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
Hot oil pressure transmitter & display to read up to 5 bar at 300degC max - Pressure transmitter with an integral LED loop powered digital display for use with hot oil up to 300 deg. C (max.) over a pressure range of 0-5 bar gauge.
Electrophoretic painting tank level monitoring using flush ceramic transmitters - Using high-purity alumina diaphragms and PVDF connectors to provide reliable level monitoring in aggressive chemical environments found in car paint plants.
Featured negative gauge pressure measurement products
Negative 30 inHg vacuum gauge with 0-10V output - Dual-function vacuum gauge with digital display and 0-10V output for industrial process control and monitoring.
Waste toner dust extraction vacuum transmitter with 1000 mbar range - Intrinsically safe vacuum transmitter with ATEX approval for monitoring pressure in waste toner dust extraction systems. Features a 4-20mA output, G1/2" flush diaphragm process connection for reliable performance in hazardous dust environments.
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
400mm water level transmitter with 1mm accuracy - We are looking to measure liquid level to an accuracy of 1mm over a range of around 125mm.
2000 bar high pressure water pump 4-20mA pressure transducer - We are looking for a 4-20mA pressure transducer to measure pump pressure up to 2000 bar.
Related Help Guides
- Measuring vacuum with negative gauge or absolute ranges
- Measuring liquid level in a sealed tank with a hydrostatic pressure sensor
- What is the difference between gauge and absolute pressure measurement
- Measuring vacuum as a negative gauge pressure using a dp sensor
- 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
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