Reference

Instrumentation & Automation Glossary

108 terms that turn up on datasheets, specifications and enquiries — pressure and temperature measurement, flow, level, valves, drives, signals and hazardous-area certification. Written plainly, for engineers specifying equipment for Gulf conditions.

108 terms

3

316L Stainless SteelMaterials & Connections: The default industrial stainless steel, with molybdenum for improved resistance to chlorides and pitting. The L denotes low carbon, which resists sensitisation at welds.Related:Pressure Transmitters

4

4–20 mA LoopSignals & Accuracy: The standard analogue process signal, where current rather than voltage carries the value so cable resistance does not affect the reading. A live zero of 4 mA distinguishes a genuine zero measurement from a broken wire.Related:Pressure Transmitters Temperature Sensors

A

Absolute PressurePressure: Pressure measured against a perfect vacuum as the zero reference. Written as bara or psia. Used where readings must be independent of local barometric pressure, such as vacuum processes and vapour pressure measurement.Related:Pressure Transmitters
AccuracySignals & Accuracy: How close a reading is to the true value, usually stated as a percentage of full scale or of reading. A percentage of full scale becomes a large relative error at the bottom of the range — which is why turndown matters.Related:Pressure Transmitters
Adjustable DifferentialPressure: On a switch, the ability to set the gap between the switching point and the reset point. Set wide enough to stop the contacts chattering on a process that hovers near setpoint.Related:Pressure Switches Temperature Switches
ATEXHazardous Area & Certification: The European framework for equipment used in explosive atmospheres, under Directive 2014/34/EU. ATEX marking is mandatory in the EU and widely specified elsewhere, including across the Gulf.Related:Pressure Transmitters Temperature Sensors Electric Motors

B

Burst PressurePressure: The pressure at which the sensing element physically fails and loses containment. Always well above the rated range, and never a working limit.Related:Pressure Transmitters

C

CalibrationSignals & Accuracy: Comparing an instrument against a traceable reference and, where necessary, adjusting it. Calibration is the comparison; adjustment is what follows if the error is out of tolerance.Related:Pressure Transmitters
CavitationValves & Actuators: The formation and violent collapse of vapour bubbles where local pressure falls below the liquid's vapour pressure, typically downstream of a throttling valve. Causes noise, vibration and rapid erosion of trim.Related:Industrial / Process Valves
Chemical SealPressure: A flexible diaphragm assembly, filled with a transmitting fluid, that isolates an instrument from the process. Used for corrosive, viscous, crystallising or high-temperature media where the sensor cannot contact the process directly.Related:Pressure Transmitters
Cold Junction CompensationTemperature: Correction applied for the temperature at the point where a thermocouple connects to the measuring instrument. Without it, a thermocouple reading drifts with the temperature of its own terminals.Related:Temperature Sensors
Compound PressurePressure: A range spanning both vacuum and positive pressure, for example −1 to 10 bar. Specified where a process can swing below atmospheric, such as pump suction lines.Related:Pressure Transmitters
Coriolis Flow MeterFlow: A meter that measures true mass flow directly from the twist induced in vibrating tubes by the flowing fluid, and reports density as a by-product. The most accurate common technology, and the most expensive.Related:Flow Meters
Custody TransferFlow: Measurement on which a commercial transaction is based, where the reading determines what is invoiced. Demands higher accuracy, traceable calibration and, usually, regulatory approval of the metering system.Related:Flow Meters
Cv and KvValves & Actuators: Flow coefficients expressing valve capacity. Cv is the flow in US gallons per minute of water at 1 psi drop; Kv is the metric equivalent in m³/h at 1 bar drop. Used to size a valve against required flow.Related:Solenoid Valves Industrial / Process Valves

