Definitions, Technical Terms And Glossary
2 wire output
Type of electrical connection for a measuring element or transmitter that provides power supply and output 4-20mA signals to the data logger or control system at the same time with a pair of wires.
3 wire output
Type of electrical connection for a measuring element or transmitter that provides power supply and output of DC voltage (e.g. 0-10V, 0-5V, etc. ) signals to the data logger or control system at the same time with a pair of wires.
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.
Absolute pressure (Abs, a)
Absolute pressure is defined as the sum of a system’s gauge, or measured, pressure and the pressure of the atmosphere that is referred to the vacuum of free space (zero pressure). In practice, absolute Piezo-resistive pressure sensors measure the pressure relative to a high vacuum reference sealed behind its sensing diaphragm. The vacuum has to be negligible compared to the pressure to be measured.
Accuracy
Stated as a limit tolerance which defines the average deviation between the actual outputs versus theoretical output. In practical transducer applications, the potential errors of nonlinearity, hysteresis, non-repeatability and temperature effects do not normally occur simultaneously, nor are they necessarily additive. Therefore, accuracy is calculated based upon the RMS value of potential errors, assuming a temperature band of ± 10° C, full rated load applied, and proper set up and calibration. Potential errors of the readout, crosstalk, or creep effects are not included.
Ambient Pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object. The atmospheric pressure or pressure in the environment or surrounding area. It is given a reference value of zero (0) cm H2O.
Atmospheric Pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth (or that of another planet).
Axial Load
A load applied along a line concentric with the Primary Axis.
Bandwidth (signal processing)
A measure of the width of a range of frequencies, measured in hertz.
bar (unit)
The bar is a unit of pressure defined as 1,000,000 dynes per square centimetre (or equivalently in SI units, 100kilopascal or in CGS units, 1 mega-barye). It is about equal to the atmospheric pressure on Earth at sea level.
barD
Differential pressure unit.
barg
A unit of gauge pressure.
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
Bonded Seal
A metal washer with a vulcanised rubber bonded to its inside diameter, which is used for high pressure applications to provide a pressure seal when placed between two flat surfaces that are screwed together using a male and female parallel thread.
Bourdon Tube
A flattened length of thin hollow metal tubing which is formed into an arc of a circle of 270 to 300°.
Burst Pressure
A design safety limit which should not be exceeded to prevent damage of sensing element, mechanical breach or permanent loss of pressure containment.
Calibration
A comparison of measurements. The device with the known or assigned correctness is called the standard.
Calibration Curve
A general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. A record of the comparison of the transducer outputs versus standard test loads.
Cardinal Points (Calibration)
Markings around the outside of an analogue pressure gauge dial which define the increments of pressure
Centimetres of H2O (cmH2O),
Manometric unit used to relate a pressure reading to the height of fresh water at a temperature of 4°C. 1 Centimetre of Water Gauge equals 98.0665 Pascals. It known as Centimetres of Water Gauge (cmWG) or Centimetres of Water Column (cmWC) as well
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 centimetre of mercury at zero degrees Celsius equals 1333.22Pascals.
Ceramic Pressure Transducer
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.
Compensated Temperature (engineering)
The range of temperature over which the transducer is compensated to maintain Rated Output and Zero Balance within specified limits. Temperature compensation is the utilization of supplementary devices, materials, or components within the bridge to minimize sources of error caused by changing temperature.
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.
Dead band
Region of pressure where a change in pressure produces no change in measurement output or control signal.
Deflection (engineering)
The displacement or degree of a structural element under load.
Differential pressure (DP, Delta P)
Differential pressure is the difference between any two process pressures. Differential pressure sensors have two separate pressure ports and can be calibrated to measure both positive and negative differential pressures (bidirectional pressure measurement).
Commonly difference in pressure of separate points in a system shown by ΔP.
Digital Compensation
Process of minimizing the error over the desired frequency range to correct the digital output of a pressure transmitter so that the pressure accuracy and thermal errors can be improved.
Digital signal processing
MeasureX’ pressure sensors with digital signal conditioning electronically correct the sensor signal and compensate for all error sources such as offset, span, temperature effects, non-linearity and hysteresis all at the same time.
The analogue mV pressure signal and the corresponding temperature information from the measuring bridge are amplified and digitally converted. A microcontroller calculates the corrected pressure value using a special mathematical algorithm and sensor specific compensation coefficients which have been stored in the microcontroller memory. These exact coefficients have been determined by the temperature and pressure cycling of each device during production. The final sensor signal is available via a digital bus interface (e.g. I²C, SPI) and as an analogue voltage output signal.
Drift
A continuous change in Output under constant Load conditions.
Dyne per Square Centimetre (dyn/cm²)
One of the smallest pressure units and is derived from the CGS unit for force where 1 Dyne equals 1 gram accelerated by 1 centimetre per second per second. 1 Dyne per Square Centimetre equals 0.1 Pascals.
