Pressure Measurement Glossary

Look up a word or phrase to find the associated definition and meaning from this list of pressure measurement terms indexed in alphabetical order.


Glossary Index

A | B | C | D | E | F | G | H | I

J | K | L | M | N | O | P | Q | R

S | T | U | V | W | X | Y | Z

Numeric



A

a
- see absolute pressure.
Abs
- see absolute pressure.
Absolute Pressure (Abs, a)
- particular type of pressure measurement which is always referred to a perfect vacuum.
Accuracy
- defines how much a measurement of pressure deviates from the actual true pressure value.
Ambient Air Pressure
- see barometric pressure.
at
- see technical atmosphere.
atm
- see standard atmosphere.
Atmospheric Pressure
- see barometric pressure.

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B

Barometric Pressure
- total outside air pressure measured with reference to a perfect vacuum. The pressure varies depending on geographical location, altitude and local weather conditions. For weather reporting purposes the barometric pressure is normally adjusted to a sea level value so that all locations can be compared independent of the altitude at each location
bar
- widely used metric unit of measure for pressure and 1 bar converts precisely to 100,000 Pascals.
bara
- means bar absolute.
bard
- means bar differential.
barg
- means bar gauge.
Best Straight Line (BSL)
- mathematically derived straight line which runs through the middle of a set of pressure readings in such a way to achieve the smallest error across all the results.
Best Straight Line Accuracy
- defines the limit that any pressure measurement reading will deviate from the Best Straight Line.
Bonded Foil Strain Gauges (BFSG)
- metal based foil elements that are incorporated into a flexible electrically insulating material which can then be bonded to a diaphragm with adhesives. As pressure is applied to the diaphragm the strain gauge will deform and its resistance will change.
Bonded Seal
- metal washer with an elastomer seal bonded to its inside diameter, which is used to provide a pressure seal when placed between two flat surfaces that are screwed together using a male and female parallel thread.
BFSG
- see bonded foil strain gauge.
BSL
- see best straight line.
Burst Pressure
- is a design safety limit which should not be exceeded. If this pressure is exceeded it may lead to mechanical breach and permanent loss of pressure containment.
Bourdon Tube
- is a flattened length of thin hollow metal tubing which is formed into a C shape.

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C

Cardinal Points
- markings around the outside of an analogue pressure gauge dial which define the increments of pressure
Centimetres of H2O (cmH2O), Centimetres of Water Gauge (cmWG) or Centimetres of Water Column (cmWC)
- manometric unit used to relate a pressure reading to the height of fresh water at a temperature of 4 degC. 1 Centimeter of Water Gauge equals 98.0665 Pascals.
Centimetres of Mercury (cmHg)
- small pressure unit which represents the pressure pushing down due to gravity of any volume of liquid mercury which is 1cm high. 1 Centimeter of Mercury at zero degrees Celsius equals 1333.22 Pascals.
Ceramic Pressure Sensors
- use sensing diaphragms made from Alumina (Al2O3) with either a screen printed thick film strain gauge circuit or a variable capacitance cell. Ceramic diaphragms are very inert and provide a high level of protection from aggressive chemicals.
Chemraz®
- see perfluoroelastomer.
cmAq
- see centimetres of water.
cmH2O
- see centimetres of water.
cmHg
- see centimetres of mercury.
cmWC
- see centimetres of water column.
cmWG
- see centimetres of water gauge.
Compensated Temperature Range
- limits that temperature errors have been tested over and are not necessarily related to the operating temperature range. A pressure measurement device may continue to function outside the compensated temperature range but the accuracy of any measurement is not defined.
Compound Pressure Ranges
- combination of positive and negative pressure ranges into one pressure measurement device.

