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| How far apart should the sensors be? What should the mounting height of the sensors be? Are there other considerations for locating sensors? What gases can be detected with Critical Environment Technologies equipment? Are some gases heavier or lighter than others? What are the molecular weights of gases? Are there many types of sensors used for gas detection? Why are different kinds of sensors used? What are the advantages and disadvantages of Solid State (MOS) sensors? What are the advantages and disadvantages of Electrochemical sensors? What are the advantages and disadvantages of Catalytic sensors? What are the advantages and disadvantages of Infrared sensors? What are the advantages and disadvantages of Galvanic sensors? Does gas detection equipment need maintenance and calibration? Can gas detection equipment produce energy savings? I get confused between CO and CO2 — what’s the difference? Where do NO and NO2 come from? Where are the different transmitters used? What are the most common commercial and institutional applications? What gases are present in parking garages? What gases are present in arenas? What gases are present in swimming pools? What gases are present in chiller rooms? What gases are present in warehouses? What gases are present in repair garages?
How far apart should the sensors be? This depends on the application, but for most commercial applications, each sensor should ‘cover’ 5,000 to 7,000 square feet. This translates to about 70 to 80 feet apart, or a 35 to 40 foot radius. In more hazardous areas, the sensor coverage area should be reduced. What should the mounting height of the sensors be? This depends on the density of the gas relative to air. Heavier than air gases should be detected 6 inches from the floor, than air gas sensors should be placed on or near the ceiling, and gases which have a density close to that of air should have sensors installed in the ‘breathing zone’ 4 to 6 feet from the floor. Consider accessibility for calibration when locating sensors. Are there other considerations for locating sensors? Sensors should not be placed near ventilation fans or openings to outside. They should be placed in areas where there is good air circulation, but not in the path of rapidly moving air. Pay particular attention to ‘dead air spots’ where there is little or no air movement. The breathing zone refers to the area 4 to 6 feet from the floor, where most human breathing takes place. This is a good default location for sensors. What gases can be detected with Critical Environment Technologies equipment?
Don’t see what you’re looking for? There are more….contact us! Are some gases heavier or lighter than others? All substances have a molecular weight determined by the number and type of atoms in the molecule. In a gaseous state, the larger and heavier the molecule, the heavier the gas. What are the molecular weights of gases? Molecular weight of some common gases:
Are there many types of sensors used for gas detection? There are many sensors used to detect gases. Some gases can be detected by some sensors and not by others, and some sensors are more accurate or gas-specific than others. Types of sensors include Solid State (also known as Metal Oxide Semiconductor), Electrochemical, Catalytic, Infrared, Galvanic, Photoaccoustic, PID and others. Why are different kinds of sensors used? Most gases can only be detected by one or two sensor types. Then consideration is given to required accuracy and specificity, sensor life expectancy, and finally cost. What are the advantages and disadvantages of Solid State (MOS) sensors? Advantages: Low cost, long life, quite resistant to poisoning Disadvantages: Broad spectrum, non-specific, not as accurate as other types What are the advantages and disadvantages of Electrochemical sensors? Advantages: Accurate, repeatable, more gas specific, defined cross sensitivities Disadvantages: Relatively short life, moderately expensive What are the advantages and disadvantages of Catalytic sensors? Advantages: Range 0 — 100% LEL for many combustible gases, accurate, long life Disadvantages: Moderately expensive, can be poisoned What are the advantages and disadvantages of Infrared sensors? Advantages: Very gas specific, best way to detect CO2, very accurate & stable, long life Disadvantages: Expensive What are the advantages and disadvantages of Galvanic sensors? Advantages: Range 0 to 100% volume Oxygen, long life Disadvantages: Expensive, poor low-end accuracy Does gas detection equipment need maintenance and calibration? Yes. Maintenance on a properly installed, quality system is minimal and need only consist of a visual inspection and verification of operation. Calibration frequency depends on sensor type and application. Typical frequency for commercial applications is 1 to 2 times per year. For areas where health hazards may exist, 3 to 4 times per year. Industrial applications 4 to 6 times per year or even monthly. Instrument calibration refers to exposing the instrument to a known quantity of the measured substance (real or simulated) and resetting the instrument if required. This verifies that the instrument is operating properly and adjusts for any sensor drift. For gas detection equipment this involves exposing the sensor to a known concentration of the target gas, usually from a calibration gas cylinder, and resetting the instrument to adjust for sensor drift. Can gas detection equipment produce energy savings? Yes. A properly installed, maintained and calibrated gas detection system can produce significant energy savings by running ventilation fans only when required, minimizing energy usage and expense. Cross-sensitivity refers to the response of a sensor to a gas other than the target gas (also called an interference gas). Combustible gases are those that are monitored because they present a risk of explosion or fire. Usually occurs as a product of combustion of an organic compound. Most commonly found in vehicle exhaust. I get confused between CO and CO2 — what’s the difference? CO is the chemical symbol for Carbon Monoxide which usually comes from vehicle exhaust in commercial applications. CO2 is the chemical symbol for Carbon Dioxide which usually comes from human respiration in commercial applications and is used as an indicator for Indoor Air Quality. Where do NO and NO2 come from? Nitric Oxide (NO) and Nitrogen Dioxide (NO2) usually occur as a byproduct of combustion, often from vehicle engines. (see Nitrogen Oxides) Nox is an abbreviation for Nitrogen Oxides. (see Nitrogen Oxides) A group of compounds most commonly found in vehicle exhaust, where Nitrogen Oxides are a byproduct of combustion formed from the Nitrogen and Oxygen in the air. In exhaust, the most common is Nitric Oxide (NO) followed by Nitrogen Dioxide (NO2). Other Nitrogen Oxides found in much smaller quantities are N2O, N2O3, N2O4, N2O5, N3O4 AND NO3. Carbon Dioxide is a naturally occurring gas in air (less than 1 %) and since it is exhaled during respiration, it is often used as an indicator of Indoor Air Quality. CO2 is produced in the combustion of organic compounds and it is also formed during fermentation. CO2 is used in many industrial and food & beverage applications and may present a hazard if it leaks from cylinders. Hydrogen Sulphide is commonly produced from decay of organic matter and in industrial processes such as Pulp & Paper and Oil & Gas. It is often found in ‘Sewer Gas’. Combustible gases form flammable mixtures with air. For each gas there is an explosive range within which the fuel to air mixture will support combustion. LEL is an abbreviation for Lower Explosive Limit, which is the minimum concentration of each gas in air that must be present for combustion or explosion to occur. % LEL refers to a method of measuring the concentration of a combustible gas where the range of the sensor is set to correspond with the concentration of gas that is below the explosive range. In this case the Lower Explosive Limit equals 100 % LEL. Parts Per Million. 100 % volume equals 1,000,000 ‘parts’ , 1 % volume equals 10,000 ‘parts’ . The percentage of a gas in the total volume of air. Where are the different transmitters used? What are the most common commercial and institutional applications? What gases are present in parking garages? Vehicle exhaust gases: CO, Nitrogen Oxides What gases are present in arenas? Zamboni exhaust gases: CO, Nitrogen Oxides What gases are present in chiller rooms? What gases are present in swimming pools? Water purification chemicals: Chlorine, Ozone What gases are present in warehouses? Forklift or truck exhaust gases: CO, Nitrogen oxides What gases are present in repair garages? Vehicle exhaust gases: CO, Nitrogen Oxides | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||