Emissivity
The emissivity of a material (usually written ε or e) is the relative ability of its surface to emit energy by radiation. The emissivity of an object depends upon its material and surface texture. A polished metal surface can have an emissivity around 0.2 and a piece of wood can have an emissivity around 0.95.
Error
The algebraic difference between the indicated and true value of the load being measured. See Accuracy.
Excitation
The voltage or current applied to the input terminals of the measuring system or device.
Feet of H2O (ftH2O),
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°C (39.2°F) equals 2989.07 Pascals. It known as Feet of Water Gauge (ftWG) or Feet of Water Column (ftWC) as well.
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.
Flush Diaphragm
Type of diaphragm which is completely exposed to the pressure media and level with the surrounding surfaces when installed.
FMEA
Failure Modes and Effects Analysis is a systematic methodology for analysing and documenting all of the possible failure causes of a part, assembly, subsystem or system. Each individual component is evaluated to determine the ways in which it might fail along with the probability of failure and the consequences if that failure occurs. Design engineers then use this information to take steps to mitigate the effect of critical failures. MeasureX uses FMEA processes to help identify single-point failures to ensure that we are providing the most robust sensors possible.
Food Grade Compatible
See hygienic.
Frequency response
The quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. is characterized by the magnitude of the system’s response, typically measured in decibels (dB) or as a decimal, and the phase, measured in radians or degrees, versus frequency in radians/sec or Hertz (Hz).
Full Range Output (FRO)
See full scale output.
Full Scale / Full Span (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)
It is the algebraic difference between the upper and lower limit of the electrical output signals when minimum and maximum inputs applied on the measuring sensors.
Gage pressure
Gage pressure is the pressure relative to the local atmospheric or ambient pressure. The average atmospheric pressure at sea level is 1013.25 mbar. Changes of the atmospheric pressure due to weather conditions or altitude directly influence the output of a gage pressure sensor and are therefore compensated.
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 superseded by SI system of units. 1 Gram per Square Centimetre is 98.0665 Pascals.
Gravity (g)
The force of attraction by which terrestrial bodies tend to fall toward the centre of the earth. It is a unit of acceleration equal to the acceleration of gravity. Acceleration of 9.80665m/s² is the designated average accelerating force due to Earth’s gravity at sea level.
Hecto-Pascal (hPa)
Hecto-Pascal is the international unit for measuring atmospheric or barometric pressure. 1 hPa= 100 Pa
Highway Addressable Remote Transducer Protocol (HART®)
HART® is a digital industrial automation protocol for configuring and reading instrumentation via 4 to 20mA current loop.
Hydrostatic Pressure
The pressure exerted by a column of liquid of height h and density ρ is given by the hydrostatic pressure equation p = ρgh.
Hygienic
All parts in contact with the process media must have a high level of cleanliness and include precautions against contamination.
Hysteresis
The maximum difference between the transducer output readings for the same applied load (pressure or etc.); one reading obtained by increasing the load from zero and the other by decreasing the load from Rated Output. Usually measured at half Rated Output and expressed in percent of Rated Output. Measurements should be taken as rapidly as possible to minimize Creep. This is caused by the natural reluctance of a sensing material such as a diaphragm to return to its original position, shape or form after being flexed.
Electrical Hysteresis occurs in ferromagnetic materials and ferroelectric materials, as well as in the deformation of some materials (such as rubber bands and shape-memory alloys) in response to a varying force.
Inch of H2O (inH2O)
English and American unit for measuring liquid level. 1 inch of water column at 4 degrees Celsius equals 249.089 Pascals. It is known as Inch of Water Gauge (inWG) or Inches of Water Column (inWC) as well.
Inch of Mercury (inHg)
British and American unit of measure for pressure. 1 inch of Mercury at 0 degrees Celsius (32°F) equals 3386.39 Pascals.
Ingress Protection (IP) Rating
IP ratings are developed by the European Committee for Electro Technical Standardization (CENELEC) (NEMA IEC 60529 Degrees of Protection Provided by Enclosures – IP Code), specifying the environmental protection of electrical equipment enclosures from the ingress of solids and liquids such as dust and humidity.
Isolation Diaphragm
Thin membrane seal 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.
Kilogram per Square Centimetre (kg/cm²)
Pressure unit uses metric units that equivalent of pounds per square inch (psi). 1 kg/cm2 equals 98,066.5 Pascals. It known as or Kilogram Force per Square Centimetre (kgf/cm²) as well.
Kilo-Pascal (kPa)
1000x multiple of the Pascal unit which is the SI unit for pressure. 1 Kilopascal equals 1,000 Pascals.
