The typical ammonia (and other refrigerants) leak detection system consist of one or more sensors communicating to a readout or display. Internal in the sensor is a “cell” that picks up the ammonia in the environment and provides the initial signal to the sensor electronics and ultimately to the readout device. This cell has a limited lifespan and its sensitivity diminishes over time until it is finally no longer functional. The typical useful life of the cell in an electro-chemical sensor such as the Honeywell Analytics (Manning) EC-F9 series is 2 – 4 years. This life is shortened if the sensor is in a warm space (greater than 75°) like compressor rooms, or has been exposed to high concentrations of ammonia. Because the cell deteriorates with time and environment, the sensor needs to be re-calibrated on a regular schedule. Manning and other manufacturers specify that their sensors be calibrated on six month intervals. Calibration is accomplished with the use of calibrated gas and a calibration kit. It is a relatively easy procedure; simply apply the test gas to the sensors, measure the sensor output, and make necessary adjustments to the sensor’s calibration “pot”. Be sure to make a record of the re-calibration. If the proper output cannot be obtained the cell in the sensor needs to be replaced. Once a replacement cell has been installed the sensor will need to be calibrated. In rooms or areas that are considered to be “critical” it is good practice to test the response of the sensor more frequently than the six month calibration period. To test the response you can use the test gas or a water/ammonia solution. If you want to use the water/ammonia method simply soak a cloth with the solution and hold it up to the sensor cell. The readout should indicate a response to the ammonia.
