Sensors and Detectors – Process Measurement Flashcards

Comprehensive vocabulary flashcards covering sensors, detectors, and process measurement principles for nuclear plant operations based on the OP-BNT-CP02BP lecture notes.

Detector

A device whose physical characteristics change in response to a change in a process parameter.

Transducer

A device that converts the physical change of a detector into a usable form for display and control, typically an electrical voltage, current, or air signal.

Transmitter

A device that houses both a detector and a transducer together, allowing for remote operation and providing adjustments for zero and span.

Liquid-In-Glass Thermometer

A simple temperature-measuring device that utilizes the volumetric expansion and contraction of a liquid, such as mercury or alcohol, within a glass capillary tube.

Filled-System Thermometer

A device that provides temperature measurement at a distance using a bulb filled with gas or liquid connected to a receiving element, such as a Bourdon tube, by capillary tubing.

Bimetallic Strip Thermometer

A temperature detector made of two metals with different coefficients of thermal expansion fastened together, causing the strip to bend as temperature changes.

Coefficient of Linear Expansion

The quantity that describes how much an object will increase in length when it is heated $1^\circ C$.

Optical Pyrometer

A non-contact, usually hand-held device that measures the radiant energy and brightness of a surface to determine temperatures, typically greater than $1300^\circ F$.

Thermocouple

A temperature sensor composed of two wires of dissimilar metals joined at a sensing junction that develops an Electromotive Force (EMF) based on the temperature difference between the sensing and reference junctions.

Sensing Junction (Hot Junction)

The end of a thermocouple where the two dissimilar metal wires are joined and placed at the location to be measured.

Reference Junction (Cold Junction)

The point in a thermocouple circuit where the thermocouple wires are connected to copper wires, typically maintained at a constant temperature to ensure measurement accuracy.

Resistance Temperature Detector (RTD)

A sensor that operates on the principle that the electrical resistance of a metal, such as platinum, changes proportionally as its temperature changes.

Temperature Coefficient of Resistance

The fractional change in electrical resistance per unit change in temperature for a specific material.

Wheatstone Bridge

A common electrical circuit used for resistance temperature measurement, employing a DC power supply to detect voltage differentials across a measuring circuit leg containing an RTD.

Mercury Barometer

An instrument consisting of an inverted glass tube in a dish of mercury used to measure atmospheric pressure by the height of the mercury column.

Manometer

A direct pressure sensor consisting of a transparent tube containing liquid, such as water or mercury, where pressure changes cause a measurable displacement of the liquid column.

Bourdon Tube

A pressure element consisting of a flattened thin-walled tube bent into an arc that tends to straighten when pressurized, moving a pointer mechanism.

Bellows Pressure Element

A collapsible, seamless metallic unit with deep folds that is more sensitive to low pressures than a Bourdon tube and provides greater power for actuating mechanisms.

Diaphragm Pressure Element

A pressure-sensing device consisting of a metal disc in a housing that distorts under pressure, with the deflection transmitted to a gauge dial.

Differential Pressure (D/P) Cell

An instrument that measures the difference between two applied pressures, often used for determining flow, pressure, or liquid level.

Equalizing Valve

A valve that connects both the low-pressure and high-pressure sides of a D/P cell to equalize pressures and prevent over-ranging the element during isolation or return to service.

Open Vessel Level Detector

A level measurement application where the high-pressure side of a D/P transmitter is connected to the tank and the low-pressure side is vented to the atmosphere.

Dry Reference Leg

A level measurement setup for closed tanks where the low-pressure connection is filled with gas or vapor and kept dry to prevent liquid head pressure on that side.

Wet Reference Leg

A level measurement setup where the reference leg is filled with liquid to provide a known constant hydrostatic head, often used for tanks containing condensable fluids like steam.

Reference Leg Flashing

The rapid conversion of reference leg water to steam due to a pressure decrease below saturation, resulting in an indicated level higher than actual.