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D

Deadband
- region of pressure where a change in pressure produces no change in measurement output or control signal.
Dead Weight Tester
- pressure calibration instrument which uses metal weights and a piston/cylinder assembly to generate pressure setpoints to a high accuracy over a wide range of pneumatic or hydraulic pressures.
Delta P
- see delta pressure and differential pressure.
Delta Pressure (Delta P)
- net change in pressure over a period of time or the difference in pressure between two different points (also see differential pressure).
Diff
- see differential pressure.
Differential Pressure (DP, Diff, Delta P)
- difference in pressure between two separate points.
Digital Compensation
- process of collecting many measured points at different pressures and temperatures and using this data to correct the output of a pressure transducer so that the pressure accuracy and thermal errors can be improved beyond what is practically achieved with analogue compensation.
DP
- see differential pressure.
Dowty® Bonded Seal
- see bonded seal.
DP Cell
- type of differential pressure sensor which consists of two oil filled chambers separated by a single sensing element.
Drift
- see long term drift.
Dry Cell
- pressure sensing technology which excludes any fluid filled components.
Dry/Dry
- differential pressure measurement device which is compatible with dry/non-condensing gas on both the positive and negative pressure side.
DWT
- see dead weight tester.
dyn/cm²
- see dyne per square centimeter.
Dyne per Square Centimetre (dyn/cm²)
- is one of the smallest pressure units and is derived from the CGS unit for force where 1 Dyne equals 1 gram accelerated by 1 centimeter per second per second. 1 Dyne per Square Centimetre equals 0.1 Pascals.

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E

EPDM
- see ethylene propylene diene monomer.
Ethylene Propylene Diene Monomer (EPDM)
- type of rubber seal material which offers excellent resilience against solvents, antifreeze and aviation hydraulic fluids such as Skydrol and has an operating temperature range from -54 to +150 deg C (-65.2 to +302 deg F).

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F

Feet of H2O (ftH2O), Feet of Water Gauge (ftWG) or Feet of Water Column (ftWC)
- American and English low value pressure unit, now used mostly in the USA where feet and inches are the standard units for measuring distance. 1 Foot of Water Column at 4 degC (39.2 degF) equals 2989.07 Pascals.
FEP
- see fluorinated ethylene propylene.
Food Grade Compatible
- see hygienic.
FFKM
- see perfluoroelastomer.
FKM
- see fluoroelastomer.
Fluorinated Ethylene Propylene (FEP)
- resin coating that has a very high chemical and temperature resistance. Typically it is offered as an optional electrical cable coating on submersible pressure sensors where the liquid media is too aggressive for the more standard general purpose cable coatings.
Fluoroelastomer (FKM, Viton®)
- fluorinated carbon based rubber material which is mostly used on pressure measurement equipment to seal joints between components which are either pressurised or water-tight.
Flush Diaphragm
- type of diaphragm which is completely open and exposed to the pressure media and level with the surrounding surfaces when installed.
FRO
- see full range output.
FS
- see full scale and full span.
FSO
- see full scale output.
ftAq
- see foot of water.
ftH2O
- see foot of water.
ftWC
- see foot of water column.
ftWG
- see foot of water gauge.
Full Range Output (FRO)
- see full scale output.
Full Scale (FS)
- difference between the lowest and highest possible measurement point and provides a common term for defining specification parameters such as accuracy errors and overpressure ratings for devices which have many different pressure ranges.
Full Scale Output (FSO)
- is the resulting output signal or displayed reading produced when the maximum measurable pressure for a given device is applied.

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G

g
- see gauge reference and gravity.
Gauge Reference Pressure (g)
- pressure measured relative to atmospheric or barometric pressure.
g/cm²
- see grams per square centimeter.
g Effect
- change in performance of a pressure measuring device that is caused by a change in its orientation.
gf/cm²
- see grams force per square centimeter.
Grams per Square Centimetre (g/cm²) or Grams Force per Square Centimetre (gf/cm²)
- cgs system (centimetre, gram, second) pressure unit which is now largely obsolete and officially superceded by SI system of units. 1 Gram per Square Centimeter is 98.0665 Pascals.
Gravity (g)
- acceleration of 9.80665m/s² is the designated average accelerating force due to Earth's gravity at sea level.

