The most common error with catalytic sensors is reduced efficiency due to exposure to certain inhibitors and toxins. It is therefore important that diagnostics and calibration are performed regularly on the gas detection system. Diagnosis must be performed using standardized gas mixtures to precisely adjust the gas detection ranges on the detector.
Standards such as EN 60079-29-2 provide a brief overview of the legal regulations for the calibration of flammable gas detectors and instructions for the calibration of toxic gas detectors. In general, detector functionality checks are done on a weekly basis. When it is necessary to set alarm values for gas, a value between 20-25% of the lower explosive limit (% LEL) is taken for the lower limit and 50-55% of the upper explosive limit for the upper value.
Older and cheaper systems require the work of two people to inspect and calibrate, one to release the appropriate gas and the other to monitor the gas concentration. The values of the detection range on the transmitter are adjusted until it is equal to the values on the certified gas mixture.
Today, many calibration stations are available that allow the calibration to be performed on the sensor itself. This drastically reduces maintenance time and cost especially when sensors are difficult to access, such as offshore and gas platforms. Alternatively, sensors designed for intrinsically safe atmospheres are available so it can be calibrated at a convenient location outside the plant.