Vaisala offers a range of measurement devices to measure relative humidity levels in various environmental conditions in test chambers.
Virtually every substance and material is sensitive to relative humidity (RH) and temperature in some way.
Consequently, it is necessary to create spaces or test chambers where RH and temperature can be carefully controlled for the purpose of determining exactly how changing environmental conditions may affect the objects of interest.
Selecting RH measurement devices for use in chambers requires careful evaluation. Vaisala’s range of RH measurement devices offers unique solutions for:
- Continuous high humidity
- Aggressive gases
- Extremely dry environment
- Verifying high RH
- Pressure, RH and temperature
- OEM solutions for test and calibration
Vaisala’s test and measurement solutions are easy to install and have low maintenance requirements.
Featuring proven and reliable designs, these RH measurement devices can be customised to suit specific testing requirements.
Continuous high humidity
Environments that run at or near saturation are difficult for most electrical humidity sensors.
Vaisala has created ‘warmed probe’ instruments specifically for high RH measurements.
Warmed probes are automatically kept at a temperature several degrees higher than the surrounding temperature.
This prevents condensation from forming on the sensor, keeping the measurement accurate during condensation events.
Warmed probes can also operate at temperatures and humidity levels where wet bulb measurement is not effective.
RH sensors must come into contact with the gas that they measure.
Sensor drift and loss of measurement accuracy may occur when the functional elements of RH sensors change their properties during contact with incompatible gases.
Vaisala has developed a sensor purge function that protects the most important functional element of the sensor.
During sensor purge, the RH sensor is temporarily heated to over 100ºC, causing the sensor to outgas molecules that may be responsible for measurement inaccuracy.
Extremely dry environment
Some environmental tests call for very low humidity levels that may be 3% RH or lower.
Most instruments that are specified for use over 0 to 100% RH do not perform well near 0.
In fact the desired measurement parameter is often no longer RH, but dewpoint temperature, or parts per million by volume (ppmv).
Vaisala’s Drycap instruments can reliably measure water vapour levels as low as -80ºC dewpoint.
Measurements can be reported as dewpoint, ppmv, or a number of different parameters.
Verifying high RH
Test chambers need to be checked occasionally for correct operation at high humidity. This is difficult when the chamber is running at conditions that create a dewpoint temperature higher than ambient temperature.
Test probes at ambient temperature, when inserted into the chamber will become covered with condensation resulting in inaccurate measurements.
Vaisala offers RH sensors that incorporate a sensor pre-heat function.
Before insertion into the high RH environment, the pre-heat function is activated to raise the temperature of the sensor well above the chamber dewpoint temperature.
When the probe is inserted into the chamber, it cools to the chamber temperature, making an accurate measurement of RH and temperature within minutes.
Pressure, RH and temperature
Vaisala offers a measurement device for use when pressure, relative humidity and temperature parameters need to be monitored simultaneously.
These RH measurement devices are especially useful when the humidity parameter of interest is pressure-sensitive.
These pressure-sensitive parameters are calculated and displayed in real-time, using the integrated pressure measurement devices.
Test and calibration
Users of chambers often need a tool to verify chamber conditions or calibrate the operating sensors within the chamber.
Vaisala’s MI70 measurement system is a range of portable test instruments that provide a simple graphical user interface and a family of probes to measure temperature, high RH, low RH, low dewpoint, and carbon dioxide concentration.
Probes can be equipped with sensor pre-heat and sensor purge. Data from all measurements can be viewed graphically, stored on the MI70 or transferred to a PC.
MI70 can be directly connected to other Vaisala sensors, allowing for a fast and simple calibration interface.