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H

HART®
- see highway addressable remote transducer.
Heating, Ventilation and Air Conditioning (HVAC)
- applications on equipment used to manage environmental conditions inside large buildings, clean rooms and laboratories. There are many pressure sensors used on HVAC systems, typically low range differential pressure sensors are used to monitor air flow, medium range gauge pressure sensors are used to monitor water, steam, refrigerant and fuel pressures.
Hectopascal (hPa)
- 100x multiple of the Pascal which is the SI unit for pressure. The Hectopascal is the international unit for measuring atmospheric or barometric pressure. 1 Hectopascal equals 100 Pascals.
Highway Addressable Remote Transducer (HART®)
- type of digital communications protocol for configuring and reading instrumentation via the 4 to 20mA current loop. HART® data is communicated via a low level AC digital signal which is superimposed on a 2 wire 4-20mA current loop signal and functions simultaneously without interfering with the measurement output signal.
hPa
- see hectopascal.
HVAC
- see heating, ventilation and air conditioning.
Hydrostatic Pressure
- force per unit area generated by the weight of a column of liquid when it is at rest. The height of a liquid column of uniform density is directly proportional to the hydrostatic pressure.
Hygienic
- all parts in contact with the process media must have a high level of cleanliness and include precautions against contamination.
Hysteresis
- difference in measurement taken at exactly the same pressure but recorded directly after an increased change in pressure and a decreased change in pressure. This is caused by the natural reluctance of a pressure sensing material such as a diaphragm to return to its original position, shape or form after being flexed.

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I

Inch of H2O (inH2O), Inch of Water Gauge (inWG) or Inches of Water Column (inWC)
- English and American unit for measuring liquid level. 1 inch of water column at 4 degrees celsius equals 249.089 Pascals.
Inch of Mercury (inHg)
- British and American unit of measure for pressure. 1 inch of Mercury at 0 degrees Celsius (32 deg F) equals 3386.39 Pascals.
inAq
- see inch of water.
Ingress Protection (IP) Rating
- engineering standard for defining the protection of electrical equipment enclosures from the ingress of solids and liquids such as dust and humidity.
inH2O
- see inches of water.
inHg
- see inches of mercury.
inWC
- see inch of water column.
inWG
- see inches of water gauge.
IP Rating
- see ingress protection rating.
Isolation Diaphragm
- thin membrane which is used to isolate the media on one side of a diaphragm from media on the other side, whilst allowing the transmission of pressure with minimal loss.

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K

Kalrez®
- see perfluoroelastomer.
kg/cm²
- see kilograms per square centimeter.
kgf/cm²
- see kilograms force per square centimeter.
Kilogram per Square Centimeter (kg/cm²) or Kilogram Force per Square Centimeter (kgf/cm²)
- pressure unit which has largely been superceded by the SI unit system of pascal units. It is the metric equivalent of pounds per square inch (psi). 1 kg/cm2 equals 98,066.5 Pascals.
Kilopascal (kPa)
- 1000x multiple of the Pascal unit which is the SI unit for pressure. 1 Kilopascal equals 1,000 Pascals.
kPa
- see kilopascal.

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L

lb/ft²
- see pounds per square foot.
lbf/in²
- see pound force per square inch.
lb/in²
- see pounds per square inch.
Linear Variable Differential Transformer (LVDT)
- type of sensor which converts linear displacement into an variable electrical signal. An LVDT consists of a sliding ferromagnetic core which sits inside 3 electrical coils, a primary coil in the middle and two identical secondary coils at either side.
LVDT
- see linear variable differential transformer.
Long Term Stability or Long Term Drift
- amount of change of a measured reading at exactly the same pressure and ambient conditions over a given period of time which is typically quoted as an annual figure.

