Float activated switches for opening or closing electrical contacts at a preset fluid level.

# Definitions

Definitions for measurement terms

## Vibrating Tuning Fork Fluid Level Detection

Vibrating tuning fork switches for opening or closing electrical contacts at a preset fluid level.

## Conductive Fluid Level Detection

Conductive sensing for detecting when a preset fluid level has been reached.

## Capacitive Fluid Level Measurement

Capacitance method for measuring the level of a fluid.

## Radar Distance Sensing

Radar method of measuring distance from a solid or liquid.

## Ultrasonic Distance Sensing

Ultrasonic method of measuring distance from a solid or liquid.

## Positive Displacement Flow Measurement

Positive displacement (PD) volumetric flow rate measurement.

## Vortex Flow Measurement

Vortex shedding von Karman effect flow measurement.

## Transit Time Flow Measurement

Using upstream and downstream ultrasonic transit time difference to measure flow velocity.

## Ultrasonic Flow Velocity Sensors

Ultrasound acoustic wave fluid flow velocity sensors.

## Doppler Effect Flow Measurement

How the Doppler effect acoustic frequency shift principle is used in flow measurement instrumentation.

## Volumetric Flow Rate

Measuring the volume of a substance that has passed a particular point in a specified time period.

## Mass Flow Rate

Measuring the mass of a substance that has passed a particular point in a specified time period.

## Landfill Sites

A landfill site is an area of land that is used to bury waste material.

## Strain Gauge

Resistive strain gauge device.

## Thin Film

Thin film deposition surface layer.

## Turbine Rotor Sensor

Turbine rotor blade and motion sensor for measuring speed of a substance.

## Paddle Wheel Sensor

Paddle wheel impeller and magnetic pickup sensor.

## Totalizer

Total accumulated quantity of substance transferred.

## USB

Universal Serial Bus (USB) interface computer connection

## Pressure Sensors

Pressure sensing devices

## ksi – Kilopounds per Square Inch Pressure Unit

The ksi pressure unit is derived from the psi pressure unit by multiplying it by 1,000, and the full name is kilopounds force per square inch.

## mPa – Millipascal Pressure Unit

Find conversions for the mPa (Millipascal) pressure unit.

## N/mm² – Newton per Square Millimetre Pressure Unit

Find conversions for the N/mm² (newtons per square millimetre) pressure unit.

## N/cm² – Newton per Square Centimetre Pressure Unit

Find conversions for the N/cm² (newtons per square centimetre) pressure unit.

## kg/mm² – Kilogram per Square Millimetre Pressure Unit

Find conversions for the kg/mm² (kilograms per square millimetre) pressure unit.

## ATEX

ATEX is the European Directive for governing health and safety in explosive environments.

## 4 Wire

4 wire describes a sensor which has a either a wheatstone bridge strain gauge configuration or a amplified output sensor where the supply input is isolated from the signal output. 4 wire is also used to describe a resistive thermometer that is wired so that the error caused by the connecting wire on each side […]

## Amplified Voltage Output

Amplified Voltage Output is convenient and robust measurement signal over medium distances to use with analogue to digital converters.

## Vented Gauge

Vented Gauge (VG) is a pressure referenced to atmospheric pressure via a vent path on the reverse side of the pressure sensing diaphragm.

## Pressure Units

There are many types of pressure units used depending on the country, industry and application.

## Hysteresis

Hysteresis is the difference of two separate measurements taken at the same point, before and after a physical quantity is increased and decreased.

## bar Pressure Unit

The bar is a widely used metric unit of measurement for pressure and 1 bar equals precisely 100,000 pascals.

## cmH2O – Centimetres of Water Column at 4 deg C Pressure Unit

Centimeters of Water Column is a 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.

## Deadband

Deadband is a region of pressure where a change in pressure produces no change in measurement output or control signal.

## g Effect

The g Effect is a change in performance of a pressure measuring device that is caused by a change in its orientation. Typically a pressure sensing device will have some form of flat diaphragm which will generate a change in output when flexed by a change in pressure. If a pressure sensing diaphragm is orientated […]

## cmHg – Centimetres of Mercury at 0 deg C Pressure Unit

Centimeters of Mercury is a 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. The use of cmHg is not as common as mmHg, it is mainly used in applications for […]

## g/cm² – Grams per Square Centimetre Pressure Unit

Grams Force per Square Centimetre is a cgs system pressure unit which is now largely obsolete and officially superceded by the SI system of units.

## g – Acceleration due to Gravity

Gravity (g) which is defined by an acceleration of 9.80665m/s² is the designated average accelerating force due to Earth’s gravity at sea level.

## hPa – Hectopascal Pressure Unit

Hectopascal is a 100x multiple of the pascal which is the SI unit for pressure.

## HART®

HART® or Highway Addressable Remote Transducer is a type of digital communications protocol for configuring and reading instrumentation via 4-20mA signal.

