How is the gas detector calibrated?
A gas detector is an instrumentation tool for gas leakage concentration detection, including portable gas detectors, fixed gas detectors, etc. It mainly uses gas sensors to detect the types of gases that exist in the environment. Gas sensors are used to detect gases. Composition and content sensors.
Gas detectors can detect gas leakage, and remind people to take safety measures such as evacuation, forced ventilation, and shutdown of equipment by sending out alarm signals such as sound and light. It is an indispensable instrument in industrial production and daily life.
But the gas detector is not always able to accurately measure the gas concentration, just like our watch needs to be calibrated regularly and the standard time, the gas detector also needs to be calibrated regularly to ensure the accuracy of the detection, and the calibration process is called for "calibration".
The accuracy of the combustible gas alarm is an important prerequisite for detecting and issuing an alarm, 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 conditions in the environment during use. Due to the influence of substances, it gradually changes or even becomes invalid due to poisoning. Only through timely maintenance and calibration can the accuracy of the results detected by the instrument be guaranteed.
In actual use, many factors will affect the accurate value of the alarm. Regular calibration is to minimize the error of the test results and achieve the highest accuracy.
1. Oxygen concentration is too high or too low
Detecting combustible gases in an atmosphere with insufficient oxygen may cause the concentration of combustible gases to be lower than the actual concentration; conversely, when testing in an environment with sufficient oxygen, the detected concentration may be higher than the actual concentration.
In this case, it is necessary to calibrate the detector to achieve accurate measurement.
2. Recalibration of combustible gas detector
When the gas concentration is too high and the combustible gas detector displays "over range", recalibration is required. For example, in the process of using a combustible gas detector, the measuring range of the instrument is 0-100% LEL, and the actual concentration is higher than 100%, which will cause an over-range phenomenon. At this time, the gas detector needs to be calibrated again .
Water vapor or other known impurities in silicone compounds may interfere with the proper operation of combustible gas detectors, causing their readings to be lower than the actual gas concentration. If the instrument has been used in the water vapor environment of silicone compounds, in order to ensure the accuracy of the measurement, the instrument should be re-calibrated before the next use.
According to the lower explosion limit of each detected gas, we need targeted calibration.
Taking the hydrogen alarm as an example, we must first complete the production of hydrogen standard gas, and age the gas sensor or application product under rated working conditions for a period of time (generally not less than 2 hours, preferably more than 24 hours) to make the element The resistance value is sufficiently stable. Put the gas sensor or application product of the detector into the test chamber, and inject the gas or liquid to be tested into the test chamber with a sampler (medical syringe) according to the volume requirement to form a calibration gas sample. Adjust the circuit preset mechanisms such as variable resistors on the application product to make the application product just trigger (such as alarm). Exhaust the test gas from the test chamber with an exhaust fan, repeat 2-4 times, and confirm that the applied product is just triggered.
When calibrating the gas detector, pay attention to the following items:
1. Calibrate the environmental conditions. The gas alarm is an electronic instrument, and the error in its verification mainly comes from the verification environment. It is required to be well ventilated, and the measured components will not be disturbed during calibration, and its environment and temperature need to reach a certain value.
2. Calibration flow control. Because gas alarms are mostly catalytic combustion sensors, the flow rate directly affects the accuracy of the test results, so the flow rate needs to be controlled. If the flow rate is too large or too small, it will affect the calibration result.
3. During calibration, the indication values of the main controller and the on-site detectors do not match. When the gas concentration of the gas detector in the environment reaches or exceeds the preset alarm value, the main controller will send out an alarm to remind the on-duty personnel to take safety measures, so as to ensure the safe production of the enterprise.
4. Calibration cover for calibration. When calibrating flammable and toxic gas alarms, a calibration cover will be used. Each manufacturer has its own dedicated calibration cover. When calibrating, it is better to use the calibration cover produced by the original factory, and the calibration results will be more accurate. In addition, in order to ensure the accuracy of detection, the gas alarm should be calibrated at least once a year.