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M

mAq
- see meter of water.
Maximum Pressure Hysteresis
- largest difference between measurements recorded during an increase in pressure from zero to full scale pressure and a decrease in pressure from full scale to zero pressure.
mb
- see millibar.
mbar
- see millibar.
mbr
- see millibar.
Mean Sea Level (MSL)
- average height of the ocean surface. Mean sea level is a significant datum reference for meteorological and altitiude related pressure measurements, e.g. standard atmospheric pressure at sea level is 1013.25 hPa or 29.92 inHg.
Mean Time Between Failures (MTBF)
- theoretically calculated value which considers all the components used in the construction of a product. It may also be a statistically calculated value derived from real operational data collected from a sufficient number of the same product.
Mechanical Stop
- internal component which protects pressure sensing components from overpressure by limiting the deflection of the diaphragm. A mechanical stop will protect a pressure sensing device to a much higher pressure than one which relies on the natural overpressure rating of the sensing diaphragm.
Megapascal (MPa)
- 1000000x multiple of the Pascal unit which is the SI unit for pressure. 1 Megapascal equals 1,000,000 Pascals.
Metres of H2O (mH2O) , Metres of Water Gauge (mWG) or Metres of Water Column (mWC)
- metric unit for measuring liquid level. 1 metre of water column at 4 degrees Celsius equals 9806.65 Pascals.
mH2O
- see meter of water.
Microns of Mercury (µHg) or Micrometres of Mercury (µmHg)
- very small pressure unit which is derived from the pressure due to gravity that is generated by a 1 micrometer (1/1000mm) column of liquid mercury. 1 Micron of Mercury of Mercury at zero degrees Celsius equals 0.133322 Pascals.
Millibar (mbar, mb or mbr)
- metric unit of pressure mainly used in European countries and is derived directly from the Bar pressure unit which equals 1,000 mbar. In SI units 1 mbar equals 100 Pascals.
Millimetres of H2O (mmH2O) , Millimetres of Water Gauge (mmWG) or Millimetres of Water Column (mmWC)
- low range metric pressure unit derived from the hydrostatic pressure of 1mm head of water at 4 degC. 1 Millimeter of Water Gauge equals 9.80665 Pascals.
Millimetres of Mercury (mmHg)
- small Metric pressure unit which is derived from the hydrostatic pressure generated by a 1 mm tall column of mercury liquid. 1 Millimeter of Mercury equals 133.322 Pascals.
Millitorr (mTorr)
- very small pressure unit used for high vacuum measurements and is a 1/1000x multiple of the Torr pressure unit. 1 mTorr equals 0.133322 Pascals.
Millivolt per Volt Output Signal (mV/V, mV/V/bar, mV/V/psi)
- type of sensor signal which is typically produced by a transducer which has a wheatstone bridge strain gauge circuit.
mmAq
- see millimeters of water.
mmH2O
- see millimeters of water.
mmHg
- see millimeters of mercury.
mmWC
- see millimeters of water column.
mmWG
- see millimeters of water gauge.
MPa
- see megapascal.
MSL
- see mean sea level.
MTBF
- see mean time between failures.
mTorr
- see millitorr.
mV/V
- see millivolt per volt output signal.
mV/V/bar
- see millivolt per volt output signal.
mV/V/psi
- see millivolt per volt output signal.
mWC
- see meter of water column.
mWG
- see meter of water gauge.

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N

National Physical Laboratory (NPL)
- national measurement institute for the United Kingdom. This organisation is responsible for maintaining the primary measurement standards for the UK.
NC
- see normally closed.
Negative Gauge Pressure
- difference in pressure between any vacuum pressure and atmospheric pressure. The maximum possible negative gauge pressure is always limited by the current ambient atmospheric pressure, which constantly varies, but is typically around 1 bar absolute.
Newton per Square Metre (N/m2)
- pressure unit based on SI units for force and length which shows how the Pascal unit is derived. Pressure is defined as Force/Area and the SI unit for Force is Newtons (N) and the SI unit for Area is Sq Meters (m^2). 1 Newton per Square Metre equals 1 Pascal.
NLHR
- see non-linearity, hysteresis and repeatability.
N/m2
- see newton per square meter.
NO
- see normally open.
Non-Linearity
- deviation error derived from the straightness of a set of recorded pressures when compared to a perfectly straight line drawn through all the results. the maximum non-linearity error is normally expressed as a percentage of full scale.
Non-Linearity, Hysteresis and Repeatability (NLHR)
- often used to describe the room temperature precision of a pressure sensor, excluding all zero & span offsets, temperature errors and long term stability. Also see non-linearity and hysteresis.
Normally Closed (NC)
- electrical circuit switch contact which opens when the switch is activated. e.g. a pressure switch set at 10 bar will open once the pressure exceeds 10 bar.
Normally Open (NO)
- electrical circuit switch contact which closes when the switch is activated. e.g. a pressure switch set at 10 bar will close once pressures exceeds 10 bar.
NPL
- see national physical laboratory.

