Reasons why gas detector readings are negative
A gas detector is a device equipped with a highly sensitive sensor that can keenly detect small amounts of harmful gases and combustible gases commonly found in the air. It is a type of equipment that currently needs to be assembled in various fields of industrial production. The use of sophisticated gas detectors can remind you of the risk of gas exceeding the standard at any time and ensure the safety of workers. But when using a gas detector, sometimes the reading is negative. So what is the reason for the negative reading of the gas detector?
1. Return the reading to zero in a polluted atmosphere:
Negative sensor readings often occur when the instrument is "zeroed" in a polluted atmosphere where a small amount of the sensor's target gas is present. When the instrument is later placed in a clean air environment, the sensor will show a negative reading corresponding to the contaminant concentration at that time when the device was zeroed. For example, if the carbon monoxide concentration is 5 PPM when the sensor is zeroed, when the sensor is returned to clean air, the reading will be -5 PPM.
2. Negative cross interference:
Negative readings can also occur when the sensor is placed in a gas that produces negative cross-interference. If a sulfur dioxide sensor, which normally has -100% cross-interference with nitrogen dioxide, is placed in 2 PPM of nitrogen dioxide, the sulfur dioxide reading on the instrument will be -2 PPM.
3. Pressure changes:
If the pressure changes drastically (such as when passing through a gas lock), the gas detector reading may temporarily fluctuate, which may cause the detector to sound an alarm. When the oxygen volume percentage remains stable at around 20.8%, and the overall pressure drops significantly, the oxygen for breathing in the environment may become dangerous.
4. Humidity changes:
If the humidity changes significantly (such as when going from a dry, air-conditioned environment to a humid outdoor air environment), the water vapor in the air will drive away oxygen, causing the oxygen reading to drop by up to 0.5%. The gas detector is equipped with a special filter to eliminate the impact of humidity changes on gas readings. This effect is not noticeable immediately, but slowly affects oxygen levels over several hours.
5. Temperature changes:
The gas detector is temperature compensated. However, if the temperature fluctuates drastically, the gas detector reading may drift. Instruments should be zeroed at the job site to minimize the effect of temperature changes on readings.
