ELEC 225 Ind Elec & Controls

The off-delay relay is often referred to as DOE, which stands for "Delay On Energize."

False

Limit switches are used to detect when an object is present or absent from a particular location.

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

When a relay is energized, all the contacts controlled by that relay change position.

True

The most complicated method of starting a motor is across-the-line starting.

False

What is the speed of a 4 pole motor running at 45 Hz with 10% slip?

1215

A metal bellows-type switch can sense pressures up to ____ psi.

2,000

What is the speed of a 4 pole motor running at 200 Hz with 5% slip?

5700

____ proximity detectors will sense ferrous metals better than nonferrous.

All-metal

____ voltage controls are simply controls that do not employ the use of a control transformer to change the voltage to a lower value.

Line

What letter indicates the secondary connection on a transformer?

X

The type of bumper arm used is determined by the ____ of the limit switch

application

iring diagrams are sometimes used to install new control circuits, ____ used for troubleshooting existing circuits.

but they are seldom

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

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

MOV-Motor Operating Valves employ an __________ to open or close the valve.

electric motor

Solenoid valves contain two distinct parts, the ____ part and the valve part.

electrical coil

It is a common practice to not ground one side of the control transformer. This is generally referred to as a ____ system.

floating

When using the NTC thermistor, resistance goes up when temperature ________

goes down

Programmable controllers contain ____ electronic timers.

internal

Mechanically held contactors and relays are often referred to as ____ contactors or relays.

latching

After numbering components, connection of the circuit is made by connecting ____ numbers.

like

There are two major types of overload relays: thermal and ____.

magnetic

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

Schematics are used ____ to connect or troubleshoot a control circuit.

more than any other type of diagram

Photo-operated devices fall into one of three categories: photovoltaic, photoemissive, and ____.

photoconductive

The liquid level in a bubbler system is sensed by ____ switches.

pressure

Control transformers generally have ____ terminals connected to the primary and secondary leads.

screw

Industrial motor wiring diagrams will typically____ motor connections.

show the

Push buttons that contain multiple contacts are often called ____ push buttons.

stacked

Two-wire control circuits control the operation of three-phase motors by controlling the power applied to the motor ____.

starter coil

The notation (2300V 3q 60 Hz) means that the motor is ____-phase.

three

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

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

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

Most control schematics are numbered to aid the electrician in troubleshooting.

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

When two dissimilar metals are joined at one end, on a thermocouple, and that junction is heated, a voltage is produced.

True

Power factor is

True Power/Apparent Power

NEMA-rated motors are designed to operate at plus or minus ____ percent of their rated voltage.

10

Electrical ratings for the contacts of the basic micro switch are generally in the range of ____ volts AC.

250

What is the speed of a 3 phase, 460 vac motor, 2 pole, with 5% slip?

3420

If two of the lines supplying power to a three-phase motor are reversed, the motor will not reverse the direction of rotation.

False

Overloads are designed to protect the circuit from a short-circuit condition.

False

The method used for developing wiring diagrams is the same as the method used for installing new equipment.

False

Three-phase motors must have an overload sensor (heaters or magnetic coils) in two of the three-phase lines.

False

When the cad cell is in the presence of light, its resistance is high.

False

____ timers operate by restricting the flow of air through an orifice to a rubber bellows or diaphragm.

Pneumatic

The _______ temperature sensor is more accurate than the _______ sensor.

RTD, Thermistor

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

NEC Section 430.72(C) lists requirements for the protection of transformers employed in motor control circuits.

True

Photodetectors can be used to sense the presence or absence of almost any object.

True

Schematic and wiring diagrams are the written language of control circuits.

True

Schematics in industry are often complicated and may contain several pages.

True

Single phasing causes the two phases that remain energized in a three-phase motor to increase current by and average of 173%.

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

____ flow sensors operate on the principle that when a moving liquid strikes an object, a swirling current is created.

Vortex

In the float switch circuit, what happens when motor starter M1 de-energizes?

The pump motor stops.

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

Because the current surge in starting multiple motors is too great for the system, there must be a delay between the starting of each motor.

True

Sensors targeting specific types of metal should be mounted as close to other metals as possible.

False

Most pilot devices, such as float switches, pressure switches, and limit switches, usually contain more than two contacts.

False

One advantage of the turbine-type sensor is that the turbine blade offers no resistance to the flow of the liquid.

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

The term ____ means that the output voltage will be proportional to the supply voltage.

ratiometric

Connecting eleven-pin timers into a circuit is generally even simpler than connecting the coil to power.

False

Control circuits can be divided into two major types: three-wire control circuits and four-wire control circuits.

False

Flow switches are used to detect the movement of air, but not liquid, through a duct or pipe.

False

When a machine is installed, the motor, machine, and controls are all interrelated and must be considered as a unit.

True

The conductor size, fuse or circuit breaker size, and overload size are generally determined using the ____.

National Electrical Code

In the on delay timed starting circuit, 10 seconds after coil TR2 energizes, contact ____ closes.

TR2

The orifice plate flow sensor creates a differential pressure, which is sent to a transducer, and then converts the signal to an output signal, such as a 4-20 ma signal, which the PLC control system can read.

True

Notation is generally used to help the industrial electrician interpret the meaning of certain components and find contacts that are controlled by coils.

True