Pressure sensors help notify maintenance teams of risks before serious failures occur, allowing corrective action to take place. There are seven main types of pressure sensors: Aneroid barometer pressure sensors, manometer pressure sensors, bourdon tube pressure sensors, vacuum (Pirani) pressure sensors, sealed pressure sensors, piezoelectric pressure sensors, and strain gauge pressure sensors.
Pressure sensors are extremely useful devices that measure the physical pressure of gases or liquids via a sensor and output signal. Pressure is defined as the force required to stop a fluid from expanding, typically displayed as force per unit area.
Pressure sensors are used to control and monitor a wide range of everyday applications, including indirect measurements of gas/fluid flow, speed, altitude, and water levels.
Because of their wide range of uses in applications, they vary drastically in technology, design, performance, stability, and cost. This article will discuss the different types of pressure sensors, describe the working principles, and review which common applications utilize them.
There are several common terms often used interchangeably to describe pressure sensors. Those include pressure transducers, pressure transmitters, and pressure indicators, among others. Despite which term is used, they all produce an output signal and measure pressure.
Pressure is defined as the amount of force (exerted by a gas or liquid) applied to a unit of ‘area’. Pressure sensors allow more specialized maintenance strategies, and they can predict and prepare for risk failures because they work on real-time data.
Applications that have a pressure sensor installed mean that maintenance teams are alerted when necessary, allowing them to address the issue immediately. The most common type of pressure sensor used is a transducer (piezoelectric and strain gauge) as they are applied to applications to monitor flow, airspeed, level, pump systems, or altitude.
Pressure Sensor Terminology
Before we get into the different types of pressure sensors, there is some key terminology related to pressure sensors that you should know about.
Gauge Pressure: The measurement of pressure relative to ambient pressure
Absolute Pressure: The measurement relative to a pure vacuum of space – this is important when measuring altitude pressure changes
Differential Pressure: The pressure difference between two applied pressure values
Vacuum Pressure: The pressure measurement that is less than the surrounding atmospheric pressure
How Do Pressure Sensors Work?
All pressure sensors use the same basic working principle by measuring a physical change in pressure differences. Once the pressure sensor measures a physical change, the information is transmitted into an electrical signal, which is then displayed as usable data for the user to interpret.
The working principle of pressure sensors can be broken down into four steps:
The apparatus which allows expansions and contractions converts pressure into voltages or electrical signals
Once the pressure sensor produces an electrical signal, they are measured and recorded
The CMMS* receives an electrical signal from the pressure sensor in real-time
The CMMS alerts maintenance teams when the pressure is too high or too low – pressure ratings that are too high typically indicate rupturing risks and loss of pressure can indicate leakage
*CMMS stands for a computerized maintenance management system. It is software that centralizes assets, schedule maintenance, and helps optimize the utilization of physical equipment.
The Difference Between Transducers, Transmitters, And Sensors
The reason why it is important to differentiate between pressure sensors, pressure transducers, and pressure transmitters is that they are often used interchangeably, but each slightly differs.
A ‘true’ pressure sensor works on a physical reaction. The sensor module inside the pressure sensor produces an output voltage. Calibration, amplification, and temperature compensation must be addressed beforehand so that the results are reliable and stable.
Pressure transducers produce an output voltage like a pressure sensor, as they also have a physical reaction inside the sensing element of the sensor. However, pressure transducers can also handle signal conditioning, which allows them to be transmitted a greater distance.
These work very similarly to a pressure transducer, but instead of a voltage reading, pressure transmitters output a current signal across a low-impedance load.
Seven Types Of Pressure Sensors
Pressure sensors are designed and categorized according to the configuration they use to sense pressure changes.
The different types of pressure sensors are listed below:
#1: Aneroid Barometer Pressure Sensors
Aneroid barometer pressure sensors are purely mechanical devices to measure pressure. These types of pressure sensors are composed of a hollow, airtight metal casing with a flexible surface, resembling a capsule.
Atmospheric changes cause the capsule to compress and expand, causing it to change shape in response to the surrounding pressure. The level of deformation can be measured and coupled to a dial that translates the pressurized deformation to a corresponding pressure reading.
These sensors are compact and very durable, typically used to measure atmospheric pressure in aircraft and environmental applications. The only downfall to aneroid barometer pressure sensors is the mass of pressure sensing elements which usually limits the device’s response rate, therefore, making them less effective for dynamic pressure sensing applications.
#2: Manometer Pressure Sensors
Manometer pressure sensors are glass tube, fluid-type pressure sensors that follow a simple design structure, however, they have an accuracy greater than aneroid barometer pressure sensors, which is impressive as they were one of the earliest devices invented to measure pressure. The movement of the liquid-filled tube compares the pressure difference between the two surfaces.
The most common manometer sensor is U-shaped. Pressure is applied to one side of the glass tube, displacing the liquid inside, which causes a drop in the fluid level at one end of the tube and a rise at the other. The difference in height between the two ends of the tube indicates the pressure level, and a measurement is taken.
They are commonly used to calibrate equipment in laboratory applications. However, manometers have a fairly slow response rate and a limited range of pressures, therefore they are inadequate for dynamic pressure-sensing applications.
#3: Bourdon Tube Pressure Sensors
Bourdon tube pressure sensors function on the same principle as aneroid barometers, yet, they have a helical or C-shaped sensing element instead of a hollow, airtight metal capsule.