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O

Ounce per Square Inch (oz/in²) or Ounce Force per Square Inch (ozf/in²)
- low pressure unit which is part of the British and American system of units. 1 Ounce per Square Inch equals 430.922 Pascals.
Overpressure
- maximum pressure that can be applied to a pressure instrument without significantly effecting its reading accuracy. Some manufacturers will state a maximum calibration shift following an over-pressure condition where others will state that the specification is unaffected.
Oxygen Clean
- see oxygen service.
Oxygen Service
- safe to use on pure Oxygen or a gas containing a high concentration of Oxygen.
oz/in²
- see ounce per square inch.
ozf/in²
- see ounce force per square inch.

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P

Pa
- see pascal.
Parts Per Million (PPM)
- ratio used to describe the maximum measurement error or resolution of pressure measurement equipment. It is most often used as an alternative way of expressing very small percentage values for high accuracy primary pressure standards such as dead weight testers and high resolution digital displays.
Pascal (Pa)
- SI unit for pressure which is derived from other SI units using the following relationships: Pa = (kg.m/s²)/m² = kg/m.s² = N/m². Since 1 pascal is a very low pressure being 1/100 of a millibar it's use is limited to ultra low pressure applications such as measuring the pressure differences in ventilation systems.
Perfluoroelastomer (FFKM, Kalrez®, Chemraz®, Perlast®)
- seal material type which has a much higher temperature rating than the more common FKM and can be used on temperatures up to 300°C. FFKM also has a broader chemical resistance than FKM.
Perlast®
- see perfluoroelastomer.
pfsf
- see pounds force per square foot.
pfsi
- see pound force per square inch.
Piezoresistive Strain Gauges
- semiconductor material which generates a change in resistance when stressed.
Polyurethane (PUR, PU)
- durable polymer which is used as a coating for sensor cabling and as a sealing compound to keep out water and as a potting compound to protect electronics components from damage.
Polyvinyl Chloride (PVC)
- widely used plastic which is cheap to produce and hard enough to be used as a component parts construction material. PVC in a plasticised form is a softer, more flexible material, and is used to manufacture coatings, fabrics and linings.
Pounds per Square Foot (psf) or Pound Force per Square Foot (pfsf)
- British Imperial and American pressure unit which is directly related to the psi pressure unit by a factor of 144 (1 sq ft = 12 in x 12 in = 144 sq in). 1 Pound per Square Foot equals 47.8803 Pascals.
Pounds per Square Inch (psi or lb/in²) or Pound Force per Square Inch (pfsi or lbf/in²)
- widely used British and American unit of measure for pressure. 1 psi converts to 6,894.76 Pascals.
PPM
- see parts per million.
Precision
- is the measure of how closely grouped a set of readings are to each other.
Pressure
- amount of force applied to a unit area and calculated by dividing the applied force by the area of the surface being stressed. The SI unit for pressure is the Pascal (Pa) which is the name given to one Newton per square metre (N/m2).
Pressure Transducer
- device which converts an applied pressure into a measurable electrical signal.
Pressure Transmitter
- device that boosts the output signal of a pressure transducer so that it can be sent over a long distance without significant loss or interference of the signal.
Primary Pressure Reference Standard
- instruments which produce very high accuracy and stable pressures for the purpose of maintaining a measurement standard. These instruments are used to ensure that the measurement uncertainty of all pressure instrumentation which are referred to the standard are kept within performance requirements.
Proof Pressure
- see overpressure.
psf
- see pounds per square foot.
psi
- see pounds per square inch.
psia
- means pounds per square inch absolute.
psid
- means pounds per square inch differential.
psig
- means pounds per square inch gauge.
PU
- see polyurethane.
PUR
- see polyurethane.
PVC
- see polyvinyl chloride.

