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
Viscous machine tool coolant level measurement with flush diaphragm sensor - Using a flush ceramic diaphragm to prevent clogging in viscous machine tool coolant tanks, ensuring reliable level measurement for oil and water emulsions containing swarf.
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.
Featured negative gauge pressure measurement products
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.
-760mmHg to +20 kg/cm² pressure transmitter with HART coms - Compound range transmitter for sensing pressure from -760 mm of mercury vacuum to 20 kilograms per sq cm positive pressure with HART communication.
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
20,000 psi g digital pressure gauge with 4 to 20 mA output - 4-20 milliamp loop powered high range pressure gauge for measuring 0 to 20,000 psi gauge.
UPS-HSR USB Pressure Sensor with High Sample Rate Logging - USB ready digital pressure sensor for recording pressures with a high speed sample rate of up to 1 kHz to a computer.
Related Help Guides
- 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 liquid level in a sealed tank with a hydrostatic pressure sensor
- Measuring vacuum as a negative gauge pressure using a dp sensor
- 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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