## Hydrostatic Pressure

Hydrostatic pressure is the pressure that is generated by the weight of liquid above a measurement point, when the liquid is at rest.

## dyn/cm² – Dyne per Square Centimetre Pressure Unit

Dyne per Square Centimeter is one of the smallest pressure units and is derived from the CGS unit for force, 1 Dyne per Square Centimetre equals 0.1 pascals.

## EPDM – Ethylene Propylene Diene Monomer

EPDM is a type of rubber seal material which offers excellent resilience against solvents, antifreeze and aviation hydraulic fluids.

## inH2O – Inches of Water Column at 4 deg C Pressure Unit

Inches of water gauge or column is an english and american unit for measuring liquid level. 1 inch of water column at 4 degrees celsius equals 249.089 Pa.

## ftH2O – Feet of Water Column at 4 deg C Pressure Unit

Foot of Water Column is an American and English low value pressure unit

## inHg – Inches of Mercury at 0 degrees C Pressure Unit

Inch of Mercury is a British and American unit of measure for pressure. 1 inch of mercury at 0 degrees Celsius (32 deg F) equals 3386.39 pascals. An inch of mercury at zero degrees Celsius is defined as the pressure exerted by a column of mercury with a density of 13,595.1 kg/m3 under the pull […]

## kg/cm² – Kilogram per Square Centimetre Pressure Unit

Kilogram Force per Square Centimeter is a pressure unit that has been largely superseded by the SI unit system of pascal units.

## kPa – Kilopascal Pressure Unit

The kilopascal is a x1000 multiple of the pascal unit which is the SI unit for pressure. 1 kilopascal equals 1,000 Pascals.

## LHR – Linearity, Hysteresis and Repeatability

Linearity, Hysteresis and Repeatability (LHR) is 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 pressure hysteresis.

## oz/in² – Ounce per Square Inch Pressure Unit

Ounce or Ounce Force per Square Inch is a low pressure unit which is part of the British and American system of units.

## PPM – Parts Per Million

Parts Per Million (PPM) is a ratio used to describe the maximum measurement error or resolution of pressure measurement equipment.

## MPa – Megapascal Pressure Unit

The megapascal is a x1000000 multiple of the pascal unit which is the SI unit for pressure. 1 megapascal equals 1,000,000 pascals.

## Pa – Pascal Pressure Unit

Pascal is the SI unit for pressure and is derived from other SI units using the following relationship: Pa = (kg.m/s²)/m² = kg/m.s² = N/m².

## mH2O – Metres of Water Gauge at 4 deg C Pressure Unit

Meters of water gauge or column is a metric unit for measuring liquid level. 1 metre of water column at 4 degrees Celsius equals 9806.65 pascals.

## µHg – Micron of Mercury at 0 deg C Pressure Unit

Micron of Mercury is a very small pressure unit derived from the pressure that is generated by a 1 micrometer (1/1000mm) column of liquid mercury.

## mbar – Millibar Pressure Unit

Millibar is a metric unit of pressure mainly used in European countries and is derived directly from the bar pressure unit which equals 1,000 mbar.

## mmH2O – Millimetres of Water Column at 4 deg C Pressure Unit

Millimeters of Water Column is a low range metric pressure unit derived from the hydrostatic pressure of 1mm head of water at 4 degC.

## mmHg – Millimetres of Mercury at 0 deg C Pressure Unit

Millimeters of Mercury at a temperature of 0degC is a small metric pressure unit derived from the pressure generated by a 1mm tall column of mercury liquid.

## mTorr – Millitorr Pressure Unit

Millitorr is a very small pressure unit used for high vacuum measurements and is a 1/1000x multiple of the torr pressure unit.

## Negative Gauge Pressure

Negative Gauge Pressure is the difference in pressure between any vacuum 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.

## N/m2 – Newton per Square Metre Pressure Unit

Newtons/Square Meter is a unit that shows how the pascal unit is derived from other SI units. 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. The N/m² pressure unit is one […]

## Reference Pressure

Reference Pressure is the pressure present on the reverse or negative side of a pressure sensing element.

## SG – Sealed Gauge

Sealed Gauge (SG) is a type of reference pressure measured relative to a fixed pressure of approximately 1 bar absolute.

## Secondary Pressure Standard

Secondary Pressure Standards are pressure calibration instruments which have to be checked by primary pressure standards on a regular basis.

## Threshold

Threshold is the amount of measurement change required before a measuring instrument reacts with a change in measurement output or produces a specified result.

## tsf – Tons per Square Foot (USA, Short) Pressure Unit

Tons or Tons Force per Square Foot (USA, Short) is an American pressure unit comparable in magnitude to atmospheric pressure.

