Pressure Sensor and Types of pressure measurements

A pressure sensor is a device or device that can sense pressure signals and convert the pressure signals into usable output electrical signals according to certain rules.A pressure sensor usually consists of a pressure sensitive element and a signal processing unit.According to the different types of test pressure, pressure sensors can be divided into gauge pressure sensors, differential pressure sensors and absolute pressure sensors.Pressure sensors are the most commonly used sensors in industrial practice.Widely used in various industrial automation environments,involving water conservancy and hydropower,railway transportation,intelligent buildings,production automation,aerospace,military industry,petrochemical,oil wells,electric power,ships,machine tools,pipelines and many other industries.A pressure sensor is a device that measures the pressure of a gas or liquid.Pressure represents the force required to stop a fluid from expanding,usually expressed in force per unit area.A pressure sensor typically acts as a transducer;it generates a signal based on the applied pressure.For purposes herein, such signals are electrical signals.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,velocity,water level and altitude.Pressure sensors can also be called pressure sensors,pressure transmitters,pressure transducers,pressure indicators, pressure gauges,and manometers,among other names.Pressure sensors can vary widely in technology,design,performance,application suitability,and cost.At a conservative estimate,there are probably more than 50 technologies and at least 300 companies making pressure sensors worldwide.There is also a class of pressure sensors designed to measure in dynamic mode to capture very high-speed pressure changes.Example applications for such sensors include measuring combustion pressure in engine cylinders or gas turbines.These sensors are usually made of piezoelectric materials such as quartz.Some pressure sensors are pressure switches that turn on or off at a specific pressure. For example,a water pump can be controlled by a pressure switch so that it starts when the system discharges water, reducing the pressure in the reservoir.

Types of pressure measurements 

Pressure sensors can be classified according to the pressure range they measure, the temperature range they operate in and most importantly the type of pressure they measure.Pressure sensors have different names depending on what they are used for, but the same technology may be used by different names.

Absolute pressure sensor

This sensor measures pressure relative to a perfect vacuum.Absolute pressure sensors are used in applications requiring a constant reference such as high performance industrial applications such as monitoring vacuum pumps,liquid pressure measurement,industrial packaging,industrial process control and aerospace inspection.

Gauge pressure sensor

This sensor measures pressure relative to atmospheric pressure.A tire gauge is an example of gauge pressure measurement;when it indicates zero,it is measuring the same pressure as the ambient pressure.Most sensors for measuring up to 50 bar are manufactured in this way,otherwise atmospheric pressure fluctuations (weather) would be reflected as errors in the measurement results.

Vacuum pressure sensor

This term can be confusing.It can be used to describe sensors that measure pressure below atmospheric pressure, showing the difference between low pressure and atmospheric pressure, but it can also be used to describe sensors that measure absolute pressure relative to a vacuum.

Differential pressure sensor

This sensor measures the difference between two pressures, one attached to each side of the sensor.Differential pressure sensors are used to measure many properties such as the pressure drop across an oil filter or air filter, liquid level (by comparing the pressure above and below the liquid) or flow rate (by measuring the pressure change in a restriction).Technically, most pressure sensors are actually differential pressure sensors; for example, a gauge pressure sensor is just a differential pressure sensor with one side open to the ambient atmosphere.

Sealed pressure sensor

This sensor is similar to a gauge pressure sensor, except that it measures pressure relative to some fixed pressure rather than ambient atmospheric pressure (which varies depending on location and weather).

Pressure-sensing technology

There are two basic categories of analog pressure sensors,Force Harvester Types These types of electronic pressure transducers typically use a force harvester (such as a diaphragm, piston, Bourdon tube, or bellows) to measure the strain (or deflection) due to the application of a force on an area (pressure).

Piezoresistive strain gauge

Using the piezoresistive effect of bonded or formed strain gauges to detect strain induced by applied pressure,resistance increases as pressure deforms the material. Common technology types are silicon (single crystal),polysilicon thin film, bonded metal foil, thick film, silicon on sapphire,and sputtered thin film. Typically,the strain gages are connected to form a Wheatstone bridge circuit to maximize the output of the sensor and reduce the sensitivity to error.This is the most commonly used sensing technology for general pressure measurement.

Capacitive

A diaphragm and a pressure chamber are used to create a variable capacitor to detect the strain due to applied pressure,with the capacitance decreasing as the pressure deforms the diaphragm.Common technologies use metal,ceramic and silicon diaphragms.Capacitive pressure sensors are being integrated into CMOS technology and the possibility of using thin 2D materials.

Electromagnetic

Diaphragm displacement measurement via changes in inductance (magnetoresistive),LVDT, Hall effect or eddy current principles.

Piezoelectric

The piezoelectric effect in certain materials such as quartz is used to measure the strain on the sensing mechanism due to pressure.This technique is commonly used to measure high dynamic pressures.Since the basic principle is dynamic,piezoelectric sensors cannot measure static pressure.

Strain-Gauge

Strain gauge based pressure sensors also use pressure sensitive elements with metal strain gauges glued on or thin film gauges applied by sputtering.The measuring element can be a diaphragm or canned metal foil measuring body.The biggest advantage of this one-piece tank design is increased rigidity and the ability to measure maximum pressures up to 15,000 bar.The electrical connection is usually done with a Wheatstone bridge,which amplifies the signal well and obtains precise and constant measurements.

Optical

Techniques include using physical changes in optical fibers to detect strain due to applied pressure.A common example of this type is the use of Fiber Bragg Gratings.This technique is used in challenging applications where measurements may be at great distances,at high temperatures,or may benefit from inherent EMI immunity.Another similar technique utilizes a multilayer construction of elastic films that can change the reflected wavelength in response to applied pressure (strain).

Potentiometric

Using the movement of the wiper along the resistance mechanism to detect the strain induced by the applied pressure.

 Force balancing

Force Balancing Fused Silica Bourdon Tubes use a helical Bourdon tube to apply a force on a rotating armature containing a mirror,a beam of light reflected from the mirror senses the angular displacement,a current is applied to the electromagnet on the armature to remove the force from the tube and the angular displacement is made zero and the current applied to the coil is used as the measured value.These sensors are accurate to around 1PPM of full scale due to the extremely stable and repeatable mechanical and thermal properties of fused silica and the force balance that eliminates most nonlinear effects.Since the handmade extremely fine fused silica structures require specialized skills to construct these sensors are usually limited to scientific and calibration purposes. Non-force-balanced sensors have lower accuracy and cannot read angular displacement with the same accuracy as force-balanced measurements,although these sensors are no longer used due to their larger size and easier construction.

Other types

• Resonant

• Thermal

• Ionization