over my head) it’s 93 in my home; outside air is just as hot and I have 5 fans running. Repairs can’t be done till Tuesday. It’s Sunday and really HOT! Thanks in advance . Carol

  5. Hi,
    I tried interfacing Arduino with the humidity sensor. It was showing temperature and is not showing humidity.
    I used this code.

    Serial.print ( ” Temp is ” ) ;
    Serial.print ( temp ) ; // Printing the temperature on display.
    Serial.println ( ” *C ” ) ; // Printing “ *C ” on display.
    Serial.print ( ” Humidity in % is : ” ) ;
    Serial.print ( humidity ) ; // Printing the humidity on display
    Serial.print ( ” % t ” ) ; // Printing “%” on display

  6. I have a broad question about humidity sensors in household temperature/humidity gauges — will they likely become less accurate over time? I bought a ~$30 one for my bedroom, which here in dead of winter has never showed below its 30%-50% “comfort level” indication. I realized I have 5 other temp/humidity devices — two indoor/outdoor weather stations, and two temp/humidity outdoor sensors for one of the weather stations (the other one’s sensor broke long ago and I never replaced it), and a household one that came with an old humidifier. I put them all together in the bedroom and left them overnight, and this morning, the temperatures were all inside a 2-degree range (66-68 degrees F), but the humidity indications varied from 20-36%. But the variation was interesting — the newer the sensor, the higher the humidity it read. In fact the two outdoor sensors (same model, one about 10 years old, the other about a month old) showed a huge variation.


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