A pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical. Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers and manometers, among other names. Pressure sensors can vary drastically in technology, design, performance, application suitability and cost. A conservative estimate would be that there may be over 50 technologies and at least 300 companies making pressure sensors worldwide.
A pressure switch is a form of switch that closes an electrical contact when a certain set pressure has been reached on its input. The switch may be designed to make contact either on pressure rise or on pressure fall. A pressure switch for sensing fluid pressure contains a capsule, bellows, Bourdon tube, diaphragm or piston element that deforms or displaces proportionally to the applied pressure. The resulting motion is applied, either directly or through amplifying levers, to a set of switch contacts. Since pressure may be changing slowly and contacts should operate quickly, some kind of over-center mechanism such as a miniature snap-action switch is used to ensure quick operation of the contacts. One sensitive type of pressure switch uses mercury switches mounted on a Bourdon tube; the shifting weight of the mercury provides a useful over-center characteristic.
Pressure gauges, alternatively spelled as pressure gages, are instruments used to measure and display the pressure of a gas or liquid inside a closed system or vessel. They are capable of working with various liquids and gases.
To accommodate their many different applications, manufacturers make many different types of pressure gauges. Some are designed to measure specific substances or conditions. Examples of these include: water pressure gauges, air pressure gauges, oil pressure gauges, temperature gauges, gas pressure gauges, fuel pressure gauges, differential pressure gauges, and vacuum pressure gauges. Some of the uses of these gauges are more obvious than others. Water pressure gauges, of course, monitor the pressure of any water-based system.
Pressure transducers are devices that convert any physical force being exerted on them into electrical energy. In the simplest and most general definition, a transducer is any device that converts energy from one form to another. Pressure transducers take energy gained from pressure and convert that energy into electricity.
Transducers are key components in pressure sensors (also called pressure transmitters), and though the terms are frequently used interchangeably, a pressure transducer is technically just one part of a pressure sensor.
Level switches, also sometimes called level control switches, are measuring utilities that indicate material levels in storage enclosures or transmission equipment; in some cases they can be used both for level measurement and level control.
A level switch indicates these levels by means of an electrical switching action. Some of these devices could also be classified as level sensors or level indicators; those terms are restricted to systems that measure levels but do not control them.
A pressure switch is a device that senses changes in fluid pressure and responds in a specified way. An actuated pressure switch makes or disrupts electrical contact in order to either trigger an alarm or switch something on or off.
Switches are programmed to activate at certain pressure points, and may be designed to make contact either on pressure rise or on pressure fall.