Why Are Cooled Mirror Hygrometers Used as Reference Instruments in Climatic Chambers?

Controlled environmental chambers are used in many test, research and development applications where defined temperature and humidity conditions are required. Chilled mirror hygrometers are used to provide a reference for humidity measurements in the chamber because they use a fundamental measurement technique of humidity and have low drift.

Humidity and temperature probes are built into climatic chambers to provide control feedback for the switching of the condition generation devices (saturator, dryer, heater, refrigerator etc). These probes are usually selected for their response speed, rather than their accuracy. It is frequently important, with regards to many different testing applications, to verify the temperature and humidity conditions of the chamber. This instrument needs to provide the ‘real’ values of the climate inside: it does not always need to respond as quickly as the control probes. It does, however, need to be accurate and repeatable as well as being robust enough to withstand the conditions which are common in climatic testing. For these reasons, an instrument such as a chilled mirror hygrometer are well suited for the application.

Watch how to set up the Michell Optidew 401 in a climatic chamber.

What are the typical applications for humidity measurements in climatic chambers?

One common application for humidity chambers is component failure condition testing. This is where components in the chambers are subjected to a range of conditions to find the extremes of their performance range. Humidity chambers are also used to provide standardized conditions for evaluation of materials, heat exchangers and refrigeration equipment. They are also widely used for tests in the automotive, pharmaceutical, and paper industries.

Humidity chambers vary in size widely: from small chambers for testing electronic components, to large, room-sized, arrangements for testing industrial or transport equipment. They can also come in the form of controlled environment storage vaults for valuable and/or delicate items.

What are the recommended Process Sensing Technologies products?

The Michell Optidew 401 and 501 Chilled Mirror Hygrometer and S8000 Remote Precision Hygrometer work on the proven, fundamental optical dew-point measurement principle, giving unmatched long-term performance. A wide measurement range is available, from the equivalent of <0.5 … 100 %RH at ambient temperatures from -40 … +120 °C.

For easy operation, the Optidew 501 offers both analog and digital communications. Two 0/4-20mA outputs and Modbus RTU over RS485 are standard. An Ethernet connection and SD card for data logging are optional. The instrument can be configured and interrogated locally through the optional touch-screen HMI or operated via a PC using Michell’s software. An adjustable volt-free contact alarm means that Optidew 501 can be used for direct process control.

The S8000 Remote covers an even wider operating range, but with a dew-point accuracy of ±0.1 °C. It also offers a 3rd configurable analogue output and MODBUS RTU communications. A high temperature sensor has been developed to meet the rigorous demands of testing taking place at the extremes of the temperature and humidity envelope. The revised construction of the sensor allows it to provide accurate, repeatable and reliable measurements at temperatures up to 120 °C.