...
The majority of pressure sensors do not measure the pressure directly. The sensor consists Being a composite sensor, it consists of a sensing element that takes a primary reading (most commonly deformation followed by displacement, force or strain) and translates it to another non-electric physical quantity. Another sensor then translates this into an electrical signal that represents the output of the pressure sensor.
- A change in pressure causes the diaphragm to deflect, a corresponding change in resistance is induced on the strain gauge.
- This This changes can be measured by DAQ system.
- A metal is strongly bonded in the nearby surface where the strain is being measured.
- Bonded foils have quick 1000 Hz response times to changes in pressure as well as their large operating temperature.
...
In Figure 2A the applied pressure causes deformation of the sensing element (for example diaphragm), which is connected to a strain gauge that exhibits a change in resistance when mechanically strained. The value for pressure is then obtained by reading the variation of the output voltage which is proportional to the change in resistance of the strain gauge.
SimilarySimilarly, in Figure 2B a wiper (moveable electrical contact) is mechanically linked to the diaphragm and the applied pressure controls the wiper's position. This affects on the length of the wire (representing the resistance) between the wiper and the end of a potentiometer (variable resistance). The measurement for pressure is then obtained from the output voltage determined by that reflects the resistance value.
Pressure from capacitance variation
...
Pressure from inductance variation
The magnetic properties of the sensing element create a variation of the reluctance of the magnetic circuit which displaces the circuit's core. The direction and amplitude of the displacement are sensed by a diaphragm and translated into a signal, consecutively converted to electrical signal for the pressure.
In magnetic circuits we talk about reluctance instead of resistance. A change in distance between two magnetic devices causes a change in reluctance. In this type of sensor, the pressure acts on a part of the magnetic circuit (movable core) and changes the reluctance between the coils. The amplitude of the displacement is proportional to the output voltage which is used to calculate the applied pressure.
Pressure from piezoelectric effect
These types of sensors are used for dynamic pressure measurements. The change in stress of the diaphragm creates a strain and when a piezoelectric is used There are about 40 crystalline materials that generate electric charge when strained. Using such piezoelectrics as a sensing element, this strain the strain produced from a stress on the diaphragm is converted to electric charge . which is proportional to the pressure.
Pressure from oscillation
These sensors use a vibrating element which frequency of vibration depends on the force applied to it. This element is made from ferromagnetic material and induces voltage supplied by a detection coil, consecutively amplified and passed to an excitation coil. This voltage reflects the frequency of vibrations which follow a mathematical model to derive the pressure. The sensing element can be the vibrating element itself or connected to it.
Pressure from light intensity variation
The displacement of the sensing element (vane) gives a variation in light intensity . Using a photodiode that senses the change, it can relate that to the change in the force exerted on the sensing element.
Pressure from heating variation
The temperature of the sensing element varies in accordance to the surrounding pressure. The pressure measurement corresponds to that change in temperature.
between the source LED and the measuring LED. The diaphragm connected to the vane is moved by pressure, and therefore, the amount of infrared light received changes. This change in light intensity corresponds to the pressure applied.
Pressure from ion variation
The electrical current through pressure of a gas is related to the number of ions that provide it. The number of gas molecules is the same as the number of ions created in the gas by the impact of electrons. Therefore, the amount of electrical current reflects the molecule count, which then is used to calculate the pressure in accordance to the gas law. can be derived from measuring the ion current flow. Electrical current is supplied and when the electrons entering the gauge hit the gas molecules, they form positive ions causing ion current flow. The amount of that ion current is related to the gas density which is proportional to its pressure.
Data reliability
All pressure sensors are intrusive. Therefore, an incorrect installation can disturb the measurand or compromise the reliability of the system.
Range
...
Different pressure sensors have optimal working ranges. The process defines the operating range and the pressure sensor must be able to behave stable within that range. The range can vary from nPa for ionisation to GPa for strain gauges.
Accuracy
Signal Characteristics
Linearisation
Calibration
Noise
...
Sensitivity
The sensitivity of pressure sensors varies greatly between different types. Sensors based on strain gauge, ionisation, induction principles are very sensitive. Some ionisation pressure sensors can detect changes of 0.1 nPa. Potentiometric sensors have relatively low sensitivity.
Accuracy
The accuracy of a pressure sensor depends on the signal chain. It is the cumulative errors of each link of the chain. Typically ±0.1%. The most accurate pressure sensors are based on oscillation. Optical types have low accuracy.
Drift
All pressure sensor are subjected to drift over time. This is mainly because they undergo expansion and contraction when pressure is applied. The magnitude of drift depends on the usage (how frequently the pressure changes and to what extend) and the mechanical and thermal stability of the materials it is made of.
Applications
Pressure sensors are widely applied in energy generation industry where a constant monitoring and control of pressures is crucial for the operation of the power plants. Another application is in robotics where a pressure measurement is required in controls or as a substitute for touch. The proper operation of machines can be related to data from pressures of compressed air, gas, vapor, oil or other fluids.
...
- Ripka, P. and Tipek, A., 2007. Modern sensors handbook. 1st ed. Newport Beach, CA: ISTE USA.
- Huddleston, C., 2007. Intelligent sensor design using the microchip dsPIC. 1st ed. Amsterdam: Elsevier/Newnes.
- Engineers Garage. Available from: Engineersgarage.com, (2014). Pressure Sensors: Working Principle & Types of Pressure Sensor - EngineersGarage. [online] Available at: http://www.engineersgarage.com/articles/pressure-sensors-types-working [Accessed 30 April. 2014].
- Futek.com, (2014). Pressure Sensor selection. [online] Available at: http://www.futek.com/pressure_sensor_selection.aspx [Accessed 30 April. 2014].
- Controls.engin.umich.edu, (2014). PressureSensors - ControlsWiki. [online] Available at: https://controls.engin.umich.edu/wiki/index.php/PressureSensors [Accessed 30 April. 2014].