Humidity and Temperature Calibration

Calibration is the comparison of an instrument against a reference. The reference should itself have calibration traceable directly, or in multiple steps, back to an authoritative standard. This is known as measurement traceability.

Calibration improves measurement confidence, enables entities to meet regulatory requirements, enables traceability and provides additional data about the sensor (like drift, repeatability and errors when compared to the reference). It is a vital part of instrument maintenance.

The most common approach is calibrating both the relative humidity and temperature circuits of the device. This is done by using a calibration chamber (like Rotronic's HG2-S) which generates required humidity and temperature conditions. Relative humidity sensors can also be calibrated at ambient temperature and can be achieved by using either saturated or non-saturated salt solutions or humidity validators.

Rotronic's HG2-S and HG2-XL calibration chambers are designed to create the precise humidity and temperature conditions. The chambers are fully sealed, ensuring that any variations in humidity within the chamber are solely due to temperature fluctuations. Humidification is achieved through a water reservoir, while a desiccant system is used for drying. Both the HG2-S and HG2-XL models are equipped with an ISO17025 calibrated control probe, which serves as a reliable calibration reference.

Some of the contributors to the uncertainty budget include reference error, resolution, and thermal gradients. Calibration facilities dedicate significant effort to reducing these uncertainties to enhance accuracy. For in-house calibration departments, the primary source of uncertainty often lies in the reference instrument and the calibration methodology employed.

Accuracy and Precision: The accuracy should align with your requirements, considering the specific applications and standards you need to meet. Range of Measurement: The humidity and temperature range the device can accurately calibrate. Stability: The device should maintain consistent performance without significant drift in readings over the period you intend to use it. Traceability: Ensure that the calibration reference calibration is traceable to national or international standards. Cost: The cost of the device should fit within your budget while meeting your technical requirements.

ISO/IEC 17025 is the principal standard adopted by calibration and testing laboratories. While adherence to ISO 17025 is not compulsory for all facilities, it is obligatory for those who are audited against this standard. If ISO 17025 is not a necessity, we strongly advise following good measurement practices to ensure the integrity of your calibrations.

PST offers a diverse portfolio that includes everything from unsaturated salt solutions and validators to state-of-the-art calibration chambers, as well as advanced chilled mirror hygrometers and dew point generators. Our rich experience and specialized knowledge have fostered strong relationships with leading National Measurement Institutions such as the National Physical Laboratory (NPL) in the UK and the National Institute of Standards and Technology (NIST) in the US.

Expressed as a percentage, relative humidity is the ratio of the water vapor pressure to the saturation vapor pressure of the gas.

In simple terms relative humidity is the ratio of how much water vapor there is in the air compared to how much there could be before condensation occurs.

Calibration systems typically include humidity generators, chilled mirror reference hygrometers, and optional compressors or dryers for low dew-point calibrations.

The test chambers are designed to fit most probes and transmitters and there is the option for customizable probe sleeves.

Yes, all our calibration chambers have the option to program calibration cycles.

Both the HygroGen2 and HygroCal100 Advanced come with a relative humidity probe which doubles as a control element and a reference.

Ideally the reference should be more accurate than the instruments under test, this is where our chilled mirrors come in. All our calibration chambers can be used with a chilled mirror reference.

Yes, our HG2-S calibration chamber is very often used for on-site humidity and temperature calibrations.

Process Sensing Technologies (PST) offers ISO/IEC 17025 accredited calibration services at several locations.

Dew point is the temperature to which you need to cool a gas for condensation to occur.

There is an option for customisable fittings, for large volume calibrations, the transmitter manifolds can be designed specifically for your connection type.

Ideally your dew point transmitters should be calibrated against a chilled mirror which has its own calibration traceable to national standards.

The DCS systems come with a chilled mirror reference as standard.