D

DeadbandSignals & Accuracy: A range of input over which the output does not change. Deliberately applied to switches and controllers to prevent rapid cycling around setpoint.Related:Pressure Switches Temperature Switches Flow Switches
Differential PressurePressure: The difference between two applied pressures, measured by a single instrument with high and low ports. The basis of orifice flow measurement, filter monitoring and level measurement in closed vessels.Related:Pressure Transmitters Flow Meters Level Measurement
DriftSignals & Accuracy: Gradual change in output over time or with temperature, with the input unchanged. Long-term drift determines how often an instrument must be recalibrated.Related:Pressure Transmitters
Duplex and Super DuplexMaterials & Connections: Stainless steels with a mixed austenitic-ferritic structure, giving roughly twice the strength of 316L with better chloride and stress-corrosion resistance. Widely used in seawater and desalination plant.Related:Pressure Transmitters Industrial / Process Valves
Duty Cycle (S1–S9)Motors & Drives: IEC classification of a motor's loading pattern over time. S1 is continuous running; other classes cover intermittent, short-time and frequently starting duties, each affecting permissible output.Related:Electric Motors

E

Electromagnetic Flow MeterFlow: A meter that applies a magnetic field across the pipe and measures the voltage induced by the moving liquid, following Faraday's law. Requires an electrically conductive liquid; offers no obstruction and no pressure drop.Related:Flow Meters
EncoderMotors & Drives: A sensor that converts shaft rotation into an electrical signal for position or speed feedback. Incremental types output pulses and must be homed after power loss; absolute types report true position at all times.Related:Encoders & Resolvers
EPDMMaterials & Connections: An elastomer well suited to water, steam and brake fluid, and the usual choice for potable water duty. Attacked by mineral oils and fuels.Related:Solenoid Valves Industrial / Process Valves
Ex d (Flameproof)Hazardous Area & Certification: A protection method in which the enclosure is strong enough to contain an internal explosion and cool escaping gases through defined flamepaths, so surrounding atmosphere is not ignited. Robust, and heavy.Related:Electric Motors Pressure Transmitters
Ex e (Increased Safety)Hazardous Area & Certification: Protection using enhanced construction — larger creepage distances, better terminations, tighter temperature control — so that arcs and hot surfaces do not occur in normal operation.Related:Electric Motors
Ex ia / Ex ib (Intrinsic Safety)Hazardous Area & Certification: Protection that limits electrical and thermal energy in the circuit below what can ignite the atmosphere, rather than containing an explosion. Ex ia is permitted in Zone 0. Allows live working and maintenance in the hazardous area.Related:Pressure Transmitters Temperature Sensors

F

Fail-Safe PositionValves & Actuators: The position an actuated valve moves to when power or air is lost, driven by a spring. Specified as fail-closed, fail-open or fail-in-place according to which condition is safe for the process.Related:Valve Actuators Industrial / Process Valves
Flame ArrestorValves & Actuators: A passive device with narrow passages that quench a flame front, allowing gas to pass while preventing flame propagation into a tank or pipeline. Sized for the specific gas group it must stop.Related:Flame Arrestors
Flange Rating (ANSI Class / PN)Materials & Connections: Pressure-temperature classification of flanged joints. ANSI/ASME uses Class 150, 300, 600 and upward; the European PN system rates in bar. A class rating falls as temperature rises.Related:Industrial / Process Valves

G

Galvanic IsolationSignals & Accuracy: Separating circuits so no direct conduction path exists between them, while the signal still passes. Prevents earth loops and protects equipment from surges on long field cabling.Related:PLCs
Gas GroupHazardous Area & Certification: Classification of gases by how easily they ignite and how readily flame passes through a gap: IIA (propane), IIB (ethylene), IIC (hydrogen and acetylene, the most demanding). Equipment certified for IIC covers the groups below it.Related:Pressure Transmitters Electric Motors
Gauge PressurePressure: Pressure measured relative to the surrounding atmospheric pressure, so it reads zero at ambient. Written as barg or psig. The most common reference for process measurement.Related:Pressure Transmitters
Guided Wave RadarLevel: Radar level measurement in which the pulse travels down a probe rather than through open space, concentrating the signal. Handles foam, turbulence, narrow vessels and low-reflectivity media better than free-space radar.Related:Level Measurement

