Electrical Motor Control Midterm Review
NEMA-rated motors are designed to operate at plus or minus ____ percent of their rated voltage.
10
Magnetic control systems generally operate on ____________________ volts.
120
A metal bellows-type switch can sense pressures up to ____ psi.
2,000
Electrical ratings for the contacts of the basic micro switch are generally in the range of ____ volts AC.
250
____ proximity detectors will sense ferrous metals better than nonferrous.
All-metal
____________________ timers use a small AC synchronous motor to provide the time measurement for the timer.
Clock
____________________ pressure is the difference in pressure between the cut-in or turn-on pressure and the cut-out or turn-off pressure.
Differential
Connecting eleven-pin timers into a circuit is generally even simpler than connecting the coil to power.
False
Flow switches are used to detect the movement of air, but not liquid, through a duct or pipe.
False
If two of the lines supplying power to a three-phase motor are reversed, the motor will not reverse the direction of rotation.
False
In industrial applications, manually operated valves are generally used.
False
One advantage of the turbine-type sensor is that the turbine blade offers no resistance to the flow of the liquid.
False
Overloads are designed to protect the circuit from a short-circuit condition.
False
Pressure switches are the only pressure sensing devices that an electrician is likely to encounter on the job.
False
Push buttons are always shown as normally open.
False
Relays are electromechanical switches that lack auxiliary contacts.
False
Sensors targeting specific types of metal should be mounted as close to other metals as possible.
False
The Hall effect was discovered by Edwin H. Hall at Johns Hopkins University in 1979.
False
The Hall generator cannot be used in a manner similar to a limit switch.
False
The most complicated method of starting a motor is across-the-line starting.
False
The off-delay relay is often referred to as DOE, which stands for "Delay On Energize."
False
Three-phase motors must have an overload sensor (heaters or magnetic coils) in two of the three-phase lines.
False
Chapter 9
Float Switches
Chapter 10
Flow Switches and Sensors
Chapter 1
General Principles of Motor Control
Chapter 15
Hall Effect Sensors
Chapter 11
Limit Switches
____ are designed to produce an output voltage that is proportional to the strength of a magnetic field.
Linear transducers
Chapter 3
Manual Starters
The conductor size, fuse or circuit breaker size, and overload size are generally determined using the ____.
National Electrical Code
Chapter 4
Overload Relays
Chapter 12
Phase Failure Relays
____ timers operate by restricting the flow of air through an orifice to a rubber bellows or diaphragm.
Pneumatic
Chapter 8
Pressure Switches and Sensors
Chapter 16
Proximity Detectors
Chapter 5
Relays, Contractors, and Motor Starters
Chapter 13
Solenoid and Motor-Operated Valves
Chapter 2
Symbols and Schematic Diagrams
Chapter 14
Temperature-Sensing Devices
Chapter 6
The Control Transformer
Chapter 7
Timing Relays
A float switch is used when a pump motor must be started and stopped according to changes in the water (or other liquid) level in a tank or sump.
True
Integral horsepower manual starters with low voltage release automatically restart after a power failure and don't have to be manually reset.
True
Limit switches are drawn by adding a wedge to one of the four basic switches.
True
Limit switches are used to detect when an object is present or absent from a particular location.
True
Manual starters are characterized by the fact that the operator must go to the location of the starter to initiate any change of action.
True
Micro switches are used in small spaces that would never be accessible to a larger device.
True
Most industrial motors operate on voltages that range from 240 to 480 volts.
True
Motors are intended to operate on systems with balanced voltage.
True
Pressure switches are found throughout industry in applications where it is necessary to sense the pressure of pneumatic or hydraulic systems.
True
Proximity detectors are designed to detect the presence or absence of some object.
True
Standard temperature transmitters generally send a 4-20 ma signal to indicate the temperature range and are calibrated for a specific range.
True
The greatest difference between relays and contactors is the fact that contactors are equipped with large contacts that are intended to connect high-current loads to the power line.
True
The mercury bulb float switch does not depend on a float rod or chain to operate.
True
When a machine is installed, the motor, machine, and controls are all interrelated and must be considered as a unit.
True
When two dissimilar metals are joined at one end, on a thermocouple, and that junction is heated, a voltage is produced.