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R

Rangeable
- type of output signal from a pressure sensing device which can be adjusted by the operator to a different span of pressure. Also see turndown ratio.
Ratiometric
- indicates that the output signal level of a pressure measurement device will change in proportion to a change in supply input.
Reference Pressure
- pressure present on the reverse or negative side of a pressure sensing element. For example the pressure reading will be zero when the total pressure measured on the positive side of the diaphragm equals the reference pressure. Also see gauge reference and absolute reference.
Referred Temperature Error Band (RTE)
- maximum deviation expressed as a percentage of full scale in either the positive or the negative direction from the measurements at a defined temperature which is typically room temperature. This maximum deviation is then expressed as ±figure e.g. ±2.5%FS.
Repeatability
- amount of change of a measured reading at exactly the same pressure and ambient conditions over a series of pressure cycles from zero to full scale pressure and back to zero again. To ensure no Pressure Hysteresis is introduced into Repeatability measurement, readings are always taken during an increase in pressure or a decrease in pressure but never a mixture of the two.
RTE
- see referred temperature error.

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S

Sealed Gauge Reference Pressure (SG)
- pressure measured relative to a fixed approximation of atmospheric pressure by sealing atmospheric air pressure on the reference side of a pressure sensing device during manufacture. A preferred method of creating a sealed gauge reference is to seal a high vacuum on the reference side and subtract a 1 bar pressure offset from the measurement output.
Sea Level
- see mean sea level.
Secondary Pressure Standards
- instruments that cannot be used to measure Force and Area directly to derive a measurement of pressure but are still used as a traceable standard for calibrating other pressure instruments, e.g. an Electronic Pressure Calibrator that uses a Pressure Transducer inside would be classed as a Secondary Pressure Standard.
Semiconductor Strain Gauges
- see piezoresistive strain gauge.
SG
- see sealed gauge reference and specific gravity.
Silicon on Insulator (SOI)
- pressure sensing technology which enables sensing diaphragms to be used at much higher temperatures. Unlike ion implanted silicon strain gauge diaphragms SOI does not have P-N junctions that begin to breakdown at high temperatures producing leakage currents which cause unstable performance.
Silicon Pressure Sensors
- bring together the benefits of the high gauge factors of semiconductor strain gauge technology with the high elasticity of a Silicon sensing diaphragm. Silicon pressure transducers have high mV/V output signal sensitivity, high overpressure and very low non-linearity, hysteresis and repeatability.
SOI
- see silicon on insulator.
Span Output
- difference between the minium and maximum output signals of a pressure sensor.
Span Offset
- amount of deviation in maximum span output signal of a pressure sensor from the ideal value at full scale pressure. The span offset is normally expressed as percentage of full scale pressure or electrical units, e.g. ±0.5% FS or ±3mV.
Span Sensitivity
- defines the output signal characteristic of a pressure sensor and is expressed as a ratio of maximum span output signal divided by the pressure range, e.g. 10mV/bar. For ratiometric outputs that are proportional to supply voltage, the span sensitivity would be expressed as 10mV/V/bar.
Specific Gravity (SG)
- comparison ratio between the density of a sample liquid/gas and a reference liquid/gas. Since the density of the reference liquid/gas will vary depending on its temperature, the specific gravity should also include the temperature of the reference media.
Square Root Extraction
- linear differential pressure reading which has been mathematically processed by taking the square root of the reading and then dividing by the square root of full span to calculate the proportion of full scale signal to output. The flow of a gas or liquid through a closed pipe is proportional to the square root of the differential pressure, therefore the resulting square root extraction output provides a linear output for measuring flow.
Stability
- see long term stability.
Standard Atmosphere (atm)
- fixed reference value for the average barometric pressure at sea level. It is often used to indicate the depth rating for a water resistant watch, but otherwise is rarely used as a unit for measuring pressure. 1 Standard Atmosphere is defined as being exactly equal to 101,325 Pascals.
Static Line Pressure
- total pressure present at a particular point along a pressurised pipe. It is often quoted on the specifications for differential pressure sensors as an indicator of the maximum pressure that can be applied to both the high and the low side pressure ports at the same time. This should not be confused with the over-pressure limit which is related to the differential pressure range rather than the static line pressure.
Suction Pressure
- negative difference in pressure generated between two measurement points which draws a gas or a liquid from a higher to a lower pressure region.

