“Every measuring and analysis device for technical gases must be calibrated regularly if it is to function accurately”, declares Martin Bender of WITT-Gasetechnik, one of the leading providers. The manufacturers specify the interval. “An annual calibration is usually envisioned, but shorter intervals are recommended.” A so-called zero gas is initially connected for this. The device must therefore display a gas concentration of zero. If not, the display must be reset to this value by hand. A calibration gas with definite concentration is then connected, which has to be detected precisely. Only then is the proper functioning of the system ensured.
Immediately detecting malfunctions
A lot is at play: “Even a minor deviation from the target concentration of a gas mixture can lead to expensive extra consumption and defective production”, warns Bender. The human factor is problematic here: People inevitably lose practice if there are long time intervals when calibrating manually – a potential source of error. Moreover, the practice whereby expensive service charges mostly have to be paid for rented gas systems if a technician has to be called out also pushes up costs. “The comparatively low one-off costs of an automatic calibrating unit, which usually costs less than a single technician visit, are hardly significant in comparison.”
How does the automatic calibration function in practice? One cylinder each of zero and calibration gas is connected to the analysis device. They remain there permanently and only have to be changed at very long intervals. In the case of gas mixers, the zero gas is omitted as it is taken directly from the mixer. The actual calibration system comprising three solenoid valves and a control unit is also connected. This tests the gas system in freely definable intervals. As and when required, it calibrates automatically and indicates potential malfunctions in the display. That means the user can play things safe: The gas system is always in the best condition, the test unit is amortised in the shortest time and qualified personnel are no longer necessary.
Not all manufacturers offer automatic calibration systems. The mixing, metering and control systems as well as analysis devices and flashback arrestors provided by the German manufacturer WITT for all common gases are regarded as advanced. Most systems in question can be equipped with automatic calibration systems. Because the digital controllers used have been developed by the company itself, the manufacturer achieves an outstanding accuracy and reliability. Further information at www.wittgas.com in the Internet.
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