H

Harmonics and THDMotors & Drives: Distortion of the supply waveform drawn by non-linear loads such as drives, expressed as total harmonic distortion. Excessive harmonics overheat transformers and cables and may breach the site's supply agreement.Related:Drives (VFD)
HARTAutomation & Control: A digital signal superimposed on a conventional 4–20 mA loop, allowing configuration, diagnostics and additional variables to be read without disturbing the analogue measurement. Lets one cable carry both.Related:Pressure Transmitters Temperature Sensors Level Measurement
Hastelloy C276Materials & Connections: A nickel-molybdenum-chromium alloy with excellent resistance to strong acids, chlorides and sour service. Specified where 316L would corrode, at considerably higher cost.Related:Pressure Transmitters
Hazardous Area ZonesHazardous Area & Certification: Classification by how often an explosive atmosphere is present. For gases: Zone 0 continuously, Zone 1 occasionally in normal operation, Zone 2 rarely and briefly. Zones 20, 21 and 22 are the dust equivalents.Related:Pressure Transmitters Electric Motors
Head TransmitterTemperature: A small transmitter mounted inside the sensor's connection head, converting the RTD or thermocouple signal to 4–20 mA or a digital output at the sensor. Removes long runs of sensitive sensor cable and the errors they collect.Related:Temperature Sensors
HMI (Human Machine Interface)Automation & Control: The operator's screen onto a machine or process, showing status and accepting commands. Distinct from SCADA, which supervises and records across many units rather than operating one.Related:HMIs
HTL and TTL OutputMotors & Drives: Two encoder signal standards. TTL (RS-422 line driver) is 5 V and differential, suited to long cable runs with good noise immunity; HTL (push-pull) uses 10–30 V and is more robust in electrically noisy plant.Related:Encoders & Resolvers
HydrastepLevel: An electrode-based system that distinguishes water from steam in a boiler drum by conductivity, giving a stepped indication of drum level. Widely used for boiler water level safety duty in power generation.Related:Boiler Water Level Controls
HydratectLevel: A water and steam detection system used for boiler protection and drum level alarm, based on conductivity probes and associated electronics.Related:Boiler Water Level Controls
Hydrostatic Level MeasurementLevel: Inferring level from the pressure exerted by the liquid column above the sensor. Simple and robust, but the reading depends on the density of the medium, so it shifts if the product changes.Related:Level Measurement Pressure Transmitters
HysteresisSignals & Accuracy: The difference in reading at a given point depending on whether the input is rising or falling. Arises from mechanical and magnetic effects within the sensing element.Related:Pressure Transmitters Pressure Switches

I

IE Efficiency ClassMotors & Drives: The international efficiency rating for electric motors under IEC 60034-30-1, running from IE1 to IE5, with higher numbers more efficient. Many markets now mandate a minimum class for new installations.Related:Electric Motors
IECExHazardous Area & Certification: The international certification scheme for equipment in explosive atmospheres, based on the IEC 60079 standards. Widely accepted across the GCC and often specified alongside ATEX.Related:Pressure Transmitters Electric Motors
IEPE AccelerometerMotors & Drives: A vibration sensor with built-in charge amplifier powered by a constant current over the same two wires that carry the signal. The industrial standard for permanent vibration monitoring.Related:Vibration Monitoring
Insulation ClassMotors & Drives: The maximum temperature a motor's winding insulation can tolerate — Class B 130 °C, F 155 °C, H 180 °C. In high ambient conditions a motor is often specified with Class F insulation but limited to Class B temperature rise, leaving thermal margin.Related:Electric Motors
Interface LevelLevel: The boundary between two immiscible liquids of different density, such as oil sitting above water in a separator. Measuring it requires a technology that can distinguish the two layers, not just the top surface.Related:Level Measurement
IO-LinkAutomation & Control: A point-to-point digital link between a controller and individual sensors or actuators over standard unshielded cable, carrying process data plus parameters and diagnostics. Simplifies sensor replacement, as settings download automatically.Related:PLCs
IP RatingHazardous Area & Certification: Ingress protection to IEC 60529. The first digit rates solids, the second liquids — IP66 withstands powerful water jets, IP68 continuous immersion, IP69K high-pressure high-temperature washdown.Related:Pressure Transmitters Electric Motors

L

Limit SwitchValves & Actuators: An electromechanical switch operated by physical contact with a moving part, used to confirm position or end of travel. Heavy-duty types are built for high cycle counts, impact and harsh environments.Related:Heavy-Duty Limit Switches
LinearitySignals & Accuracy: How closely the instrument's response follows a straight line between zero and full scale, quoted as the maximum deviation from that line.Related:Pressure Transmitters

