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Flashcards in Chapter 12 Deck (71):
1

  • measure a range of input condition and generate a range of output values

Analog Sensors

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resistance temperature detectors and thermistors

Resistance as a function of temperature

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thermocouples and solid state temperature sensors

Voltage as a function of temperature

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a temperature-sensing device that detects a change in the resistance of a metal as a function of temperature

Resistance temperature detector (RTD)  

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are electronic components that exhibit a large change in resistance with a change in the device temperature.

Thermistors

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Exhibit decreasing electrical resistance with increases in environmental temperature and increasing electrical resistance with decreases in environmental temperature, and PTC thermistors exhibit increasing electrical resistance with increases in environmental temperature and decreasing electrical resistance with decreases in environmental temperature

NTC thermistors

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are temperature-sensing devices that produce a small voltage in the millivolt range as a function of temperature. Thermocouples are constructed using two dissimilar metal wires, 

Thermocouples

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integrated circuits (ICs) whose output is linearly proportional to a temperature scale, typically Celsius

Solid-state temperature sensors

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devices that detect the force exerted by one object on another.

Pressure sensors

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______________is defined as the amount of force applied to an area, where pressure in expressed in pounds per square inch (psi). Pressure in liquids and gases is referred to as hydraulic pressure, the change in an object’s shape when force is applied is called stress or strain.

Pressure

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pressure is a function of the amount of deformation of an object.

Direct pressure sensors

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Direct pressure sensors measure strain, which is

the amount of deformation of a body due to an applied pressure or force.

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pressure is a function of the amount of deflection of an object

Deflection pressure sensors

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pressure is a function of the difference in two measurements

Differential pressure sensors

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pressure is a function of the deformation/deflection of a crystal or electronic component.

Piezoelectric and solid-state sensors

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Piezoelectric pressure sensors operate 

The piezoelectric effect occurs

when pressure is applied to a crystal; the crystal deforms and produces a small voltage, which is proportional to the deformation.

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Solid-state sensors derive measurements

They differ from electromechanical sensors in that rather

than consisting of several discrete components, these sensors have all their electrical and mechanical components built into a single piece of silicon. A small deflection of the diaphragm causes implanted resistors to exhibit a change in ohmic value. The sensor converts this change into a voltage that can be easily interpreted as a continuous and linear pressure reading.

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Flow Sensors

  • The measurement of flow rate indicates how much fluid is used or distributed in a process and it is frequently used as control variable, which aids in maintaining the efficiency of a process.

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those sensors that disturb the flow of the fluid that they are measuring.

Intrusive

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those sensors that do not disturb the flow of the fluid that they are measuring

Non-intrusive

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fluid flows rather smoothly parallel to the walls of the pipe.

Laminar flow

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fluid flows down the pipe, but swirls within the flow

Turbulent flow

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measurement methods of flow

the flow rate is determined by calculating the pressure difference (or pressure drop) as the fluid flows through an obstruction such as an orifice plate

Differential

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measurement methods of flow

the flow rate is determined based on the velocity of the fluid as it passes through a turbine.

Velocity

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measurement methods of flow

the flow rate is determined by measuring all the fluid used.

Displacement

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measurement methods of flow

the flow rate is determined based on the total volume of the fluid that passes through the sensor.

Mass

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measurement methods of flow

the flow rate is determined by a visual reading of a graduated scale

Visual

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Flow sensing from differential pressure (or pressure drop)

is based on the fact that the difference in the pressure measurements on both sides of physical restriction in the flow of a fluid is proportional to the square of the flow rate.

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Q image thumb

Orifice plate

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Venturi

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Pitot tube

 

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Flow Nozzle

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Elbow

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Paddle wheel flow

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Turbine flow

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Vortex Flow

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Electromagnetic Flow

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Ultrasonic flow

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Thermal mass flow

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Coriolis flow 

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Visual flow 

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  • An____________ is a washer- shaped device that is installed in a piping sys- tem, and the flow rate is determined from the measurements of pressure in front of and behind the plate.

orifice plate

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A __________is a flow-measuring device that consists of a gradual contraction followed by a gradual expansion within a fluid- carrying pipe.

venturi

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A___________ is a flow-measuring device consisting of two tubes placed in the fluid flow that sense two pressures—impact pressure and static pressure.

pitot tube

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A___________ is a narrowing spout installed inside a piping system to obtain a pressure differential.

flow nozzle

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An existing__________  in the piping system can be used to obtain a differential pressure

elbow

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This flow sensor is installed in a pipe so that the flowing fluid causes its paddlewheel to rotate.

