Calibration and testing of humidity in temperature and humidity sensors - News - Global IC Trade Starts Here Free

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When it comes to calibrating and testing humidity in a temperature and humidity sensor, there are two primary approaches: using a humidity reference or comparing the sensor to a known accurate instrument. A humidity reference can be created using substances like thionyl chloride or potassium hydride solutions, or through saturated salt solutions. When setting up such references, it's crucial to ensure that the container used is well-sealed and that the temperature remains stable. The system must also be allowed enough time to reach equilibrium, which can sometimes take a long time. However, introducing an air pump to circulate air through the solution can significantly speed up the process.

Regardless of the method chosen, it’s always beneficial to have a separate way of measuring the reference humidity. This secondary method, while not highly precise on its own, helps identify when equilibrium has been reached, reducing the risk of major errors. One key limitation of using these types of humidity references is that they may not be suitable for all sensors, especially those that alter their local environment by absorbing or releasing moisture—such as dew point meters or wet and dry thermometers—or those that introduce temperature gradients, like chloride buttons. For accurate results, a proper airflow is essential during the calibration process.

The most reliable way to calibrate any sensor is to compare it with a known good instrument under real-world humidity conditions. In summer, relative humidity between 50% and 90% is often found between noon and midnight. Alternatively, a continuous water spray in a bathroom can create high humidity levels, while a central heating system can produce lower humidity (around 50% or less) indoors. At 20°C, room humidity is typically around 60%, but raising the temperature to 32°C can drop it to about 30%. The best instruments for use as humidity references include wet and dry thermometers and dew point meters. Dew point meters, in particular, offer high accuracy due to their precisely calibrated thermometers, though they tend to be more expensive.

The Asman ventilated wet and dry thermometer is considered ideal for most applications, and even a standard rotary wet and dry meter is usually accurate enough for general use. Many professionals rely on a simple rotary wet and dry meter as a baseline for calibrating more specialized equipment. By using this approach, you can ensure consistency and reliability in your measurements without overcomplicating the process.