A Complete Guide to Pressure Sensors

Pressure sensors are measurement tools for detecting, monitoring, reading and displaying changes in applied pressure from a contained volume of liquid or gas. They can also be used with uncontained volumes, such as atmospheric pressure. There are various types of pressure sensors available for performing in specific roles, conditions and applications.

In this guide to pressure sensors, we will provide a clear definition of pressure sensors and a basic explanation of how they work. We will also look at several of the different types of pressure sensors for sale online in the UK, describing how and why they might be used.

Pressure sensors are widely used in various demanding applications across a wide range of industries and sectors. Different types can incorporate many variations in core technology, features and performance levels.

Pneumatic pressure sensors measure changes in air or gas pressure, while hydraulic pressure sensors measure changes in water or fluid pressure. Different technologies for constructing these devices can result in configurations such as piezoresistive pressure sensors, capacitive pressure sensors, fibre optic pressure sensors, and strain-gauge pressure sensors.

Between them, they cover a broad array of industrial or scientific pressure measuring techniques and applications. Knowing how to use a pressure sensor will depend entirely on the type and the role you want it to perform, but some common examples of industrial pressure sensor use might include:

• Checking the applied pressure (or min/max pressure measurements) of various gases and liquids held in sealed tanks, vessels and systems. Entire tyre pressure monitoring systems, such as found in a vehicle's tyre pressure gauge, are a good everyday example of electronic pressure sensors in action
• Detecting flow rate and direction by tracking pressure changes between two or more separate locations
• Interpreting shifts in atmospheric pressure (i.e. barometric pressure) for environmental or navigational purposes
• Monitoring volumes and liquid levels via pressure exerted downward on a sensor

Before we take a closer look at the various types of pressure sensors available, we should make a quick note of the key definitions and differences between sensors, transducers, and transmitters.

Any pressure sensor device relies on changes in pressure causing a physical reaction in the sensing element. This change cannot be fed directly through to an attached circuit until it has been suitably translated and conditioned into a usable electronic signal.

The reason we need to differentiate between pressure sensors, pressure transducers and pressure transmitters is that they all incorporate a pressure sensing element, but each translates and conditions the output signal from that element in slightly different ways. Despite this, casual use of the generic term pressure sensor may refer to any of these three device types.

Pressure Sensors

A true pressure sensor works on the principle whereby a physical reaction in the sensor module produces an output voltage. Further signal conditioning - such as calibration, amplification, and temperature compensation - must be handled separately before readings are considered reliable and stable.

Pressure Transducers

The question ‘what is a pressure transducer?’ often follows from any explanation of a pressure sensor, which is understandable. Like pressure sensors, pressure transducers also produce an output voltage because of a physical reaction in the sensing element. The key difference is that some degree of signal conditioning is also handled by the transducer, allowing them to be transmitted a greater distance from the source.

Pressure Transmitters

A pressure transmitter works much like a transducer, except rather than a voltage reading, it will output a current signal across a low-impedance load (often somewhere in the 4-20mA standard industrial range).

What is Pressure?

Pressure is defined as the force applied to the surface of an object or medium, per unit of area across which the force is being exerted. In mathematical terms, it is a function of the formula p = F/A, where p is pressure,** F** is (perpendicular) normal force, and A is the surface contact area.

What are the Main Units of Pressure?

Since 1971, the main SI unit for pressure is the pascal, usually written as Pa. Before this, it was standard for pressure to be given in newtons per metre squared. One pascal is equivalent to one newton per square metre (N/m2). Various other non-SI ways of indicating pressure are widely used across a diverse range of applications, with common variants including bar pressure and pounds per square inch (PSI).

How Do You Test a Pressure Sensor?

There are various ways to test different functions of a pressure sensor, some of which can be quite in-depth and demanding from a technical standpoint. You will generally require access to several other tools and devices, including a pressure fluke, multifunction voltage meter with suitable probes, power supply, breadboard, and wires or jumper cables.

The core approach to any comprehensive pressure sensor test should usually involve checking for the following four key things:

• Basic function - ensuring the sensor outputs a voltage when it detects a pressure change
• Accuracy - ensuring the same sensor outputs the same reading in response to the same pressure change
• Consistency - ensuring multiple sensors all produce the identical outputs under identical conditions
• Resolution - checking that a sensor meets its minimum rated requirements for detecting very small changes in pressure