## Dead Weight Tester

A Dead Weight Tester is an instrument which uses metal weights and a piston/cylinder assembly to generate pressure calibration setpoints to a high accuracy.

## Piezoresistive Strain Gauges

Piezoresistive strain gauges are a semiconductor material which changes in resistance when the material stretched or compressed.

## Specific Gravity

Specific gravity is a comparison ratio between the density of a particular substance and the density of a reference substance.

## psf – Pounds per Square Foot Pressure Unit

Pounds Force per Square Foot is a British (Imperial) and American pressure unit which is directly related to the psi pressure unit by a factor of 144.

## psi – Pounds per Square Inch Pressure Unit

Pounds or pound force per square inch (psi, lb/in², pfsi or lbf/in²) is a widely used British and American unit of measure for pressure.

## atm – Standard Atmosphere Pressure Unit

Standard Atmosphere is mainly used as a reference value for the average atmospheric pressure at sea level.

## Static Line Pressure

Static Line Pressure is the total pressure present at a particular point along a pressurised pipe.

## at – Technical Atmosphere Pressure Unit

Technical Atmosphere is used to represent a pressure value in multiples of atmospheric pressure.

## Pressure

Pressure is the amount of force applied to a unit area and is calculated by dividing the applied force by the area of the contact surface.

## Primary Pressure Reference Standard

Primary pressure reference standards are used to measure and generate pressures to a high level of accuracy and repeatability for calibration purposes.

## tsi – Tons per Square Inch (UK, Long) Pressure Unit

Tons or Tons Force per Square Inch (UK, Long) is a very large pressure unit used historically for measuring extremely high pressures.

## tsi – Tons per Square Inch (USA, Short) Pressure Unit

Tons or Tons Force per Square Inch (USA, Short) is 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. This is the American version of tons per square inch which uses the so called short ton that is […]

## Torr Pressure Unit

Torr is a pressure unit which is defined as 1 standard atmosphere divided by 760 (1 atm/760 or 101325 Pa/760).

## Vented Cable

Vented Cable has a vent tube running through the inside of the cable to provide a vent path between the electrical connections at either end.

## Water Density

The density of fresh water at a temperature of approximately 4 degrees Celsius is 1000 kg/m3.

## Wet/Dry

Wet/Dry describes a dp measurement device for use with a liquid on the positive pressure side and a dry/non-condensing gas on the negative pressure side.

## TSS – Thermal Span or Sensitivity Shift

Thermal Span or Sensitivity Shift signifies the maximum amount of span that will change at any measurement point within the compensated temperature range.

## Wet/Wet

Wet/Wet describes a differential pressure measurement device which is compatible with liquid on both the positive and negative side process connections.

## Wheatstone Bridge Strain Gauge

Wheatstone bridge strain gauge circuits are used extensively inside transducer to convert a mechanical strain into an electrical output signal.

## Span Offset

Span Offset is the amount of deviation in output or reading from the exact value at a point within the measurement span.

## Zero Offset

Zero Offset is the amount of deviation in output or reading from the exact value at the lowest point of the measurement range.

## Span

Span is the difference between the lowest and the actual reading or output signal of a measurement device.

## Zero Tare

Zero Tare is the operation of removing a zero offset to help obtain the optimal measurement over the whole measurement range.

## Span Sensitivity

Span Sensitivity defines the output signal characteristic of a strain gauge based sensor independent of measurement range or supply voltage.

## Square Root Extraction

Square Root Extraction is a mathematical process which is applied to a linear measurement scale to convert it to a non-linear square root scale.

## TEB – Total Error Band

Total Error Band (TEB) is the difference between the most negative and most positive deviation from the true measurement, determined from the combination of all known errors for a sensing device, within the constraints of the measurement and operating temperature range. Typically in the case of a pressure measurement device for example, the total error […]

## Transmitter

Transmitter (Tx) is a device which converts a sensor output into an analogue signal suitable for sending over long distances without significant signal loss or interference. A common type of sensor transmitter signal is a 4 to 20 milliamp current loop output.

## Turndown Ratio

Turndown Ratio describes the difference between the highest and lowest possible span of measurement output which can be set for a sensing device with a rangeable output signal such as 4 to 20mA output which is HART enabled.

## 2 Wire

2 wire is used to distinguish electrical connections for measurement signals which use only two connections for carrying both the power supply and signal.

## 4 to 20 mA Current Loop Output Signal

4-20mA Current loop output is a type of electrical signal that is used in a series circuit to provide a robust measurement signal.

## 3 Wire

3 wire is used to describe a type of electrical connection for a measurement signal which has only three connections for the power supply and signal output

## Wetted Parts

Wetted Parts are the measurement side components of a sensing device which are in contact with the liquid media to be measured.

## UKAS Calibration Certificate

UKAS Calibration Certificate is a formal document that details the procedure and results for a calibration completed by a UKAS certified calibration laboratory.