M

Modbus RTU and Modbus TCPAutomation & Control: A long-established open protocol. RTU is serial, usually over RS-485; TCP carries the same register model over Ethernet. Simple, universally supported, and still the common denominator between equipment from different vendors.Related:PLCs HMIs Drives (VFD)
MonelMaterials & Connections: A nickel-copper alloy resistant to seawater, hydrofluoric acid and alkalis. Common in desalination and marine service.Related:Pressure Transmitters

N

NACE MR0175 / ISO 15156Hazardous Area & Certification: The standard governing material selection for equipment exposed to wet hydrogen sulphide, where susceptible metals crack. Routinely specified on sour service in Gulf oil and gas, and it constrains which materials may be used.Related:Pressure Transmitters Industrial / Process Valves
NAMUR SensorSignals & Accuracy: A two-wire proximity sensor to EN 60947-5-6 whose current changes between defined levels, allowing the connected amplifier to detect wire break and short circuit as well as the switching state.Related:Speed & Rotation Sensors
NEMA RatingHazardous Area & Certification: The North American enclosure classification, covering environmental protection much as IP does but also addressing corrosion and icing. NEMA 4X denotes watertight and corrosion-resistant.Related:Heavy-Duty Limit Switches
Nitrile (NBR / Buna-N)Materials & Connections: A general-purpose elastomer with good resistance to oils and fuels at moderate temperature. The commonest and cheapest seal material, but limited on temperature and poor with ozone.Related:Solenoid Valves
Normally Open and Normally ClosedValves & Actuators: The valve or contact position with no power applied. Chosen so that a power failure drives the process to its safe state.Related:Solenoid Valves Heavy-Duty Limit Switches
NPT and BSP ThreadsMaterials & Connections: The two dominant pipe thread standards. NPT is tapered with a 60° form and seals on the threads; BSP comes parallel (G) sealing on a face or bonded washer, and tapered (R) sealing on the threads. They are not interchangeable.Related:Pressure Transmitters

O

Orifice PlateFlow: A machined restriction that creates a pressure drop proportional to the square of flow rate, read by a DP transmitter. Long established and inexpensive, at the cost of permanent pressure loss and limited turndown.Related:Flow Meters Pressure Transmitters
Oval Gear Flow MeterFlow: A positive displacement meter that counts discrete volumes carried between meshing oval rotors. Handles viscous liquids such as oils well, where velocity-based meters struggle.Related:Flow Meters
OverpressurePressure: The maximum pressure an instrument can withstand without permanent change to its performance. Exceeding it may not burst the sensor but can shift the zero point beyond specification.Related:Pressure Transmitters Pressure Switches

P

PID ControlAutomation & Control: A control algorithm combining proportional, integral and derivative response to drive a process variable to setpoint. The proportional term responds to present error, the integral to accumulated error, the derivative to rate of change.Related:PLCs
PLC (Programmable Logic Controller)Automation & Control: An industrial controller that reads inputs, executes a stored program cyclically and drives outputs. Built for deterministic scanning and continuous operation in plant conditions.Related:PLCs
PROFIBUS and PROFINETAutomation & Control: PROFIBUS is a serial fieldbus for connecting controllers to distributed I/O and instruments; PROFINET is its Ethernet-based successor, supporting higher speed and standard network infrastructure.Related:PLCs Drives (VFD)
Proof PressurePressure: The pressure an instrument can be subjected to and still return to its specified accuracy once the pressure is removed.Related:Pressure Transmitters
Pt100Temperature: The most widely used RTD, a platinum element measuring 100 ohms at 0 °C, defined by IEC 60751. Pt1000 is the same curve scaled to 1000 ohms, which reduces the effect of lead resistance.Related:Temperature Sensors
PTFEMaterials & Connections: A fluoropolymer that is chemically inert to almost everything and usable across a wide temperature range. Used for seats, seals and diaphragm coatings; it cold-flows under sustained load.Related:Industrial / Process Valves Solenoid Valves

