
Air Quality & Gas Detection

Air quality and gas detection are critical for the health and safety of personnel working in a wide range of industries. Gas detectors can monitor and alert workers to the potential danger of explosions caused by combustible gases, poisoning by toxic gas exposure and asphyxiation due to lack of oxygen. Gas monitoring systems can automatically initiate an action if dangerous levels of gases are detected, such as turning on ventilation fans, shutting down a gas valve, or activating alarms for evacuation of personnel.
Gases can be inert, oxidizers or flammable. Inert gases are not combustible and are sometimes used in fire suppression. Helium and carbon dioxide are inert gases. Oxidizers are not flammable on their own, but will act as an oxidant and aid in combustion. Chlorine and oxygen are oxidizers. Flammable gases can be explosive when mixed in the right proportions with air. Methane, ethylene, butane and hydrogen are flammable gases.
Toxic gases can be produced from petroleum processing and chemical manufacturing. Depending on the level of exposure, toxic gases can cause everything from mild irritation to death. Carbon monoxide, hydrogen fluoride, hydrogen sulfide and volatile organic compounds are all considered toxic gases that need to be monitored.
Low oxygen conditions can occur in some working or underground environments and can result in dizziness, fainting or death. Displacement of oxygen by another gas or consumption of oxygen by a biological or chemical process can lead to low oxygen levels. A normal oxygen level in the atmosphere is 21 percent volume. An oxygen gas detector can be set to trigger an alarm at 19.5 percent volume.
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Digital signals are represented in either a true or false. There is no gray area with digital signals. An example of this might be a light switch. A light switch is either on or off. Another example of this might be a motor that is running or not running. Digital signals can be generated with both AC and DC circuits with varying voltages, currents and resistance. Some practical examples of using digital signals in an industrial environment might be if a pump is running or not running or a whether a valve is open or closed.
Analog signals convey information in the form of a range. A light switch might be on or off as a digital signal, but a dimmer switch would be an analog signal. It can be on or off, but it can also be somewhere in between. A practical example of using analog signals in an industrial environment would be if there is a need to measure the level of a tank; whether it's full, empty or somewhere in between. Analog signals can take many different forms with some of the more common being a 4 to 20 milliamp signal or a 0 to 5 or 0 to 10 volt signal.
Communication in a device can either be sent or received. Whether that data is sent or received depends on the type of information. Is there a need to monitor the status of something? If so, an input needs to be received about that information. Is there a need to control something? If so, an output needs to be sent about what needs to occur. Receiving inputs and setting outputs are both things that can be accomplished by using both digital and analog signal types. Therefore, the signals are referred to as analog outputs (AO), analog inputs (AI), digital inputs (DI) or digital outputs (DO).