Sensor calibration
The most common fault of combustion-type sensors is due to exposure to specific
Performance degradation caused by exposure to toxins. Therefore, all gas monitoring systems should not only be calibrated during installation but should also be periodically checked and recalibrated as necessary; these steps are essential. Checks must use precisely calibrated standard gas mixtures, so that the zero and 'span' levels on the controller can be correctly set. Standards like EN50073:1999 can provide guidance for calibration regarding check frequencies and alarm level settings. Generally, checks should be conducted weekly at first, but this interval may be extended once operational experience is gained. When two alarm levels are needed, these are usually set at a lower limit of 20–25% LEL and an upper limit of 50–55% LEL. Early (and low-cost) systems required two people for checking and calibration, where one person was responsible for exposing the sensor to the gas flow, and the other for verifying the readings displayed on the sensor control unit. Then, the zero and span potentiometers on the controller are adjusted until the readings fully correspond to the concentration of the gas mixture.
Remember, when adjustments must be made inside a flameproof enclosure, the power must first be disconnected, and permission must be obtained to open the enclosure. Nowadays, many 'single-person' calibration systems are available on the market, allowing the sensor itself to perform the calibration procedure. This greatly reduces maintenance time and costs, especially for calibrations in locations that are difficult to reach, such as offshore oil or gas drilling platforms. Alternatively, some sensors now available are designed to meet intrinsic safety standards, making it possible to perform calibration conveniently away from the site, such as at a maintenance station. Because they are intrinsically safe, these sensors can be freely exchanged when replacements are needed at the site without having to shut down the system for safety reasons beforehand. Therefore, maintenance can be performed on a 'live' system, making it faster and cheaper than earlier conventional systems.
Need help?
For selection advice, please Contact us or Online inquiry.