R

Radar Level MeasurementLevel: Non-contact level measurement using microwave pulses reflected from the product surface. Unaffected by density, pressure, temperature or vapour, which makes it suitable for difficult and changing media.Related:Level Measurement
Ratiometric OutputSignals & Accuracy: A voltage output expressed as a proportion of the supply voltage, typically 10–90%. Common in mobile hydraulics and automotive work, where it cancels the effect of a varying supply.Related:Pressure Transmitters
RepeatabilitySignals & Accuracy: How closely an instrument reproduces the same reading for the same input under unchanged conditions. For control purposes repeatability often matters more than absolute accuracy.Related:Pressure Transmitters
Resilient-Seated ValveValves & Actuators: A valve using an elastomeric seat to achieve bubble-tight shut-off without metal-to-metal contact. Common in butterfly valves for water and general service.Related:Industrial / Process Valves
ResolverMotors & Drives: A rugged electromagnetic position sensor with no electronics in the sensing element, giving absolute position within one revolution. Preferred over optical encoders where heat, shock and vibration are severe.Related:Encoders & Resolvers
Response Time (T90)Temperature: The time a sensor takes to register 90% of a step change in the measured value. Determined as much by the thermowell and its fit as by the sensing element itself.Related:Temperature Sensors
RTD (Resistance Temperature Detector)Temperature: A sensor whose electrical resistance rises predictably with temperature, most commonly platinum. More accurate and more stable than a thermocouple over moderate ranges, but with a narrower span and slower response.Related:Temperature Sensors

S

Safety Relief ValveValves & Actuators: A self-acting valve that opens at a set pressure to protect a vessel or system from overpressure, then reseats once pressure falls. The last line of mechanical protection, independent of any control system.Related:Safety Relief Valves
SCADAAutomation & Control: Supervisory control and data acquisition: a system that gathers data from distributed controllers, presents it centrally and archives it for analysis and reporting.Related:PLCs HMIs
Sealed Gauge PressurePressure: Pressure referenced to a fixed atmospheric pressure sealed inside the sensor at manufacture, rather than to live ambient. Common on higher ranges and submersible instruments where a vent to atmosphere is impractical.Related:Pressure Transmitters
SIL (Safety Integrity Level)Hazardous Area & Certification: A measure of the risk reduction a safety function provides, from SIL 1 to SIL 4, defined by IEC 61508 and applied to the process industries by IEC 61511. SIL applies to the whole safety loop, not to a single device in isolation.Related:Pressure Transmitters Safety Relief Valves
SiphonPressure: A coiled or U-shaped tube that traps condensate between hot steam and a pressure instrument, protecting the sensor from direct high temperature. Standard practice on steam service.Related:Pressure Transmitters Pressure Switches
SnubberPressure: A flow-restricting fitting installed ahead of a pressure instrument to damp pulsation and pressure spikes, typically on reciprocating pump and compressor discharge. Extends sensor life considerably on pulsating duty.Related:Pressure Transmitters Pressure Switches
Soft StarterMotors & Drives: A device that ramps voltage to limit inrush current and mechanical shock at motor start. Cheaper than a VFD where only starting is a problem and no running speed control is needed.Related:Drives (VFD)Electric Motors
Solenoid ValveValves & Actuators: A valve opened or closed by an electromagnetic coil acting on a plunger. Direct-acting types work at zero differential pressure; servo-assisted types use line pressure to shift the main seat and need a minimum differential.Related:Solenoid Valves
Span and ZeroSignals & Accuracy: Zero is the output at the lower range value; span is the difference between the upper and lower range values. Adjusting zero shifts the whole curve, while adjusting span changes its slope.Related:Pressure Transmitters
Static PressurePressure: The line pressure acting equally on both sides of a differential pressure instrument. A DP transmitter must be rated for the static pressure as well as the differential span it measures.Related:Pressure Transmitters
Straight RunFlow: The length of undisturbed straight pipe required upstream and downstream of a flow meter, expressed in pipe diameters. Insufficient straight run distorts the flow profile and is among the commonest causes of flow measurement error.Related:Flow Meters

