Some electronic sensors use other properties, such as density, ionization or thermal conductivity, to infer the pressure of a gas rather than measuring it directly.
A resonant sensor uses changes in resonant frequency (the frequency at which a gas vibrates most readily) to measure changes in gas density caused by pressure. The sensing element can be made from vibrating wire, a vibrating cylinder, quartz or silicon. Ionization sensors measure gas pressure by monitoring the flow of charged gas particles (ions), as it varies as a result of density changes.
Thermal sensors use changes in the thermal conductivity of a gas (how readily it conducts heat) to measure pressure.
In recent years, wireless pressure sensors have been introduced. These advanced sensors can be controlled remotely, which allows them to be used for applications where wired connections wouldn’t be possible. They typically offer more customization and control options than standard sensors, and some allow settings such as high and low limits to be altered while the unit is in operation.
Gas pressure sensors are transducers: they generate an electrical signal in proportion to the pressure they measure. This allows pressure to be monitored by microprocessors, programmable controllers, computers and other electronic devices connected to the sensor.
The sensor is based around a diaphragm made from monocrystalline silicon, polysilicon thin film, bonded metal foil, thick film or sputtered thin film.
The diaphragm acts as a semiconductor distortion gauge: when gas presses on it, it is bent out of shape, which distorts the crystalline structure of the material. This, in turn, changes the electrical resistance of the diaphragm, allowing the sensor to reflect changes in pressure in the form of a change in current (see diagram below).
Options and specification
A wide range of gas pressure sensors is available. They vary in terms of application suitability, cost, technology used, physical dimensions, fittings, process connectors and manufacturing materials used.
Gas pressure sensors normally have a working range defined in kilopascal (kPa), atmospheres (atm) or millimetres of mercury (Hg). They’ll also have an accuracy rating. For example, a sensor might have a working range of 0–210kPa, with accuracy of ±4kPa.
They may come with a stated response time, which reflects how long it takes them to provide a pressure reading – for example, 10ms. And they typically have a temperature range of operation, since the sensitivity of a pressure gauge can be affected by temperature.
Basic gas pressure sensors can only be used to measure the pressure of gases that are noncorrosive or non-flammable. For more information on measuring the pressure of corrosive gases, see our article on pressure sensors for corrosive media.