Chapter 12 Flashcards
- measure a range of input condition and generate a range of output values
Analog Sensors
resistance temperature detectors and thermistors
Resistance as a function of temperature
thermocouples and solid state temperature sensors
Voltage as a function of temperature
a temperature-sensing device that detects a change in the resistance of a metal as a function of temperature
Resistance temperature detector (RTD)
are electronic components that exhibit a large change in resistance with a change in the device temperature.
Thermistors
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
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
integrated circuits (ICs) whose output is linearly proportional to a temperature scale, typically Celsius
Solid-state temperature sensors
devices that detect the force exerted by one object on another.
Pressure sensors
______________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
pressure is a function of the amount of deformation of an object.
Direct pressure sensors
Direct pressure sensors measure strain, which is
the amount of deformation of a body due to an applied pressure or force.
pressure is a function of the amount of deflection of an object
Deflection pressure sensors
pressure is a function of the difference in two measurements
Differential pressure sensors
pressure is a function of the deformation/deflection of a crystal or electronic component.
Piezoelectric and solid-state sensors
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.
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.
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.
those sensors that disturb the flow of the fluid that they are measuring.
Intrusive
those sensors that do not disturb the flow of the fluid that they are measuring
Non-intrusive
fluid flows rather smoothly parallel to the walls of the pipe.
Laminar flow
fluid flows down the pipe, but swirls within the flow
Turbulent flow
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
measurement methods of flow
the flow rate is determined based on the velocity of the fluid as it passes through a turbine.
Velocity
measurement methods of flow
the flow rate is determined by measuring all the fluid used.
Displacement
measurement methods of flow
the flow rate is determined based on the total volume of the fluid that passes through the sensor.
Mass
measurement methods of flow
the flow rate is determined by a visual reading of a graduated scale
Visual
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.
Orifice plate
Venturi
Pitot tube
Flow Nozzle
Elbow
Paddle wheel flow
Turbine flow
Vortex Flow
Electromagnetic Flow
Ultrasonic flow
Thermal mass flow
Coriolis flow
Visual flow
- 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
A __________is a flow-measuring device that consists of a gradual contraction followed by a gradual expansion within a fluid- carrying pipe.
venturi
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
A___________ is a narrowing spout installed inside a piping system to obtain a pressure differential.
flow nozzle
An existing__________ in the piping system can be used to obtain a differential pressure
elbow
This flow sensor is installed in a pipe so that the flowing fluid causes its paddlewheel to rotate.
Paddlewheel flow sensor
Turbine flow sensor
a fluid moves through a pipe and strikes the vanes of a turbine, the turbine will start to spin and rotate
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
Electromagnetic flow sensor
The electromagnetic flow sensor measures the electrical charges in flowing fluid, which are proportional to the fluid velocity
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.
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
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:
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
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
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
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
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
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.
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.
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
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)
Vision Systems Classifications
Binary systems
the lowest in cost and easiest to use, do basic visual inspections
Vision Systems Classifications
Gray scale imaging
typically processes images using 256 levels of black and white
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
PC-based system
generally consists of a microcomputer with a processing board that includes dedicated vision ASICs
Incandescent and quartz halogen
These commonly used light sources include devices ranging from standard household bulbs with reflectors to high-power quartz halogen lamps
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
LED
Arrays of LEDs are arranged in a variety of configurations, including circular and linear sources to light objects
Xenon flash
When used as a strobe light source, the xenon flash tube is an important light source in vision applications.
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.
