Final Exam Flashcards
Describe what sensors are and give several examples of sensors
- Devices that respond to physical stimulus and transmits a resulting impulse. (Ex: thermometer, motion sensor, pressure sensor)
Describe what actuators are and give several examples of actuators
- Mechanical response to stimulus, mechanism for moving or controlling something.
What is the difference between continuous and discrete sensors and actuators? Give examples.
Continuous devices can generate or respond to signals having an infinite number of levels or values (ex: 0-3.3 V), discrete devices can only respond to binary values (ex: high or low)
What is a pressure transducer?
Measures the pressure and then returns a scaled voltage.
What is the ratio of power and field related values in decibels?
P=10log(P/Po) for power
V=20log(V/Vo) for fields
What does monotonic mean?
Function is either increasing or decreasing.
input impedance.
Ratio of the rated voltage and the resulting current through the input port of the device with the output port open (no load)
output impedance.
Ratio of the rated output Voltage and short circuit current of the port (i.e. current when the output is shorted)
What is the difference between range and dynamic range?
Range is the lowest and highest values of the stimulus and dynamic range is the ratio between the upper and lower limits (absolute quantities) or span (relative quantities)
Error
Deviation from “ideal” aka uncertainty
Hysteresis
The deviation of the sensor’s output at any given point when approached from opposite directions
Saturation
A property of sensors or actuators when they no longer respond to the input changes
Deadband
lack of response or insensitivity of a device over a specific range of the input.
Excitation
electrical supply required for operation of an active sensor or actuator
Accuracy vs Precision
Accuracy - closeness of measured value to standard or known value.
Precision - closeness of 2 or more measurements to each other.
What are the 3 broad categories of electrical temperature sensors?
RTD, thermistor, and thermocouple
Thermocouples
uses 2 metal wires to produce a voltage relative to the temperature present in the junction between them.
Resistance Temperature Detectors (RTDs)
measures temperature based on the resistance changes in a metal resistor inside.
Thermistors
is like an RTD but contains a ceramic or polymer resistor instead of metal.
Self Heating in RTDs
subject to error due to rise in their temperature produced by the heat generated by the current used to measure their resistance.
What are the 3 broad types of transistors?
JFET, MOSFET and BJT
JFET
Junction Field Effect Transistor - voltage controlled, 3 terminal uni polar semiconductor device.
MOSFET
Metal Oxide Semiconductor Field Effect Transistor - voltage controlled field effect transistor that is electrically insulated from the main semiconductor channel. No current flows into the gate.
BJT
Bipolar Junction Transistor - Current regulating devices that control amount of current flowing through them from emitter to collector.
Name a transistor application
switching, digital logic, amplification
What is a Darlington Pair and why would you use it?
2 BJTs connected together. The Emitter of one is connected to the Base of the other to produce a more sensitive transistor with a larger current gain. Useful in applications where current amplification or switching is required
Load Regulation
indication of how much the load voltage will change when the load current changes
Line Regulation
indication of how much load voltage will change when the line (input, supply) voltage changes.
Shunt Regulator
a form of regulator where the regulating element shunts the current to ground. ex: Zener Diode
Series Regulator
provides an effective form of voltage regulation within a linear power supply. Improved efficiency and low noise.
Buck Regulator
DC to DC step down converter
Boost Regulator
DC to DC step up converter
Freewheeling (Flyback) Diode
used to eliminate sudden voltage spikes across an inductive load when supply current is suddenly reduced or interrupted.
What quantity is most likely associated with generation of electric fields and closely associated with generation of magnetic fields?
Current
Diamagnetic, Paramagnetic, Ferromagnetic
Diamagnetic (weak repulsion from strong fields)
Paramagnetic (weak attraction to strong fields)
Ferromagnetic (strong attraction, can form permanent magnets)
Inductive Proximity Sensors
as the sensor gets closer to the sensed surface the inductance of the coil increases if the sense surface is ferromagnetic.
Eddy Current Proximity Sensors
ability of AC magnetic fields to induce currents in conducting media. Currents produced in material create a field which opposes originals field reduces the net flux through sensor coil.
LVDTs
Linear Variable Differential Transformer, the distance between 2 coils of a transformer is varied.
Hall Effect Sensors
consists of a current carrying metal strip that is placed inside any transverse magnetic field. An EMF is developed across the edges of this current carrying metal strip. The magnitude of this developed EMF is depending upon the density of the flux and mobility of electron.
Brushed DC Motor
A brushed motor has a rotating set of wound wire coils which acts as an electromagnet with 2 poles. Poles push and pull against permanent magnets on outside of the motor. Inertia keeps motor going in proper direction.
Brushless DC Motor
uses a permanent magnet external rotor, 3 phases of driving coils, position sensor. Coils are activated by electronic speed controller as cued by signals from the rotor position sensors.
3 Parameters used to quantify motor behavior
Excitation Type, Voltage or current rating, Speed, Power, Efficiency
Servo Motors, Stepper Motors, and solenoids
Servo motors - continuous rotation motors
Stepper motors - incremental rotation
Solenoids - designed for short distance linear motion
Permanent Magnetic (PM) vs Variable Reluctance (VR) stepper motors
PM can only operate on DC Power
VR can operate on AC or DC
H-Bridge
configuration of relays, transistors or other devices to reverse the polarity of the energizing voltage.