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T

TEB
- see temperature error band and total error band.
Technical Atmosphere (at)
- similar, although not the same value as the Standard Atmosphere pressure unit (atm) and both have been used historically to relate a pressure value to multiples of atmospheric pressure. 1 Technical Atmosphere is defined as being exactly equal to 98,066.5 Pascals.
Temperature Compensation
- correction applied to a pressure measurement instrument to reduce errors attributed to temperature changes in the media being measured or the surrounding environment.
Temperature Error
- deviation of a pressure measurement reading with a change in media temperature.
Temperature Error Band (TEB)
- uncertainty error derived from the two measurement points that exhibit the greatest deviation in the positive and negative direction from measurements taken at the same pressure at room temperature, and then adding each together and expressing it as a percentage of full scale e.g. 2%FS. This is often expressed as a ±figure by dividing the Total Error Band by two e.g. ±1%FS.
Terminal Straight Line Accuracy
- limit of uncertainty that any pressure measurement reading will deviate from the terminal straight line.
Terminal Straight Line (TSL)
- straignt line drawn between the measurement output at zero and full scale pressure.
TFSF
- see tons force per square foot.
TFSI
- see tons force per square inch (uk) and tons force per square inch (usa).
Thermal Hysteresis
- measured change in output or reading at a specific pressure and temperature taken during a sequence of increasing and decreasing temperature.
Thermal Span or Sensitivity Shift (TSS)
- maximum amount the span output or reading could change at any point within the compensated temperature range. This error is normally expressed either as a percentage of full scale output or reading. It can also be expressed as a percentage of full scale per degC, degF or K e.g. ±0.01%FS/DegF.
Thermal Zero Shift (TZS)
- maximum amount the output or reading at zero pressure might deviate over the compensated temperature range. This error is typically expressed as a percentage of full scale output or reading. It can also be expressed as percentage of full scale per degC, degF or K e.g. ±0.02%FS/DegC.
Threshold
- amount of pressure change required before a pressure measuring instrument reacts with a change in measurement output or produces a specified result.
Tons per Square Foot (tsf), USA, Short or Tons Force per Square Foot (tfsf), USA, Short
- American pressure unit comparable in magnitude to atmospheric pressure. 1 Ton per Square Foot (USA, Short) equals 95760.5 Pascals.
Tons per Square Inch (tsi), UK, Long or Tons Force per Square Inch (tfsi), UK, Long
- very large pressure unit used historically for measuring extremely high pressures. 1 Ton per Square Inch equals 15,444,300 Pascals.
Tons per Square Inch (tsi), USA, Short or Tons Force per Square Inch (tfsi), USA, Short
- one of the largest pressure units and is used in the measurement of ultra high pressures. 1 Ton per Square Inch (USA, Short) equals 13,789,500 Pascals.
Torr
- pressure unit which is defined as 1 Standard Atmosphere divided by 760 (1 atm/760 or 101325 Pa/760). Used mostly for measuring high vacuum, the Torr has largely been superceded by the hPa (mbar) pressure unit. 1 Torr equals 133.322 Pascals.
Total Error Band (TEB)
- difference between the most negative and most positive deviation from the true pressure, determined from the combination of all known errors for a pressure sensing device, within the constraints of a pressure measurement and operating temperature range.
Traceable Calibration
- calibration was performed using equipment which has been routinely calibrated to a standard that can be traced back to a national or international measurement standard.
Transducer
- device which converts the measurement of a non-electrical parameter such as temperature or pressure into an electrical output signal. Also see pressure transducer.
Transmitter
- device which converts a sensor output into an analogue signal suitable for sending over long distances without significant signal loss or interference. The signal typically used is a 4 to 20 mA current loop output. Also see pressure transmitter.
TSF
- see tons per square foot.
TSI
- see tons per square inch (uk) and tons per square inch (usa).
TSL
- see terminal straight line.
TSS
- see thermal span shift.
Turndown Ratio
- describes the difference between the highest and lowest possible span of pressures which can be set for a pressure sensing device with a rangeable output signal such as 4 to 20mA or 0 to 10 Vdc. Also see rangeable.
Tx
- see transmitter.
TZS
- see thermal zero shift.

