An introduction to the calibration methods used for gas detectors
Gas detector is currently a detection instrument specifically designed for hazardous environments and confined space entry detection. It can be said to be one of the economical and efficient gas detectors. However, in the use of gas detectors, it is necessary to regularly calibrate them. Why do we need to regularly calibrate gas detectors? The main reason is that the instrument may drift during long-term use, leading to excessive error accuracy and inaccurate measurement results, which affects the safety warning function of the gas detector.
1. Alarm function
Inject a gas standard substance with a concentration of about 1.5 times the alarm set value to the gas detector, observe whether the instrument's sound, light, or vibration alarm function is normal, and record the alarm concentration value displayed by the instrument, which is the alarm action value.
2. Indication error
Inject three different concentrations of gas standard substances into the gas detector and record the measurement results of the gas detector separately. Repeat the detection steps for each concentration three times, and calculate the relative and absolute errors of the instrument using formulas based on the difference between the average value of the instrument's detection results and the actual gas concentration introduced.
The concentrations of gas standard substances introduced for indication error verification are:
Ex.: 10%, 40%, and 60% of full scale gas standard substances
H2S: 20%, 50%, and 80% of full scale gas standard substances
O2: 20%, 50%, and 80% gas standard substances of full scale
CO: Gas standard substances with 1.5 times instrument alarm (lower limit) set value, 30% measurement range upper limit value, and 70% measurement range upper limit value
3. Response time
Firstly, zero point gas is introduced to calibrate the instrument; Secondly, introduce a certain range of concentration (Ex.: 40% of full scale; H2S: 50% of full scale) to the instrument; O2: 80% of full scale; The gas standard substance (CO: 70% of the upper limit of the measurement range) should be removed after the gas detector stabilizes; Then introduce zero point gas again to stabilize the instrument; Finally, add the gas standard substance with the above concentration and record the time from the introduction to the stable display of 90% of the above concentration on the instrument using a stopwatch. Repeat three times and take the average value to obtain the instrument's response time.
4. Repeatability
After the gas detector is preheated and stabilized, adjust the zero point of the instrument with zero gas and introduce a certain range of concentration (Ex: 40% of full range; H2S: 50% of full range) to the instrument; O2: 80% of full scale; CO: gas standard substance with a measurement range of 70% of the upper limit value, and record stable measurement data. Repeat the operation 6 times, and the relative standard deviation of a single measurement is the repeatability of the instrument.
