You may not be aware but nearly every pressure measurement device you are using has a positive or negative gauge reference. It is so ubiquitous, that a gauge reference is often assumed and considered the default reference, neither mentioned in specification requirements or on manufacturers data sheets.
Although fundamentally pressure is defined and measured relative to a perfect vacuum in most scientific textbooks, it is impractical in the majority of industrial applications to measure pressure relative to an environment that does not exist naturally anywhere on terra firma. Instead most industrial equipment is located in an environment surrounded by air. To create movement of components on a machine, or to transfer a gas or fluid from one part of a process to another, a pressure has to be applied which is either greater or less than the surrounding ambient air pressure.
Local air pressure is the natural base pressure for all pressurised systems, before they are sealed and isolated from other components. This base pressure has no defined pressure value, and since local air pressure varies constantly, it is necessary to provide a way to track the gauge reference changes, to ensure a pressure reading is measured relative to the base pressure at all times.
The easiest and most practical way to continuously track a gauge reference is to provide a way to vent the reverse side of a pressure sensing device to the surrounding ambient air pressure. This will ensure that any change in the atmospheric pressure during measurement is compensated instantaneously.
Positive gauge pressure is any pressure that is measured above the current atmospheric pressure.
Negative gauge pressure is any pressure that is measured which is below the current atmospheric pressure.
Featured positive gauge pressure measurement products
Diesel exhaust fluid (DEF) level sensor for fleet management storage tanks - Monitor adblue® levels in storage tanks with the lmp307 sensor. Stainless steel construction, fkm seals, and 4-20ma output for seamless integration.
Irrigation water channel and storage dam SDI-12 submersible level sensor with 10m range - Submersible level sensor with SDI-12 interface for irrigation water channels and storage dams. 0 to 10m range, stainless steel 316L housing, Viton seals, and PUR cable. Ideal for agricultural water monitoring and telemetry systems.
Featured negative gauge pressure measurement products
30 inHg relative vacuum range digital display vacuum pressure gauge and logger - Battery-powered, pipe-mounted vacuum gauge with 0 to -30 inHg range, 0.1% accuracy, and USB data logging for industrial and research applications.
ATEX approved negative 10 mbar vacuum pressure transmitter - ATEX certified intrinsically safe pressure transmitter for measuring from 0 to minus 10 millibar gauge vacuum pressure.
If positive or negative is not mentioned when specifying a gauge reference pressure instrument, it is safe to assume that it is a positive gauge range, since the majority of applications require a positive pressure range. A negative gauge pressure range is normally identified in requirements by the way the pressure range is described, such as minus 2 psi or negative 1 bar gauge range.
You will also see something like 10 psi vacuum ranges or vac for short, but this can lead to confusion, since a vacuum range could be defined as an absolute or a gauge reference range, both requiring different types of measurement instrument. If a g, gauge, negative or minus is mentioned as part of the vacuum range description then it is reasonable to assume it is a negative gauge range and not an absolute one.
Featured gauge pressure measurement products
Diesel fuel oil tank level sensor with 200 mbar range for internal installation - Fuel oil pressure sensor with a 4-20mA current output and a submersible electrical connection for lowering inside a Diesel fuel storage tank to measure hydrostatic level of fuel oil up to 200 millbar.
Storm surge protected low range submersible river level transmitter - This submersible level transmitter offers accurate low range water level monitoring with high overpressure resistance for storm surge protection in rivers
Related Help Guides
- Measuring liquid level in a sealed tank with a hydrostatic pressure sensor
- Measuring vacuum as a negative gauge pressure using a dp sensor
- Measuring vacuum with negative gauge or absolute ranges
- What is the difference between gauge and absolute pressure measurement
- Can you measure vacuum using a gauge pressure range
- Measuring gauge pressure using a dp sensor
- What does the suffix a, abs, d, dp and diff, g, rel and sg mean after the pressure units in a pressure range?
Related Technical Terms
- Gauge Reference Pressure
- Negative Gauge Pressure
- Reference Pressure
- SG – Sealed Gauge
- Vented Cable
- Vented Gauge