Understanding Sensors
When you purchase a gas meter, you specify the type and number of sensors to have installed based on the hazards in your work area. Most sensors are filled with a chemical solution that reacts to the target gas and produces a small electrical current that the instrument reads and converts to a number on the display. These sensors are called electro-chemical sensors. They are usually specific to the target gas and are the most accurate method for real time measurements. Some of the electro-chemical sensors that we can provide measure oxygen, carbonmonoxide, hydrogen sulfide, sulfur dioxide, chlorine and ammonia, just to name a few.
Combustible gas sensors use a catalytic bead which heats up and burns the sample to determine the amount of combustible gas present. Typically this sensor is referred to as an LEL sensor. LEL stands for Lower Explosive Limit and when you reach 100% LEL, you have the right conditions for a fire or explosion.
LEL sensors will respond to many different combustible gases (methane, propane, acetylene, hydrogen, etc), therefore it is important to understand what your specific gas of interest is and how it relates to the combustible gas you use during calibration. A correction factor may be required.
Make sure the meter you select has the ability to apply correction factors.
Finally, the last type of sensor that we can provide measures Volatile Organic Compounds. These are the compounds found in fuels, degreasers, paints and solvents. These are best measured with a PID; Photo Ionization Detector. If you have to measure VOC’s in your work area, we have gas detection instruments that are strictly PID’s and meters that are both a multigas meter plus PID.
Be aware that some electro-chemical sensors can be cross sensitive to other gases. For instance, carbonmonoxide sensors will show a reading in the presence of hydrogen. Knowing about cross sensitivities in the beginning will help you to properly interpret the readings from your portable gas detection instruments. Also, PID’s and LEL sensors can respond to a wide range of gases, not just one or two like with electro-chemical sensors. It is important to understand the gases that could be present in your work area in order to choose the correct sensors and understand their limitations. Here are some more in-depth documents that can help you understand sensor.
- TN106: Correction Factors, Ionization Energies and Calibration Characteristics
- TN114: Sensor Specifications and Cross-Sensitivities
- TN121: CO Sensor Cross-Sensitivities and Removal with Charcoal Filter
- TN144: Handling LEL Sensor Poisoning
- TN156: Correction Factors for Combustible Gas (LEL) Sensors
Back to Gas Detection Instruments