The Trouble With Humidity

??From the September 2010 – Vaisala Knowledge eNewsletter

The Hidden Challenge of RH Calibration, by Rick Schellenberg of Veriteq, a Vaisala Company

Vancouver BC, Canada –?? A year after installation, the new high-accuracy relative humidity transmitters are removed from service and returned to the lab for routine testing and recalibration. A few days later they return, more out of calibration than ever before. But nobody notices…at first.

Sound impossible? Well, it happens more often than you think. Humidity calibration is difficult and there is plenty that can go wrong.

RH is troubling because it is a temperature-dependent variable. Its value can change significantly with even slight variations in temperature and without any increase in moisture.

For example, a 1 ??C?? variance in temperature at 20 ??C and 50 % RH can introduce an error of ?? 3 % RH, an enormous variance in a calibration process.

At 90 % RH, even a 0.2 ??C variance will result in a ?? 1% RH error.

These temperature effects highlight the importance of thermal stability, a condition that is often difficult to achieve in a calibration environment.

This article (Download PDF Version by clicking here) will help companies examine their own calibration processes and assess how they measure up to today???s demanding requirements.

Veriteq, a Vaisala company, is the leader in Environmental Monitoring & Validation solutions for Temperature, Humidity and other parameters.

Veriteq Instruments, Inc.
13775 Commerce Parkway
Richmond, BC Canada V6V 2V4

Tel: +1 (604) 273-6850