Pressure

Pressure sensor

Ebora supplies among others:

• Pressure gauges
• Pipe spring pressure gauges
• Hair spring pressure gauges
• Vacuum pressure gauge

• Pressure measurement:
• Pressure gauge
• Pressure sensors
• Pressure switches
• Differential pressure gauge
• Hygienic pressure gauge
• High pressure gauge
• etc.

A pressure sensor is a measuring instrument for measuring the pressure of gases or liquids. Pressure is an expression of the force required to stop the expansion of a liquid and is usually expressed in force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the applied pressure.

Standard output signals for pressure sensors are:

• 4..20 mA
• 4..20 mA HART
• 0..10 V

Pressure sensors are used for control and monitoring in thousands of applications. Pressure sensors can also be used to indirectly measure other variables, such as liquid/gas flow, speed, water level and altitude. Pressure sensors can also be called pressure transducers, pressure transmitters, pressure sensors, pressure transmitters, pressure gauges, pressure gauges, piezometers and pressure gauges, among other names.

Pressure sensors can vary drastically in technology, design, performance, application possibilities and costs.

Common types of pressure sensors are:

Absolute pressure sensor

This sensor measures the pressure compared to a perfect vacuum.

Relative pressure sensor

This sensor measures the pressure relative to the atmospheric pressure. A tyre pressure gauge is an example of measuring overpressure; when it indicates zero, the pressure it measures is the same as the ambient pressure.

Vacuum pressure sensor

This term can cause confusion. It can be used to describe a sensor that measures a pressure under atmospheric pressure that represents the difference between that low pressure and atmospheric pressure, but it can also be used to describe a sensor that measures absolute pressure compared to a vacuum.

Differential pressure sensor

This sensor measures the difference between two pressures, one of which is connected on both sides of the sensor. Differential pressure sensors are used to measure many properties, such as pressure losses over oil filters or air filters, fluid levels (by comparing the pressure above and below the fluid) or flow rates (by measuring the pressure change over a narrowing). Technically, most pressure sensors are true differential pressure sensors; an overpressure sensor, for example, is only a differential pressure sensor where one side is open to the ambient atmosphere.

Closed pressure sensor

This sensor is similar to an overpressure sensor, except that it measures the pressure against a certain fixed pressure instead of the atmospheric ambient pressure (which varies depending on location and weather).

Most common principles for pressure sensors:

There are two basic categories of analogue pressure sensors,

Force sensors: These types of electronic pressure sensors typically use a force (such as a diaphragm, piston, bourdon tube or bellows) to measure the tension (or deflection) due to the force applied over an area (pressure).

Piezoresistive pressure sensors

Uses the piezoresistive effect of bound or formed strain gauges to detect strain due to the pressure applied, with resistance increasing as pressure deforms the material. Common technologies include Silicon (Monocrystalline), Polysilicon Thin Film, Bonded Metal Film, Thick Film, Silicon-on-Sapphire and Sputtered Thin Film. Generally, the strain gauges are connected to form a Wheatstone bridge circuit to maximize sensor output and reduce susceptibility to errors. This is the most widely used sensor technology for general pressure measurements.

Capacitive pressure sensors

Uses a diaphragm and pressure cavity to create a variable capacitor for detecting voltage due to the applied pressure, with the capacity decreasing as the pressure deforms the diaphragm. Common technologies use metals, ceramic and silicon membranes.

Electromagnetic pressure sensors

Measures the displacement of an aperture by means of changes in inductance, LVDT, Hall Effect, or by eddy current principle.

Piezoelectric pressure sensors

Uses the piezoelectric effect in certain materials such as quartz to measure the pressure load on the detection mechanism. This technology is often used to measure highly dynamic pressures. Because the basic principle is dynamic, no static pressure can be measured with piezoelectric sensors.

Strain gauge pressure sensors

The strain gauge pressure sensors also use a pressure-sensitive element on which metal strain gauges are glued or thin film gauges are applied by means of sputtering. This measuring element can be either a membrane or metal foil gauges can also be used in tinned gauges. The main advantages of this monolithic tin type are improved stiffness and the possibility to measure the highest pressure up to 15.000 bar. The electrical connection is normally made via a Wheatstone bridge, which allows a good amplification of the signal and accurate and constant measurement results.

Some pressure sensors are pressure switches that switch on or off at a certain pressure. For example, a water pump can be controlled by a pressure switch, so that it starts when water is released from the system, thus reducing the pressure in a reservoir.