Dipstick

A direct level measurement method involving a calibrated scale placed in a fluid to determine the height of the wetted portion.

Gage Glass

A pressure-tight glass tube connected to a tank that allows the liquid level to be read directly as it seeks the same height as the fluid in the tank.

Electric Probe

A level measurement device that uses the ability of a liquid to conduct electricity between electrodes to signal when a specific level is reached.

Bubbler Device

An indirect level measurement method that uses a regulated air supply to measure the backpressure required to overcome the hydrostatic head of a liquid in a tank.

Mass Flowrate

The quantity of material in units of pounds mass flowing past a point at a given instant, expressed as $\text{lbm/hr}$ or $\text{lbm/sec}$.

Volumetric Flowrate

The volume of material flowing past a point per unit of time, normally expressed in gallons per minute ($gpm$) for liquids.

Head Flow Meter

A flow measurement device that operates by placing a restriction in the flow path to create a pressure drop proportional to the square of the flow rate.

Square Root Extractor

A circuit that converts a differential pressure signal into a linear flow signal by performing a square root operation, based on the relationship $\dot{V} \propto \sqrt{D/P}$.

Orifice Plate

A thin metal plate with a sharp-edged hole used as a flow restriction, characterized by high unrecoverable pressure loss.

Vena Contracta

The point downstream from an orifice plate where the flowing stream has its greatest convergence and maximum velocity.

Venturi Tube

A streamlined flow detector with a converging inlet, cylindrical throat, and diverging recovery cone, offering high accuracy and low permanent pressure loss.

Flow Nozzle

A flow measuring device with a streamlined contour used for high-velocity flows, more resistant to erosion and solids than an orifice plate.

Rotameter

A variable area flow meter consisting of a tapered tube and a float that rises to a height proportional to the flow rate.

Positive Displacement Meter

A device used for total flow measurement that operates by counting the number of times a chamber of known volume is filled and discharged.

Ultrasonic Flowmeter

A sensor that measures fluid velocity by detecting the frequency shift (Doppler effect) or transmission time differences of sonic pulses diagonally across a pipe.

Thermal Switch

A flow switch that uses a heater probe and RTDs to detect flow or no-flow conditions based on thermal dissipation in a medium.

Flow Totalizer

A device that calculates and accumulates total flow over time by integrating the flow rate signal from a primary measuring device.

Potentiometer

A position detector involving a slide wire attached to a valve stem that changes resistance to provide a feedback signal proportional to the valve's position.

Limit Switch

A device that provides position indication by mechanically closing or opening an electrical path at specific points of travel.

Reed Switch

A position indicator using flexible ferrous strips that close when approached by a permanent magnet attached to a moving component.

Linear Variable Differential Transformer (LVDT)

A highly accurate position detector that uses magnetic coupling between primary and secondary coils and a movable core to produce a signal proportional to displacement.

Torque Switch

A switch used in motor-operated valves to control the amount of force applied, turning off the motor when a specific torque limit is reached.

Loop Seal

A U-shaped water leg that separates two regions at different pressures while allowing water to be drained from one to the other.

Strain Gauge

A pressure transducer based on the principle that the electrical resistance of a conductor changes as its shape is deformed by applied pressure.

Piezoelectric Crystal

A transducer component that produces an electric potential when elastically deformed, commonly used for measuring dynamic pressure or vibration.

Live Zero

A signal transmission convention where a minimum scale reading is represented by a non-zero signal (such as $4\,ma$), allowing for the identification of a broken wire or lost signal.

Flapper-Nozzle Unit

A basic pneumatic system that converts small mechanical motion into a $3-15\,psig$ output air signal by varying the restriction at a nozzle.

Relay Valve

A pneumatic device that acts as a mechanical amplifier, converting small mechanical motion into an output signal faster than a simple flapper-nozzle.

Proportional Feedback Device

A pneumatic signal device that incorporates a feedback bellows to provide negative feedback, stabilizing and smoothing the output signal relative to the measured parameter.