True
____ flow sensors operate on the principle that when a moving liquid strikes an object, a swirling current is created.
Vortex
The type of bumper arm used is determined by the ____ of the limit switch
application
The most common coil symbol used in schematic diagrams is the ____________________.
circle
The symbol for a float switch illustrates a ball float. It is drawn by adding a ____ to a line.
circle
All overload relays contain a set of normally ____________________ contacts.
closed
Regardless of the method used to sense pressure, all pressure switches activate a set of ____________________.
contacts
Anytime a motor has tripped on overload, the electrician should check the motor and circuit to determine why the overload tripped. The first step is generally to ____.
determine if the motor is actually overloaded
Diodes are used to suppress the voltage spikes produced by coils that operate on ____________________.
direct-current or DC
Many ultrasonic sensors have an analog output of voltage or current, the value of which is determined by the ____.
distance to the object
The continuous change of both amplitude and polarity of the magnetic field causes currents to be induced into the metal core material. These currents are called ____ currents.
eddy
It is a common practice to not ground one side of the control transformer. This is generally referred to as a ____ system.
floating
A(n) ____________________ valve is used to adjust the maximum air flow in a bubbler system.
hand
The ____ relay is so named because it uses a length of resistive wire connected in series with the motor to sense motor current.
hot-wire
Programmable controllers contain ____ electronic timers.
internal
Mechanically held contactors and relays are often referred to as ____ contactors or relays.
latching
When using a sensing pilot device to directly control the operation of a motor, you must make sure that the type of pilot device is equipped with contacts that can handle the rated current of the motor. These devices are generally referred to as "____________________" devices
line voltage
There are two major types of overload relays: thermal and ____.
magnetic
Some limit switches are momentary contact (spring returned) and others are ____________________ contact.
maintained
Motor control systems can be divided into three major types: ____________________, semiautomatic, and automatic.
manual
The ____ switch appears as a rubber bulb connected to a conductor.
mercury bulb
The ____________________ level gauge operates by emitting a high frequency signal of approximately 24 gigahertz into a tank and then measuring the frequency difference of the return signal that bounces off the product.
microwave
When a process has a definite on and off operation, or a sequence of successive operations, a(n) ____________________ timer is generally used.
motor driven
Schematics are always drawn to show components in their de-energized, or ____________________, state.
off
Fuses and circuit breakers are generally employed for circuit protection, and ____ are used to protect the motor.
overload relays
Generally, limit switches are used as ____________________ devices to control the coil of relays and motor starters in control circuits.
pilot
The number of ____________________ refers to the load contacts and does not include the number of control or auxiliary contacts.
poles
Solder melting-type overloads are often called solder ____________________ overloads.
pot
The ____________________ rating of control transformers generally ranges from 0.75 kilovolt-amperes, or 75 volt-amperes, to 1 kilovolt-ampere, or 1000 volt-ampere.
power
The liquid level in a bubbler system is sensed by ____ switches.
pressure
The term ____ means that the output voltage will be proportional to the supply voltage.
ratiometric
Air flow switches are often called ____________________ switches.
sail
Control transformers generally have ____ terminals connected to the primary and secondary leads.
screw
Vortex sensors insert a(n) ____________________ bar in the line to produce a vortex.
shedder
Push buttons that contain multiple contacts are often called ____ push buttons.
stacked
Two factors determine the polarity of the voltage produced by the Hall generator: the direction of current flow and the ____ of the ____ field.
strength, magnetic
Manual starters that are installed in a(n) ____________________ inside a wall are especially susceptible to ambient temperature problems.
switch box
Since thermocouples produce such low voltages, they are often connected in series. This connection is referred to as a(n) _____.
thermopile
In a MOV, the ____ switch is generally used to stop the motor when the valve is closed.
torque
To detect the amount of liquid or air flow, a ____ must be used.
transducer
Electronic overload relays employ a current ____ to sense the motor current.
transformer
Solid-state relays that are intended to connect alternating current loads to the line use a device called a(n) ____________________.
triac
Starters that are intended to protect motors that operate on 240 volts should contain ____ load contacts.
two
The percentage of heat rise in the motor caused by the voltage unbalance is equal to ____ times the percent squared.
two