Linear Variable Differential Transformer (LVDT)
Type of electrical transformer or sensor which converts linear displacement into a 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.
Load
The weight, torque, or force applied to the sensing element.
Load Cell
A transducer which converts a force into electrical output signals that proportional to the applied weight or force.
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.
Maximum Surge Pressure
Safe pressure for the switch housing but which may damage the mechanism by continuous or repetitive application.
Mean Sea Level (MSL)
Average height of the ocean surface. Mean sea level is a significant datum reference for meteorological and altitude related pressure measurements, e.g. Standard atmospheric pressure at sea level is 1013.25 hPa or 29.92 inHg.
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.
Mega-Pascal (MPa)
1000000x multiple of the Pascal unit which is the SI unit for pressure. 1 Mega-Pascal equals 1,000,000 Pascals.
Metres of H2O (mH2O)
Metric unit for measuring liquid level. 1 metre of water column at 4 degrees Celsius equals 9806.65Pascals. It is known as Metres of Water Gauge (mWG) or Metres of Water Column (mWC) as well.
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 1micrometre (1/1000mm) column of liquid mercury. 1 micron of mercury of mercury at zero degrees Celsius equals 0.133322Pascals.
Millibar (mbar, mb or mbr)
Metric unit of pressure that 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)
Low range metric pressure unit derived from the hydro-static pressure of 1mm head of water at 4 degrees Celsius, 1millimetre of Water Gauge equals 9.80665 Pascals. It is known as millimetres of Water Gauge (mmWG) or Millimetres of Water Column (mmWC) as well.
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. 1millimetre of Mercury equals 133.322 Pascals.
Millivolt per Volt Output Signal (mV/V, mV/V/bar, mV/V/psi)
Type of sensor output signal which is typically produced by a transducer which has a Wheatstone bridge strain gauge circuit. 1 volt = 1000 millivolts
Natural Frequency
The frequency of free oscillation once the system is set into motion (vibration) without any external force applied.
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 Meter (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 (m2). 1 Newton per Square Metre equals 1 Pascal.
Non- Linearity, Hysteresis and Repeatability (NLHR)
An accuracy or precision specification refers to the maximum deviation of the sensor output from a straight line over the specified operating pressure range excluding zero-offset. The straight line can be determined using different methods such as Best Fit Straight Line (BFSL) or Terminal Base Line (TBL). The Best Fit Straight Line is fitted such that the positive and negative distances to the actual sensor output are minimised (least squares method). The Terminal Base Line runs through the start and end point of the sensor output. Non-linearity according to TBL can be much larger as if using BFSL.
Non-repeatability
The maximum deviation between repeated output readings when the same measuring value is approached from the same direction (either increasing or decreasing pressure) under the same operating conditions.
Normally Closed (NC)
Electrical circuit switch contact which opens when the switch is activated. E.g. A pressure switch set at 10bar will open once the pressure exceeds 10bar.
Normally Open (NO)
Electrical circuit switch contact which closes when the switch is activated. E.g. A pressure switch set at 10bar will close once pressures exceeds 10bar.
Operating Temperature
The extremes of temperature within which the transducer will operate without permanent adverse change to any of its performance characteristics.
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.
Overload Protection
Protects the load cell from accidental overloading above the rated capacity. MEASUREX has integrated this unique feature in most of its low capacity product.
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.
Piezoresistive pressure sensors
Silicon-based Piezo-resistive pressure sensors are made from a thin diaphragm in which resistors are embedded to form a Wheatstone bridge. When pressure is applied to the diaphragm, the electrical resistivity changes due to the mechanical stress (Piezo-resistive effect). If the bridge circuit is supplied with a voltage, a sensor output signal proportional to pressure is generated.
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.
Position sensitivity
Piezoresistive silicon pressure sensors with extremely low pressure ranges of only a few millibars feature a very thin diaphragm which may also show sensitivity to forces which are not caused by the applied pressure but by the sensor moving and changing position.
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.
Precision
The specification of how closely grouped a set of readings are to each other. See repeatability as well.
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 Axis
The axis along which the transducer is designed to be loaded; normally its geometric centre line.
Proof pressure (Overpressure)
Proof pressure is the maximum pressure which may be applied without causing durable shifts of the electrical parameters of the sensing element. Exposure to pressures above the proof pressure may lead to the sensor permanently not complying with its specification.
Range
The span of differential pressures or flow rates within which the sensing element of a given switch can be set to actuate an electric switch.
Rated Load (Rated Capacity)
The maximum Axial Load that the transducer is designed to measure within its specifications.
Rated Output
The signal (voltage) produced by the transducer. Where the output is directly proportional to excitation, the signal is expressed in terms of millivolts / volt (mV/V) of excitation.
Rated Pressure
The maximum pressure that the actuating components of the switch in contact with the media can withstand continuously and/or repeatedly without risk of permanent damage.
