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The most reliable method to test the sensor system is to inject a known concentration of test gas, as during calibration, and observe the reading and alarms.

In all analyzer systems, there is a possibility of undetected faults which might disable the analyzer's safety function. Therefore the greater the frequency of calibration and test, the lower the probability of an undetected analyzer fault. 

Automated test and calibration features in computer-based analyzer systems economically allow increased frequency of calibration and test, increasing reliability. 

While programmable controls and computers provide a great degree of convenience, unless these controls can be shown to conform to strict standards for the use of programmable devices in safety systems, it is preferable to use hard-wired connections for the critical alarm and analyzer malfunction signals. 

In normal uses, most analyzers will require adjustment to their sensitivity to make up for a gradual reduction in sensitivity over time. 

The normal amount of adjustment of the signal should be well understood by the maintenance personnel so that problems other than loss of sensitivity are not corrected by the improper use of the "span" adjustment. 

For Example:

An alarm which activates when the rate of increase in solvent concentration exceeds the rate alarm level, can give early warning when a severe upset condition exists that is likely to eventually result in a very high solvent concentration. 

Because the alarm triggers on a change in reading per second, and not a reading level, the rate alarm can activate at the very beginning of the analyzer's response time rather than several seconds or more later when the reading has finally climbed above the warning or danger alarm levels.