|Alarm is an audible, visual, or physical presentation
designed to warn the instrument user that a specific level of a dangerous gas/vapor
concentration has been reached or exceeded.
Alarm Module is an epoxy encapsulated device which controls the output of the FuelGuard system. The Alarm Module provides connectors for four Leak Detection Modules. (If more than four sensors are attached an Expansion Module is also required.) The Alarm Module provides power to the electronics in the enclosure. The power is fused by a standard automotive 3 amp "minifuse" to protect the components. The Alarm Module interprets the output of the Leak Detection Modules and activates the relays and the annunciator indicator lights. The Alarm Module provides four independent (single pole/double throw) two amp relays, one for fail, and three for gas alarms. These relays don't have to be wired for the Alarm Module to function but they are intended to operate external signaling devices such as horns and lamps or to affect controls such as ignition interlocks. Connection to these relays is done through four push-on connectors that go on the left side of the Alarm Module. The supplied wiring is color coded. The three gas alarm relays (trace, moderate & significant) are normally energized or normally de-energized. Thus when an alarm condition occurs, the relay coil is energized, the relay contacts are pulled in and the common contact is connected to the NO contact. (See FuelGuard Drawing)
Alarm Set Point is the selected gas concentration level where an alarm is activated.
Ambient Air is air to which the sensing element is normally exposed.
Calibration Gas is the known concentration(s) of gas used to set the instrument span or alarm level(s).
Combustion is the rapid oxidation of a material evolving heat and generally light.
Consumables are those materials or components which are depleted or require periodic replacement through normal use of the instrument.
Diffusion is a process by which the atmosphere being monitored is transported to the gas-sensing element by natural random molecular movement. This movement is accelerated by thermal energy.
Explosion is an uncontrolled chemical reaction which generates a large amount of heat and gas in a short period of time.
Fail Safe. Any system that cannot fail in any mode without providing a directly observable indication of failure. Consider an electrical relay with a set of contacts that are open when it is un-powered. If a power source and a light bulb are connected in series with the contacts, the lamp will glow when the relay is energized. If the goal of this system is to insure that the relay has power, then this system is said to be fail safe. If the lamp, relay contacts, lamp power source relay coil, or the relay coil power supply fail, then the lamp extinguishes itself providing a directly observable foolproof indication of failure.
Flameproof or ExplosionProof
Flashpoint is the minimum temperature at which a liquid gives off a sufficient vapor to reach 100% LEL (sufficient vapor to form an ignitable mixture with the air near the surface of the liquid).
Flammable (Explosive) Limits. For gases or vapors which form flammable mixtures with air or oxygen, there is a minimum concentration of vapor in air or oxygen below which propagation of flame does not occur on contact with a source of ignition. There is also a maximum proportion of vapor or gas in air above which propagation of flame does not occur. These boundary-line mixtures of vapor or gas with air, which if ignited will just propagate flame, are known as the "lower and upper flammable limits" (LFL and UFL) or the "lower and upper explosive limits" (LEL and UEL), and are usually expressed in terms of percentage by volume of gas or vapor in air. LEL and LFL are different terms for the same concept and can be used interchangeably. In popular terms, a mixture below the lower flammable limit is too "lean" to burn or explode and a mixture above the upper flammable limit too "rich" to burn or explode.
Flammable (Explosive) Range. The range of flammable vapor or gas-air mixture between the upper and lower flammable limits is known as the "flammable range", also often referred to as the "explosive range". For example, the lower limit of flammability of acrylonitrite at ordinary ambient temperatures is approximately 3 percent vapor in air by volume, while the upper limit of flammability is about 17 percent. All concentrations by volume of acrylonitrite vapor in air falling between 3 percent and 17 percent are in the flammable or explosive range.
The FuelGuard System is composed of three major components: The Alarm Module, Leak Detection Modules with display and Sensors. Sometimes a system is attached to an Annunciator (not pictured). The Alarm Module and the Leak Detection Modules (one for each sensor) are housed in a NEMA 4X enclosure which protects them from dirt and water. The sensors and the Annunciator are connected to the electronics in the enclosure by automotive connectors. See FuelGuard Drawing.
|Gas is a phase of matter which expands indefinitely to fill a
containment vessel. Characterized by a low density.
Gas-Sensing Element (Sensor) is the particular subassembly or element in the gas detection instrument which, in the presence of a gas, produces a change in its electrical, chemical, or physical characteristics.
Ignition Temperature is the minimum temperature necessary to initiate combustion (oxidation) and have self-sustained combustion of the solid, liquid, gas, or vapor of interest.
Ignitable Mixture A mixture within the flammable range (between the lower and upper flammable/explosive limits) that, when ignited, is capable of the propagation of flame away from the source of ignition.
Leak Detection Module is an epoxy encapsulated module which controls the operation of an attached sensor, displays its reading and passes information to the Alarm Module. It is usually housed in the FuelGuard NEMA 4X Enclosure. The Leak Detection Module's LED display provides a linear reading of the concentration of combustible gas the the sensor is seeing, displayed as a % of the Lower Explosion Limit (LEL). See FuelGuard Drawing.
Liquid is a phase of matter which is free to conform to a shape of a vessel but has a fixed volume and has a greater density than a gas.
Lower Explosive Limit (LEL)
Mobile refers to a continuous-monitoring instrument mounted on a vehicle such as, but not limited to, a mining machine or industrial truck.
Monitor is an instrument used for continuous measurement
of a condition which must be kept within prescribed limits.
Nonsparking Nonsparking circuits are those which contain no contacts or in which contacts are isolated from the surrounding atmosphere such as by hermetic sealing.
Portable refers to a self-contained, battery-operated or transportable gas monitor worn or carried by the person using it. A gas detector that can be carried.
Range is the series of outputs corresponding to values of concentrations of the gas of interest over which accuracy is ensured by calibration.
Span is the algebraic difference between the upper and lower values of a range.
Stoichiometric. The exact percentage of two or more substances which will react completely with each other leaving no unreacted residue. For example, a 7% mixture of methane by volume in air will react completely with the oxygen present leaving only CO2 and H2O as residue. If the methane concentration here is less than 7%, there would be oxygen left over. If the methane concentration were greater than 7%, there would be methane left over.
Threshold Limit Value Time-Weighted Average (TLV-TWA) is the time-weighted average concentration of a substance for a normal 8-hour work day and a 40-hour work week, to which nearly all workers may be repeatedly exposed, day after day. (OSHA)
Test Gas is a known concentration of the gas to be detected diluted with clean air.
Trouble Signal is a signal (contact, transfer, and/or visible or audible signal) advising an instrument user of conditions such as input power failure, an open circuit breaker, a blown fuse, loss of continuity to the detector head, defective gas-sensing element, or significant downscale indication
Vapor is the gaseous state of a material below its boiling point.
Vapor Density relates the molecular
weight of a gas to the molecular weight of air.
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