They are innovative mechanical measuring devices that use physical movements. One end of the tube is closed, while the other end is exposed to the surroundings being measured. As more pressure is applied to the sensor, the coil (elliptical cross-section) of the tube begins to straighten. The bourdon tube continues to straighten until the fluid pressure matches the tube’s elastic resistance. It is the physical motion of the coil that moves the pointer along a graduated dial to display the pressure readings.
Bourdon tubes are commonly used as gauge pressure sensors and differential sensors due to their simplicity and toughness. They also tend to be inexpensive, yet durable, providing high accuracy across high-pressure applications.
The disadvantage of using a bourdon tube pressure sensor is their susceptibility to shock and vibration because they are purely mechanical. Therefore, they are not recommended for use in low-pressure applications that require very precise measurements.
#4: Vacuum Pressure Sensors
The above pressure sensors generally work by measuring an applied force to a mechanical apparatus, however, when mechanical methods become complex and the pressure drops below atmospheric levels, pressure sensors that observe and measure the effects on the material are used. This is where vacuum pressure sensors come in.
A Pirani sensor (invented by Marcello Pirani in 1906) is the most common and well-known sensor used to measure low vacuum pressure ranges.
These types of pressure sensors measure the resistance of a heated sensor filament (typically made from thin tungsten, nickel, or platinum wire) inside the gauge chamber. As the gauge chamber becomes exposed to the surrounding vacuum pressure, gas molecules collide with the filament wire, and heat is transported from the sensor wire. The wire is connected to an electrical circuit from which, after calibration, the pressure reading is taken.
At low pressures, the temperature drops, resulting in low thermal conductivity. At high pressures, the high gas density results in high thermal conductivity.
#5: Sealed Pressure Sensors
Sealed pressure sensors are commonly used to measure atmospheric pressure at sea level on submersible vehicles to establish depth by measuring and comparing ambient pressure alongside available atmospheric pressure in the sealed device.
The chamber maintains the same air pressure since it was sealed, which becomes the permanent internal reference pressure of the pressure sensor.
#6: Piezoelectric Pressure Sensors
Piezoelectric sensors work by employing an electric charge as a response to physical changes to the material. The charge created from physical changes is directly proportional to the applied force. The piezoelectric pressure sensor measures and calibrates changes in the electrical charge, displaying a corresponding pressure measurement for the user to view.
These types of pressure sensors have high frequency and rapid response times, yet they are very small, making them a perfect choice of pressure sensor for applications that have space constraints. They are mainly used for measuring dynamic pressure, for example in engine combustion applications.
#7: Strain Gauge Pressure Sensors
As the name suggests, strain gauge pressure sensors use the proportional expansion or contraction in the spring’s dimensions to measure pressure.
When a force is applied, the spring element inside the strain gauge pressure sensor deforms. When pressure changes occur, the resistance fluctuates and voltage readings are recorded as electrical signals. These can then be converted to an equivalent pressure reading and displayed by the strain gauge sensor.
Strain gauge pressure sensors are used for long-term monitoring tasks such as measuring residual stress, torque, compression, tension, bending, and deflection of vehicles, ship hulls, dams, and oil drilling platforms.
Pressure Sensor Considerations
When deciding which type of pressure sensor will best suit your needs, you should consider the following points:
Sensor type – this is the primary consideration when selecting the right pressure sensor for your application needs
With the various types of pressure sensors available, they can be used in a wide range of applications from HVAC systems to general industrial uses.
In addition to the applications mentioned above, below are some examples of common uses of the different types of pressure sensors:
Pipeline hoses often operate at extreme pressures, for example, gas pipelines can operate anywhere from 200-1500 PSI (pound-force per square inch). Wire-braided hydraulic hoses also have very extreme working pressures (6000 PSI), therefore a pressure sensor ensures that they never exceed their limits.
Vacuum technology is used in industrial and scientific processes. An example of low to high-vacuum pressure systems includes composite molding production, flight instrument manufacturing, medical applications, and semiconductor processing. These all require vacuum pressure sensors that can work upwards of 10,000 PSI.
Environmental applications require pressure sensors to be used in emission testing, wind management applications, and pollution devices.
Manufacturing processes that involve hydraulic and pneumatic systems require pressure sensors to detect anomalies such as leaks, potential failure, or compression issues.
Automotive brake systems use pressure sensors to detect faults that could impact their function. Automobile engines need pressure sensors to prevent oil pressure levels from exceeding the recommended level of the operating engine.
In medical equipment like ventilators, pressure sensors are critical in measuring oxygen pressure and how much air is supplied to the patient. In hyperbaric chambers, pressure sensors monitor and control the internal pressure of the chamber during the treatment process. Pressure sensors are also used in spirometry equipment that measures a patient’s lung volume.
In HVAC systems, the condition of air filters is often measured by pressure sensors. If the air filter becomes clogged, the differential pressure increases and can be detected using the sensor. They are also useful to monitor the rate of airflow speed in radiators and air conditioning units.
In industrial applications, pressure sensors are also used to detect clogged filters, however, it does so by assessing the difference between the influent and effluent pressures inside the filter.
Pressure is the amount of force (exerted by a gas or liquid) applied to a unit of “area”.
Pressure sensors help notify maintenance teams of risks before serious failures occur, allowing corrective action to take place. There are seven types of pressure sensors to choose from, depending on what application you are working with, however, the most common type of pressure sensor used is a piezoelectric or strain gauge pressure sensor.
If you have any questions regarding pressure sensors or which pressure sensor will best suit your testing needs, do not hesitate to contact our world-class team at Atlas Scientific.
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