What is a pressure sensor?

       A pressure sensor is a type of transducer which measures pressure. Pressure sensors typically measure the pressure of liquids and gases. As a review, pressure means the force exerted per unit area and it has the typical unit of Newtons per square meter, Pounds per square inch and Millimeter of mercury or Torr.  When we talk about electrical or electronic pressure sensors, we mean sensors which convert pressure into an electrical quantity. Some pressure sensors convert pressure into voltage while others convert pressure to a change in resistance. Pressure sensors can indirectly measure other quantities like as fluid/gas flow, speed, water level, and altitude. Some other name of pressure sensors include piezometers, manometers, pressure indicator, pressure sender, pressure transmitter and pressure transducer. There are at least 50 technologies used in the manufacture of pressure sensors which results in pressure sensors with varying design, performance, application suitability and cost effectiveness.  There are pressure sensors that can measure very high speed changes in pressure, they are usually made up of piezoelectric materials like quartz and their typical application is the measurement of pressure inside a combustion engine. Pressure sensors that detect only the presence or absence pressure are known as pressure switches. These are found in traffic enforcer cameras.

Pressure sensor technologies

Force Collector Types – uses a mechanical force collector to measure strain or deflection. The force collector can be  a diaphragm, piston, bourdon tube, or bellows.

Piezoresistive Strain Gage – depends on the piezoresestive effect of crystals that are bonded on a casing to detect strain caused by applied pressure. These type of strain gages are connected in a Wheatstone bridge to enable a more accurate output. This technology is widely used for general purpose pressure measurement.  Pressure sensors that measure absolute, gauge, vacuum and differential pressure use this technology.

Capacitive Pressure sensors – uses a diaphragm or a plate which resembles a variable capacitor. The capacitance of the pressure sensor is dependent on the applied pressure. Capacitive pressure sensors use metal, silicon or ceramic diaphragms. It is widely used in the manufacture of low pressure absolute, differential and gauge pressure sensor.

Electromagnetic Pressure sensors – the displacement of a diaphragm caused by a pressure source can also measured by the use of a device which changes its inductance, LVDT and Hall effect sensors.

Piezoelectric Pressure sensors -  use the piezoelectric effect of crystals like quartz to measure the strain on the sensing mechanism. This is commonly used to manufacture pressure sensors with high dynamic pressure.

Optical Pressure sensors – they are dependent on the physical change on the fiber optic to detect strain caused by pressure. Pressure sensors of this type are used in applications that involve high temperature, exposed to high amounts of electromagnetic interference and highly remote places.

Potentiometric Pressure sensors – uses the wiper of a variable resistor to detect the strain coming from the applied pressure.

Pressure Sensor Applications

1. Tire pressure Sensor – tire pressure sensors are specially designed pressure sensors that are embedded inside the tire itself. It is composed of a microcontroller which processes the pressure data and transmits it via radio frequency. The data is received on dashboard receivers to alert the driver if the tire pressure is too low or if the tire is punctured.

2. Oil pressure sensor – oil pressure sensors are specifically designed to measure oil pressure. Electronic oil pressure sensors integrate a signal conditioning circuitry; it transmits pressure information on the dashboard of the car or on a control center.

3. Air pressure sensor – they are used to measure barometric air pressure or to measure altitude indirectly. Air pressure decreases as altitude increases, the decrease in pressure is proportional to the altitude.

Pressure Sensor Types

Pressure sensors are classified in terms of the pressure ranges that they can measure, temperature range, and the type of pressure they measure. When we speak of the pressure type, pressure sensors can be classified into the following categories.

Absolute pressure sensor - This pressure sensor measures the pressure relative to vacuum pressure which is 0 PSI .

Gauge pressure sensor - It measures pressure relative to normal atmospheric pressure on one location. Gauge pressure sensors are typically used in measuring the pressure of tires.

Vacuum pressure sensor - This pressure sensor is used to measure pressure that is less than the atmospheric pressure at a specific location.

Differential pressure sensor - This pressure sensor measures the difference of pressure between two or more inlet ports of pressure. Differential pressure is also used in measuring the flow or level in pressurized containers.

Sealed pressure sensor - This pressure sensor is the same as the gauge pressure sensor except that it is calibrated by manufacturers to measure pressure that is relative to the air pressure at sea level which is 14.7 PSI