The main components of a pressure switch
Pressure switches are devices that monitor pressure using some version of a diaphragm, piston or bellows as a pressure sensor. The switch closes when it registers a certain pressure and makes an electrical contact. The switches may be designed to react to falling or rising pressure changes.
The pressure switch operates on the principle of a lever and opposing forces. There are three basic components to these switches that may be varied or added to depending on the switch application;
• A sensing element that may be a bellows, piston or a diaphragm. These components may be made from metal or any synthetic material.
• A stable spring
• A snap acting micro switch. This provides the on-off action of the switch
A chain of events takes place when pressure is applied to the switch. The diaphragm begins to flex against a pressure plate. If the pressure is sufficient to compress the spring, the pressure plate rises. It continues to rise as the pressure increases until it makes an electrical contact. The circuit closes and power is supplied within the system. The final on-off action comes from the electronic snap switch.
The operating lifetime of a pressure switch depends mostly on the nature of the pressure sensor. In general, a diaphragm is longer lasting than a bellows or a piston. But there are other factors that will affect it. High speed cycles of switching on and off should be avoided as should switching to the maximum and minimum pressure ranges. When buying pressure switches online or in store be sure to check the switch’s pressure range is larger than the pressure range of the device you will use it for. This minimizes wear and tear on the switch mechanism.
The deadband setting is another important feature of the pressure switch. This is the difference in the pressure between its activation and reactivation points. If this setting is too small, the switch will open and close in response to tiny pressure changes. This is called “chatter” in industry jargon and is a frequent cause of switch burn out. Switches can be manufactured with adjustable deadbands over 10 to 50 percent of the switch pressure range.
It’s also a good idea to be aware of the wetted part of a pressure switch when selecting one. This is the part of the switch that comes into contact with the pressure creating medium such as gas, liquid, or solid such as a finger. Most diaphragm switches use elastomers such as Mylar, nylon and Viton while bellows switches use stainless steel with a silver brazing. Piston devices generally have a carbide piston in a brass trim. Seals may also be added to diaphragm devices while synthetic materials may seal some bellows type switches.
Housing is necessary for switches that will be exposed to water, dirt or the atmosphere in general. Heavy housing is necessary in an explosive environment. Those switches with no housing are usually incorporated into panels such as on computers or smart phones.
Image Credit : http://www.flickr.com/photos/gems-sensors/8719275433/
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