Glossary of Terms


Every industry has its own terminology. The environmental water instrumentation industry is no different. This section contains a glossary of terms common to the industry.

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Accuracy

Ratio of error to full-scale output (+/- percent of FSO).  Static accuracy includes the effects of non-linearity, non-repeatability and hysteresis at room temperature.  Expressed as a percentage of FSO.  EX:  Accuracy………….25% FSO

Absolute Pressure

Pressure measured relative to a vacuum.  Usually expressed in Pounds per Square Inch Absolute (PSIA).  Absolute Pressure Transducers are calibrated to read true atmospheric pressure.  EX:  The Output of an absolute Pressure Transducer is approx. 14.69 PSI at sea level.

Bar

A unit of pressure, typically used in Europe, that is equal to 10 5 Newtons per square meter or .98697 standard atmosphere or 14.696 PSI.

Barometric Compensation

Method employed by a gauge type transducer in which the pressure readings are balanced against atmospheric (barometric) pressure to produce a barometrically compensated pressure reading.  Usually expressed in Pounds per Square Inch gauge (PSIG).  The vent tube in the cable provides the atmospheric pressure to the backside of the pressure Diaphragm.

Calibration

Process by which the output of a sensor element is matched with a specific pressure within the span of the pressure sensor.

Desiccant Package

Method of drying air prior to it entering into the vent tube of a pressure transducer.

Diaphragm

Thin stainless steel, corrugated piece of the pressure element that deforms with pressure and which is converted to an electrical output.

Dual Diaphragm

Type of pressure element employing a stainless steel primary diaphragm and a second silicon diaphragm separated by an oil (Oil-filled diaphragm) and sealed.  This is the type of diaphragm used in INW Pressure Transducers.

Drift

A change in a given output characteristic over time at a specific reference temperature.

Excitation

The required input voltage to operate the device (Pressure Transducer).  EX:  Excitation……………12 Volts

Full Scale Output

The algebraic difference between endpoints.  One endpoint is the actual offset voltage and the other endpoint is the upper limit of the range.  This term is often used synonymously with Span.

Gauge

The differential pressure measured with respect to atmospheric pressure.  Gauge pressure is measured by routing a vent tube (provided in vented transducer cables) from the backside of the pressure element to the atmosphere.  Pressure measurement in gauge type sensors provide only the net pressure of the medium by compensating for atmospheric pressure changes.  This is the most common type of transducer that INW makes.

Hysteresis

The maximum difference in the Output Signal, at a given pressure, when first approached with increasing and then decreasing pressure.  Typically, errors associated with non-linearity, non-repeatability and hysteresis are grouped together in one specification.  EX:  Hysteresis………………… .50%

Linearity

The degree to which the output characteristic tracks a specified straight line over the rated pressure range.  Typically, errors associated with non-linearity, non-repeatability and hysteresis are grouped together in one specification.  Usually expressed in percent of FSO.  EX:  Linearity………………… .1%FSO

mBar

A unit of measure, typically used in Europe, that is 1/1000 of a Bar or .00098697 standard atmosphere or .01450 PSI.

milli-Amp (mA)

1/1000 of one Amp.  Common output of PS9800 and PS98i pressure transducers.

millie-Volt (mV)

1/1000 of a Volt.  Common output of PS9805 pressure transducer.

Non-vented Cable

Pressure transducer cable containing no vent tube.  Used primarily for absolute and sealed gauge pressure transducer applications, however, also used in the manufacture of extension cables for AquiStar Systems.

Output Signal

Electrical signal, milliAmps or milliVolts, produced by the pressure transducer that corresponds to a specific pressure and is measured by electrical measuring equipment.  EX:  4-20mA, 0-50 mV

Over Pressure

Pressure applied to the transducer which is beyond the limit of the calibrated pressure range.  EX:  a pressure of 15.1 PSI applied to a Pressure Transducer with a Range of 15 PSI.  Also referred to as proof pressure.

Pressure

Force applied over a surface, measured as force per unit of area.  EX:  Pounds per Square Inch (PSI).

Pressure Element

Device used to convert fluid pressure into an electrical signal in INW pressure transducers.  This is the key component of all INW pressure sensors.

Pressure Range (Range)

Term used to describe the full-scale output of the pressure transducer or pressure transmitter.  Range is expressed in PSI.  EX:  30 PSI

Pressure Transmitter

Term applied to pressure sensors which incorporated active signal conditioning of the bridge output to provide a high level signal to data acquisition systems.  EX:  A 4-20 milliAmp output transducer (PS9800).

PSI

Pounds per Square Inch.  Typical engineering units describing pressure measurements in the United States.  EX:  15 PSI described 15 Pounds per Square Inch.

Repeatability

The ability of a device to reproduce an output reading at the reference temperature when a given pressure is applied.  EX:  Comparing the output at 50% of Full Scale pressure on consecutive upward pressure sweeps from 0-100% would yield the Repeatability of the device.  Repeatability is expressed as a percentage of Full Scale.  Non-Repeatability of a device is usually expressed, along with non-linearity and hysteresis, as the static accuracy in percent FSO.  EX’s:  Repeatability………… .1% FSO.

Resistance

The tendency of a conductor to oppose the flow of current, causing electrical energy to be changed into heat.  EX:  The conductors in the pressure transducer cable.

Resolution

The size of the discrete step change in the output signal as the pressure is continuously varied.  INW PS-9XXX transducers provide an analog (continuous) a output signal and thus have infinite resolution.

Sealed Gauge

Similar to an absolute pressure sensor only sealed gauge sensor is calibrated to be “0 PSI” pressure in ambient atmospheric pressure.  Sealed gauge transducers do not compensate for changes in atmospheric pressure.

Span

Full scale output, (Volts or Amps) minus the Offset (Volts or Amps).  A PS9800 pressure transmitter, with an output of 4-20mA, has a span of 16mA.

Transducer

Term generally applied to sensors, which do not incorporate active signal conditioning of the bridge output.  The output signal is derived directly from the bridge outputs; however, this is not meant to imply that no active circuitry is present.

Transmitter

Term applied to sensors which incorporate active signal conditioning of the bridge output to provide a high level signal to data acquisition systems.

Vent Tube

Nylon tube running the length of the cables that allow changes in atmospheric pressure to compensate the pressure readings in gauge type sensors.

Warm-up Time

Time required for the device to stabilize to a specified value following the application of the specified excitation.

Zero Offset

Output of a device at a specified temperature with zero pressure applied.