How Do I Know If My Humidity Sensor Is Accurate?

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Alicia Palin

Published on 24 March 2022

GNW explains what humidity sensor calibration involves, how to carry out quick & easy humidity sensor testing yourself, & when to call in the experts.

Humidity sensors are essential to many industrial and domestic applications. From complex weather stations to everyday tumble dryers, humidity sensors are everywhere. But to ensure their peak performance, a regular humidity sensor calibration should be carried out. Here, we explain what humidity calibration involves, how to carry out quick and easy humidity sensor testing yourself, and when to call in the experts to perform a relative humidity calibration.

 

What Is Humidity Calibration?

Humidity calibration involves checking the accuracy of a humidity sensor (hygrometer) and adjusting it for accuracy. A humidity sensor calibration should be performed regularly to ensure they operate within their specifications. Our technicians at GNW Instrumentation calibrate a huge variety of humidity meters, including probes, transmitters, relative humidity meters, psychrometers, thermohygrographs, and digital indicators.

 

How Do Humidity Sensors Work?

Humidity sensors detect minute atmospheric changes that can alter electrical currents and the temperature in the air. Relative humidity is the amount of water vapour in air expressed as a percentage of the amount needed for saturation at the same temperature. Precise temperature readings are therefore vital for achieving an accurately calibrated temperature and humidity monitor.

 

There are three main types of humidity sensors:

  • Capacitive
  • Resistive
  • Thermal

 

Capacitive

Capacitive humidity sensors measure relative humidity using a thin strip of metal oxide between two electrodes. As the atmosphere’s relative humidity changes, so does the metal oxide’s electrical capacity. Capacitive humidity sensors are typically used in heating, ventilation, and air conditioning (HVAC) systems and weather stations.

 

Resistive

Resistive humidity sensors employ ions in salts to measure the electrical impedance of atoms. Any changes in humidity will directly affect the resistance of the electrodes on either side of the salt. Due to their low cost and relatively small size, resistive sensors are used in a wide range of residential, industrial and domestic applications.

 

Thermal

Two thermal sensors conduct electricity due to the humidity in the surrounding air. One sensor measures ambient air, while the other is hermetically sealed in dry nitrogen. The difference between the two indicates the humidity level. Thermal sensors are used in a variety of applications, including tumble dryers and drying kilns.

 

Why is it important to measure humidity? 

Measuring humidity is important in manufacturing and laboratory settings to prevent a range of issues, including condensation, mould and corrosion. An accurate humidity sensor can eliminate the spoilage of products, saving time and money. Precise temperature readings are essential for achieving accurate relative humidity measurements. A temperature variance of just 1°C, can impact a humidity measurement by as much as 3-4%.

 

What is the humidity sensor calibration salt procedure?

Here at GNW, we test humidity sensors using humidity calibration salts. This standard humidity calibration procedure, which uses specific salts to create micro-environments of known relative humidity percentages, involves the following steps:

 

  • Step 1 – We dissolve the salts in an aqueous solution within a sealed container.
  • Step 2 – We take multiple readings from the sensor that we are testing. 
  • Step 3 – We then compare the obtained values with the reference standard.
  • Step 4 – We repeat this humidity calibration process using several different salts. 
  • Step 5 – We begin to form a detailed profile for the humidity meter being tested. 
  • Step 6 – We analyse the degree of deviation from the specified relative humidity. 
  • Step 7 – We now have a clear understanding of the relative humidity meter’s accuracy.

 

How To Check A Humidity Sensor

You can perform your own makeshift relative humidity calibration using table salt to check if your humidity sensor needs calibrating professionally. You will need a zip lock bag, a bottle cap, table salt and some distilled water. 

 

  • Fill the bottle top with salt and enough water to form a slurry but not enough to dissolve the salt.
  • Carefully place the bottle top and your humidity sensor into the zip lock bag and seal it.
  • Put this aside for six hours for the humidity sensor to record the humidity inside the bag.
  • The known relative humidity for table salt mixed with distilled water is 75% at room temperature (20°C).
  • The amount of deviation from this figure will tell you whether your humidity sensor requires calibrating or not.  

 

Humidity Sensor Calibration Experts

A calibrated humidity meter can mean the difference between efficient manufacturing processes and costly spoilage of products. A professionally executed humidity sensor calibration can save you time, money and operational headaches, and GNW Instrumentation can take care of all your humidity calibration needs.

 

We understand that time is money, which is why we aim to deliver fast, precise and efficient moisture humidity sensor calibrations. You can expect same-day results from an on-site calibration or a turnaround of just a couple of days with our off-site service. For 10 or more items, we will collect and return your instruments for free. Get your free, no-obligation quote today and if you find a calibration service cheaper elsewhere we will beat the price! 

 

GNW provides high-quality calibration services and supplies all types of instrumentation and measuring equipment to a range of industries worldwide. For over 40 years, we have built an excellent reputation for quality production and repair of pressure gauges, calibration equipment, weighing equipment, temperature sensors, and more. 

 

At GNW, we offer a range of quality services that ensure accurate results. Our on and off-site calibration and certification is designed to help you achieve complete accuracy from your instrumentation, and our other services, such as repairs and manufacture of custom instrumentation, are equally as important to us and our customers. 

 

For more information, or to speak to one of our technical experts, please contact us on +44 (01704) 536 010 or info@gnw.co.uk