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U

UKAS
- see united kingdom accreditation service.
UKAS Calibration Certificate
- formal document including the UKAS royal crown logo, issued by a UKAS certified calibration laboratory for a pressure calibration that it has completed, which includes test results, pass/fail analysis, equipment used, device tested, location, environmental conditions, recipient details, calibrating organisation and personnel details. Also see united kingdom accreditation service.
United Kingdom Accreditation Service (UKAS)
- national organisation recognised by the UK government which audit and certify pressure calibration standard laboratories in the United Kingdom, so that those who use the calibration services of a UKAS accredited laboratory are assured that the pressure calibration will be carried out to a very high standard.

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V

Vacuum
- range of pressures which exist between zero absolute pressure and atmospheric pressure.
Vented Cable
- type of signal cable which has 1 or 2 vent tubes running through its core which are used to expose the reference side of a gauge reference pressure sensor to outside air pressure.
Vented Gauge Reference Pressure (VG)
- pressure measured with an instrument that has the negative side of the pressure sensing device constantly open to atmospheric air pressure.
VG
- see vented gauge reference.
Viton®
- see fluoroelastomer.

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W

Water Density
- at a temperature of approximately 4 degrees Celsius it is 1000 kg/m3
Wet/Dry
- differential pressure measurement device which is compatible with liquid on the positive pressure side and dry/non-condensing gas on the negative pressure side.
Wetted Parts
- components of pressure sensing device which are in contact with the liquid media being measured.
Wet/Wet
- differential pressure measurement device which is compatible with liquid on both the positive and negative pressure side.
Wheatstone Bridge Strain Gauge
- type of electrical circuit which is used extensively inside pressure transducers to convert mechanical stress caused by a change in pressure into an electrical output signal.

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Z

Zero Offset
- deviation in output or reading from the ideal point at zero pressure.
Zero Tare
- operation of removing any Zero Offset to obtain the optimum measurement at zero pressure.

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Numeric

1000 kg/m³
- see water density.
1013.25 mbar abs
- see standard atmosphere.
2 wire
- type of electrical connection for a measurement or control signal which has just two connections which provide both the device power supply and the signal output. The most common example is a 2 wire 4-20mA current loop output.
29.92 inHg abs
- see standard atmosphere.
3 wire
- type of electrical connection for a measurement or control signal which has three connections for both power supply and signal output. A typical example is a 0 to 10 volt output, where there is a separate supply positive, output positive and shared supply/output negative conection.
4-20mA Current Loop Output
- common type of electrical signal used by the process control industry to provide a robust measurement signal that can be passed through several devices as part of series circuit without significant loss of signal.
9.80665 m/s²
- see gravity.
Glossary Index

A | B | C | D | E | F | G | H | I

J | K | L | M | N | O | P | Q | R

S | T | U | V | W | X | Y | Z

Numeric




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Tools
  • Pressure Conversion




    Converts to



  • IP Ratings Explained

    I P

    First Digit (Solids)
    No protection

    Second Digit (Liquids)
    No protection

  • Temperature Conversion




    Converts to



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