Ratiometric output signal
For ratiometric pressure sensors the output signal behaves proportional to the supply voltage. If for example the supply voltage for a sensor with 0.5…4.5 V output at 5 V supply increases by 10 % to 5.5V, the output signal also increases by 10 % to 0.55…4.95 V. In contrast, sensors with an internal reference voltage have a non-ratiometric output signal.
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.
Resolution
The smallest change in mechanical input which produces a detectable change in the output signal.
Safe Overload
The maximum load in percent of Rated Capacity which can be applied without producing a permanent shift in performance characteristics beyond those specified.
sampling rate
The number of times per second an analogue to digital converter takes a readings and converts per second.
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.
Set or Actuation Point
The exact air pressure or flow rate which will cause the electric switch to actuate.
Shunt Calibration
Electrical stimulation of transducer output by insertion of known shunt resistors between appropriate points within the circuitry.
Silicon
Silicon offers special benefits when it comes to manufacturing Piezo-resistive pressure sensor chips. Due to its single crystal structure, it shows no plastic deformation but returns to its original state without deformation after pressure loading. Material fatigue and hysteresis effects are therefore virtually eliminated. The semiconductor resistors implanted in the silicon sensor diaphragm are highly sensitive to even the smallest pressures and allow for full scale ranges of only a few millibars.
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
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 Output
Difference between the minimum and maximum output signals of a pressure sensor.
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.
Spectral linewidth
the width of an atomic or molecular spectral line, measured in hertz
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
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.
TDL
TDL stands for Transducer Description Language. Similar to a computer language TDL allows storage of TEDS parameters in the most space efficient manner. This data compression is needed due to the limited amount of storage space available in typical TEDS memory.
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.
TEDS
TEDS stands for Transducer Electronic Data Sheet based on the IEEE 1451.4 standard. It contains relevant information relating to the sensor, such as serial numbers, calibration factors or manufacturer specific information.
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 effects
The temperature effect specifies the maximum deviation of the output signal due to temperature changes over the sensor’s operating temperature range relative to a reference temperature (e.g. 25°C). A distinction is made between the temperature effect of offset and the temperature effect of span. The temperature effect is often specified as a temperature coefficient expressed as % per °C. Temperature effects may be caused by changes in the temperature of the medium as well as changes in the ambient temperature.
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.
Temperature Shift Span
The change in Output due to a change in transducer temperature. Expressed as a percentage of load per degree Fahrenheit (Celsius) change temperature.
Temperature Shift Zero
The change in Zero Balance due to a change in transducer temperature. Expressed as the change in Zero Balance in percent of Rated Output per degrees Fahrenheit (Celsius) (change in temperature).
Terminal Straight Line (TSL)
Straight line drawn between the measurement output at zero and full scale pressure.
Terminal Straight Line Accuracy
Limit of uncertainty that any pressure measurement reading will deviate from the terminal straight line.
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 °C, °F or k e.g. ±0.01%FS/°F.
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 °C, °F or k e.g. ±0.02%fs/°C.
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 superseded by the hPa (mbar) pressure unit. 1 Torr equals 133.322 Pascals.
Total accuracy Total error band
The sensor’s maximum total error over the compensated temperature range. With MeasureX’ pressure sensors, total accuracy includes all errors from offset and span calibration, temperature effects, non-linearity and hysteresis. Total accuracy is also referred to as Total Error Band (TEB).
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
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.
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.
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.
Vacuum
Pressure below atmospheric pressure is called negative or vacuum gage pressure. In general a vacuum is a volume of space that is essentially empty of matter. According to its quality vacuum is divided into different ranges such as low, high and ultra-high 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.
Viton®
See fluoroelastomer.
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
Wet/Wet
Differential pressure measurement device which is compatible with liquid on both the positive and negative pressure side.
Wetted Parts
Components of pressure sensing device which are in contact with the liquid media being measured.
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.
Zero Balance
The output signal of the transducer with rated Excitation and with no-load applied, usually expressed in percent of Rated Output.
Zero Offset
Deviation in output or reading from the ideal point at zero pressure.
Zero Return
The difference in Zero Balance measured immediately before Rated Load application of specified duration and measured after removal of the load, and when the output has stabilized.
Zero Stability
The degree to which the transducer maintains its Zero Balance with all environmental conditions and other variables remaining constant.
Zero Tare
Operation of removing any Zero Offset to obtain the optimum measurement at zero pressure.
1000 kg/m³
See water density.
1013.25 millibars
1 atmosphere (atm)=101 325 Pascals
29.92 inHg
See absolute barometric pressure. 29.92 inches of mercury = 101 309.12 Pascals
9.80665 m/s²
See standard gravity on earth.
NATA
National Association of Testing Authorities, Australia
