Monday, November 11, 2019


Pressure switch |[pic][pi| |c] | A pressure responsive switch senses a change in pressure and responds to such changes by alternately making and breaking an electrical connection. Pressure-sensitive switches are used in a variety of applications where it is desired to switch apparatus on or off at predetermined pressures. These switches are utilized in a wide variety of applications, as in automobiles [pic] , aircrafts and in various other environments. Pressure switches include set-point pressure switches that actuate when a specified pressure is reached and pressure measuring switches that are capable of measuring the ambient pressure and reacting accordingly. A pressure responsive switch generally comprises a diaphragm responsive to a pressure change, a rigid ring for securing the diaphragm, and a pair of electrically conductive contacts that break contact based on movement of the diaphragm. Mechanical pressure switches typically provide an output signal in the form of a switch closure in response to application of mechanical or atmospheric pressure. A differential pressure switch [pic] is a device which utilizes differential fluid pressure from low and high pressure sources to actuate an electric switch at a pre-set actuation point. Differential pressure switches are commonly employed to control the operation of snap action switches. Flow switch |[pic][pi| |c] | A flow switch is used to sense the flow of a fluid passing through its valve body and to send an electrical control signal to control the switching unit. In many applications, it is essential to be able to determine whether fluid is flowing in a pipeline, duct or other conduit and to respond accordingly to such a determination. For example, flow responsive devices for producing a control signal which is used to de-energize a pump when the flow rate falls below a preselected minimum are commonly employed in systems for transferring fluid between reservoirs. Fluid flow switch sensing devices have been developed for monitoring fluid flow in pipelines, ducts, and other conduits. A flow switch produces an electrical signal which is commensurate with a preselected rate of flow of a fluid in a conduit. Various flow switches have been developed to be responsive to the flow rate of a fluid within a flow line. Usually the flow switch is connected into the flow line so that the flow path of the fluid passes through the flow switch. Several such devices rely on the pivotal movement of a rod supported blade which is deflected depending on the amount of fluid flow. Limit switch |[pic][pi| c] | Switches are commonly employed as input devices to indicate the presence or absence of a particular condition in a system or process that is being monitored and/or controlled. In motorized electromechanical systems, limit switches provide the function of making and breaking electrical contacts and consequently electrical circuits. A limit switch is configured to detect when a system's element has moved to a certain position. A system operation is triggered when a limit switch is tripped. Limit switches are widely used in various industrial applications, and they can detect a limit of movement of an article and passage of an article by displacement of an actuating part such as a pivotally supported arm or a linear plunger. The limit switches are designed to control the movement of a mechanical part. Limit switches are typically utilized in industrial control applications to automatically monitor and indicate whether the travel limits of a particular device have been exceeded. Level switch |[pic][pi| |c] | Various instruments have found use for applications requiring level sensing. Such instruments include float level switches, ultrasonic level switches and capacitance point level switches. Various devices have been proposed for indicating when liquid or other fluent material in a container or channel reaches a particular level. Liquid level sensors are used in a wide variety of applications to detect the levels of fluids within various forms of reservoirs. For example, such sensors are employed in the automotive industry to sense the level of oil in an oil pan or sump, or the level of transmission fluid. Liquid level sensors contain switches to indicate whether a sensed liquid is above or below a predetermined level. Switches responsive to fluid levels have utilized a variety of approaches for opening and closing an electrical circuit. Fluid level switch devices usually incorporate a float buoy for sensing the fluid level, the float buoy being operatively connected to a switch device. Temperature switch |[pic][pi| |c] | A temperature switch is a switch that is responsive to temperature changes. Temperature switches generally are provided with a temperature responsive element which will open or close a switch when a predetermined minimum pressure or temperature is sensed by the responsive element. For protection against thermal overload, semiconductor switches are provided with integrated temperature sensors. The temperature sensors acquire the temperature of the power switch and convert this into a temperature-dependent, analog signal which then can be interpreted in a circuit. Temperature sensitive switches, such as a thermostat, typically comprise a temperature sensor which is used to open or close electrical contacts at specified temperatures. A bimetal strip of dissimilar metals is used as the sensing element for temperature sensitive switches. Temperature sensitive switches are often used for thermal protection purposes. If a device gets too hot, the temperature sensitive switch opens the electrical circuit, thereby eliminating power to the circuit. For example, temperature responsive tip-switches are particularly useful in connection with electric heaters.

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