Paddlewheel flow sensor

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Turbine flow sensor

a fluid moves through a pipe and strikes the vanes of a turbine, the turbine will start to spin and rotate

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Vortex flow sensor

The vortex flow sensor includes a non-streamlined object (a bluff body) placed in the fluid flow, which creates vortices (whirlpools or eddies) in a downstream flow

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Electromagnetic flow sensor

The electromagnetic flow sensor measures the electrical charges in flowing fluid, which are proportional to the fluid velocity

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Ultrasonic flow sensor:

The operation of the ultrasonic flow sensor is based on the motion of a sound source and its effect on the frequency of the sound.

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The________________________ measures fluid flow by precision- fitted rotors as flow-measuring elements where known or fixed volumes are displaced between the rotors

displacement flow sensor

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the fluid flowing through the piston is a known quantity, thus the flow rate is a function of the number of piston strokes

Piston pumps:

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a fixed volume of fluid passes through two rotating, oval-shaped gears with synchronized close-fitting teeth for each revolution, thus shaft rotation can be counted to obtain specific flow rates

Oval gears

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these moveable disks are mounted on a concentric sphere located in a spherical chamber, and the pressure of the liquid passing through the chamber causes the disks to rotate in a circulating path without rotating about its own axis. Each disk rotation traps a known amount of fluid and the number of disk revolutions is counted, thus the flow rate can be calculated

Nutating disks

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these vanes are equally divided, rotating impellers inside a casing. The impellers are in continuous contact with the casing, and a fixed volume of liquid is swept through as the impellers rotate. The revolutions of the impeller are counted and flow rate can be determined.

Rotary vanes

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directly measure the flow rate of fluids, especially gases, and tend to be highly accurate—they are off less than 0.1 percent

Mass flow sensors

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Thermal mass flow sensor

The thermal mass flow sensor operates independently of density, pressure, and viscosity. This sensor uses a heated sensing element isolated from the fluid flow path where the flow stream conducts heat from the sensing element

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Coriolis mass flow sensor

The Coriolis flow sensor uses a vibrating U-shaped tube to measure fluid flow rate based on an inertial force phenomenon; flow path where the flow stream conducts heat from the sensing element.

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The visual flow sensor

called a variable area flow meter or a rotameter, consists of a vertically oriented glass or plastic tube with a larger end at the top and a metering float, which is free to move within the tube.

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Sensors that produce a resistance output proportional to the displacement or position. Linear potentiometers are essentially variable resistors, which are either wire-wound or conductive plastic and either rectangular or cylindrically shaped

Linear and rotary potentiometers

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a position sensor consisting of a trans- former with a movable core. The transformer has a primary winding and two identical secondary windings that are wound around a hollow tube containing the movable core, and the movable core is attached to the item whose position is to be measured.

The linear variable differential transformer (LVDT)

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Vision Systems Classifications

Binary systems

the lowest in cost and easiest to use, do basic visual inspections

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Vision Systems Classifications

Gray scale imaging

typically processes images using 256 levels of black and white

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Vision Systems Classifications

Color processing

uses information from the red, blue, and green color spectra to detect and differentiate shades of color relevant in food industry and pharmaceutical applications

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PC-based system

generally consists of a microcomputer with a processing board that includes dedicated vision ASICs

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Incandescent and quartz halogen

These commonly used light sources include devices ranging from standard household bulbs with reflectors to high-power quartz halogen lamps

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Fluorescent

The reduced infrared energy (heat) produced by this type of illumination, plus the extended life of the tube, make it more efficient than the incandescent and quartz halogen source

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LED

Arrays of LEDs are arranged in a variety of configurations, including circular and linear sources to light objects

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Xenon flash

When used as a strobe light source, the xenon flash tube is an important light source in vision applications.

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Lasers

The laser is an important source because it produces coherent light that does not disperse as it travels from the source to the target.