What is the working principle of the gas detector sensor?
Gas detectors can detect gas leaks and alert people to take safety measures such as evacuation, forced exhaust, and equipment shutdown by issuing audible and visual alarm signals, which is an indispensable instrument in industrial production and daily life. But gas detectors are not always able to accurately measure the gas concentration, just like our watches need to be regularly calibrated with the standard time, gas detectors also need to be regularly calibrated to ensure the accuracy of detection, and the calibration process is called "calibration".
01 Why Calibration is Needed
The accuracy of the combustible gas alarm is an important prerequisite for detecting and issuing alarms, and its accuracy depends on the built-in combustible gas sensor, whether it is an electrochemical sensor or a catalytic combustion sensor, it will be affected by certain substances in the environment during use, and gradually change or even poisoning failure, only after timely maintenance and calibration, the accuracy of the results detected by the instrument can be Only after timely maintenance and calibration, the accuracy of the instrument's detection results can be guaranteed. In actual use, many factors can affect the accuracy of the alarm, regular calibration is to minimize the error of the detection results, the accuracy of the highest.
02 Which cases need to be calibrated
1、Oxygen concentration is too high or too low
Detection of combustible gases in an atmosphere with insufficient oxygen may cause the concentration of combustible gases to be lower than the actual concentration; conversely, detection in an environment with too much oxygen may result in a higher concentration than the actual concentration. In this case, it is necessary to calibrate the detector to achieve the purpose of accurate measurement.
2, combustible gas detector recalibration
When the gas concentration is too high, resulting in combustible gas detector display "over range", it is necessary to recalibrate. Such as in the use of combustible gas detectors, the range of the instrument is 0-100% LEL, while the actual concentration is higher than 100% will cause the phenomenon of over-range, this time it is necessary to recalibrate the gas detector. Water vapor or other known impurities of silicone compounds may affect the proper operation of the combustible gas detector, resulting in a lower reading than the actual gas concentration. If the instrument has been used in a water vapor environment with silicone compounds, it is also important to recalibrate the instrument before the next use to ensure accurate measurements.
03 How to calibrate
Depending on the lower explosion limit of each detected gas, we need to calibrate the instrument in a targeted manner. Take the hydrogen alarm, we first need to make the standard gas of hydrogen, the gas-sensitive components or application products in the rated operating conditions of power aging for a period of time (generally not less than 2 hours, preferably more than 24 hours) to make the component resistance value fully stable. The gas-sensitive components of the detector or application products into the test chamber, according to the volume requirements with a sampler (available medical syringe) inject the gas or liquid to be tested in the test chamber to form a calibration gas sample. Adjust the circuit presetting mechanism such as variable resistance on the application product to make the application product just trigger (such as alarm). Exhaust the test gas from the test chamber with the exhaust fan and repeat 2-4 times to confirm that the application is triggered.
04 Calibration precautions
Gas detector in the calibration to pay attention to the following matters.
First, the calibration of environmental conditions. Gas alarm is an electronic instrument, the error in its calibration mainly from the calibration environment. Requires good ventilation, and will not be disturbed by the measured components during calibration, its environment and temperature need to reach a certain value.
Second, the calibration flow control. As gas alarms are mostly catalytic combustion sensors, the size of the flow rate directly affects the accuracy of the calibration results, therefore, the flow rate needs to be controlled. The flow rate is too large, or too small, will affect the calibration results.
Third, the main controller and the field detector do not match the indicated value during calibration. When the concentration of gas detector gas in the environment reaches or exceeds the preset alarm value, the main controller will issue an alarm to remind the duty personnel to take safety measures so as to protect the safety production of the enterprise.
Fourth, the calibration hood for calibration. In the calibration of combustible, toxic gas alarms, will use the calibration hood, each manufacturer has its own special calibration hood, in the calibration, it is best to use the original production of calibration hood is better, calibration results will be more accurate. In addition, to ensure the accuracy of detection, gas alarms are calibrated at least once a year.
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