T

Temperature Class (T1–T6)Hazardous Area & Certification: The maximum surface temperature equipment may reach, which must stay below the ignition temperature of the surrounding gas. T6 is the strictest at 85 °C, T1 the least at 450 °C.Related:Electric Motors Pressure Transmitters
ThermocoupleTemperature: A sensor made from two dissimilar metals joined at a measuring junction, generating a small voltage proportional to the temperature difference across it. Covers far wider temperature ranges than an RTD and responds faster, at lower accuracy.Related:Temperature Sensors
ThermowellTemperature: A closed-end tube that houses a temperature sensor and isolates it from the process, allowing the sensor to be replaced without breaking containment. Must be checked for wake frequency to avoid vibration-induced failure in fast-flowing lines.Related:Temperature Sensors
Three-Wire and Four-Wire RTDTemperature: Wiring schemes that cancel the resistance of the cable itself, which would otherwise read as extra temperature. Three-wire compensates approximately and suits most industrial work; four-wire eliminates the error entirely and is used for reference measurement.Related:Temperature Sensors
Tri-ClampMaterials & Connections: A hygienic connection using a gasket clamped between two ferrules, giving a crevice-free joint that can be dismantled for cleaning. Standard in food, beverage and pharmaceutical service.Related:Pressure Transmitters
Turbine Flow MeterFlow: A meter in which a rotor spins at a rate proportional to flow velocity, sensed magnetically. Accurate on clean, low-viscosity liquids; bearings wear and it tolerates dirt poorly.Related:Flow Meters
Turndown RatioFlow: The ratio of the maximum to the minimum flow an instrument can measure within its stated accuracy. A 10:1 turndown on a 100 m³/h meter means readings below 10 m³/h fall outside specification.Related:Flow Meters
Two-Wire and Four-Wire TransmittersSignals & Accuracy: A two-wire (loop-powered) transmitter draws its supply from the same pair that carries the signal, simplifying wiring. A four-wire device has a separate supply, permitting higher power and additional outputs.Related:Pressure Transmitters

U

Ultrasonic Flow MeterFlow: A meter that derives velocity from the difference in transit time of ultrasonic pulses sent with and against the flow. Available as clamp-on units that need no pipe penetration.Related:Flow Meters
Upper Range Limit (URL)Signals & Accuracy: The highest value an instrument can be calibrated to measure, as distinct from the range it is currently set to. Turndown is calculated from the URL.Related:Pressure Transmitters

V

Vacuum ContactorAutomation & Control: A switching device whose contacts open and close inside a sealed vacuum bottle, extinguishing the arc rapidly. Gives long electrical life on frequent motor switching duty at medium voltage.Related:Vacuum Contactors
Vector ControlMotors & Drives: A drive control method that regulates motor flux and torque independently, giving accurate speed and full torque at low speed. Contrasts with simpler V/f control, which suits fans and pumps.Related:Drives (VFD)
VFD (Variable Frequency Drive)Motors & Drives: A drive that varies motor speed by changing the frequency and voltage supplied to it. On pump and fan duty it typically saves substantial energy compared with throttling, because power varies with the cube of speed.Related:Drives (VFD)
Vibration MonitoringMotors & Drives: Measuring machine vibration to detect developing faults such as imbalance, misalignment and bearing wear before failure. ISO 10816 and ISO 20816 give severity limits by machine class.Related:Vibration Monitoring
Viton (FKM)Materials & Connections: A fluoroelastomer seal material with good resistance to oils, fuels and high temperature. Poor with steam, hot water and amines, where EPDM is the usual alternative.Related:Solenoid Valves
Vortex Flow MeterFlow: A meter that counts the vortices shed alternately behind a bluff body placed in the flow, whose frequency is proportional to velocity. Well suited to steam and to hot gas and liquid service.Related:Flow Meters

W

Water HammerValves & Actuators: A pressure surge caused by rapidly stopping a moving column of liquid, capable of damaging pipework, valves and instruments. Mitigated by slowing valve closure or fitting surge arrestors.Related:Solenoid Valves Industrial / Process Valves
Wet Leg and Dry LegLevel: Impulse line arrangements for measuring level in a closed pressurised vessel with a DP transmitter. A wet leg is deliberately filled with liquid and needs its constant head calibrated out; a dry leg is kept empty.Related:Level Measurement Pressure Transmitters
Wetted PartsMaterials & Connections: Every component of an instrument that contacts the process medium. The list that matters most for chemical compatibility — a suitable body is irrelevant if the seal or diaphragm is attacked.Related:Pressure Transmitters
Winding Protection SensorTemperature: A temperature sensor embedded in a motor or transformer winding to detect overheating before insulation is damaged. Usually a PTC thermistor, bimetallic switch or Pt100 element.Related:Temperature Sensors Electric Motors

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