Chapter 4 Homework

The part of a limit switch that physically comes into contact with the target is called the ___________________.

actuator

Solenoid valves are available to control ________ flow

all of these

Fiber optic sensor systems

are immune to electrical interference

The type of pressure switch shown is

diaphragm

Which of the following would be classified as a pilot control device?

pressure switch

Selector switches require the operator device to be ________ instead of pushed or pulled to actuate the attached contact block

rotated

The ____ technique refers to the method used by photoelectric sensors to detect a target.

scan

The type of switch shown is a

spdt

Which of the following pressure switches contains a sealed chamber that has multiple ridges like the pleats of an accordion?

bellows

An inductive proximity sensor can be actuated by nonconductive materials.

false

An ultrasonic sensor requires a constant bias current between two of its terminals.

false

As the temperature of a thermistor with a negative temperature coefficient increases, its resistance increases.

false

Color detection and discrimination are not possible with photoelectric sensors.

false

In a through-beam scan sensor the emitter and receiver are housed in the same enclosure.

false

Limit switches contain no moving mechanical parts.

false

The NEMA and IEC symbols for a pilot light are the same.

false

The basic operating principle of thermocouples is that the electrical resistance of metals varies with temperature.

false

The contacts of an electromechanical relay are switched by energizing the contacts.

false

When the target enters the field of a capacitive proximity sensor the oscillator circuit stops oscillating.

false

A motor starter would normally be classified as a primary control device.

true

A pushbutton assembly can have multiple sets of contacts.

true

All open loop control systems operate without feedback.

true

All servo motors operate using a closed loop control system.

true

An AC solenoid rated for 120-V direct current if connected to a 120-V alternating current source would draw lower than normal current.

true

Capacitive proximity sensor applications can detect both metallic and non-metallic objects.

true

Compared to single break contacts, double break types enable the contact to handle higher voltages.

true

Drum switches are used for starting and reversing 1ф motors that are designed for reversing service.

true

Emergency stop pushbuttons must be of the maintained contact type.

true

Encoder sensors are used in applications such as robotic control where positions must be accurately determined.

true

For DC solenoids, a non-laminated frame and plunger is acceptable.

true

Generally, stepper motors are rated for less than 1 horsepower and are used in low-power position control applications.

true

Hysteresis is a desirable feature of a proximity sensor that may prevent it from chattering.

true

If an AC solenoid sticks in the open position a burnout of the coil is likely.

true

Inductive proximity sensors can detect metallic targets through non-metallic barriers.

true

Mushroom head pushbutton operators are used for emergency stop pushbuttons.

true

Never directly operate a motor with a proximity sensor.

true

One of the strengths of limit switches is that they can be used in most industrial environment due to their rugged design.

true

Pilot-duty devices are not normally used to switch horsepower loads.

true

Push-to-test pilot lights can be energized from two separate signals of the same voltage.

true

Sensors are devices that are used to detect and often to measure the presence of something.

true

Temperature switches open or close when a designated temperature is reached.

true

The detectable target for an inductive sensor is made of ferrous or nonferrous metals.

true

The normally open contact of a relay is closed any time the coil is energized.

true

The operating temperature range of the IC temperature sensor is much lower than that of a thermocouple.

true

The photoelectric sensor receiver is tuned to the emitter's modulation frequency and will only detect light pulses at the specific frequency.

true

The proximity switch leakage current is due to the switching characteristics of solid-state devices.

true

The usual approach taken to measure fluid flow is to convert the kinetic energy that the fluid has into some other measurable form.

true

Ultrasonic wind sensors are used on wind turbine systems to determine the wind speed and direction.

true

Which type of sensor is best for detecting liquid targets?

Capacitive proximity sensors

Which of the following sensors is designed to sense the strength of a magnetic field?

Hall effect sensor

Which of the following pushbutton operators would be used for an emergency stop pushbutton?

Mushroom-head pushbutton

The _______ pushbutton makes a circuit when it is pressed and returns to the open position when the button is released.

N.O

__________________ use light to detect the presence or absence of an object.

Photoelectric sensors

Which of the following scan sensors is best suited to detect shinny targets?

Polarized Retroreflective

The main difference between inductive and capacitive sensors is that capacitive sensors produce an ______________ field instead of an electromagnetic field.

electrostatic

A brushless DC motor, like the brush type, can be driven by connecting it to a source of direct current.

false

A magnetic pickup sensor generates a voltage that is proportional to the speed at which it is driven.

false

A microswitch is normally actuated by a permanent magnet.

false

A proximity sensor cannot detect the presence of an object without physical contact.

false

AC and DC contact current ratings are the same for a given switch.

false

All pressure switches use only N.O. (normally open) contacts.

false

All selector switches operate with spring return to provide momentary contact operation.

false

An N.C. (normally closed) pushbutton makes a circuit when it is pressed and returns to its open position when the button is released.

false

An encoder sensor is used to convert linear or rotary motion into an analog signal.

false

Limit switches are usually actuated by hand.

false

A float switch is used to sense the ____________ of a liquid.

height

The coil current for AC solenoids is primarily limited by the ______ of the coil.

inductive reactance

Which of the following would be classified as a mechanically operated switch?

limit switch

Which of the flowmeters operates by measuring the changes of induced voltage of a conductive fluid?

magnetic

A __________ solenoid valve blocks flow when the solenoid is de-energized and allows flow when the solenoid is energized.

normally closed

For a DC stepper motor the amount of rotation is directly proportional to the:

number of pulses

NEMA "types" enclosures are selected according to the

operating environment.

The _____ is the part of the pushbutton assembly that is pressed, pulled, or rotated by the person operating the circuit.

operator

The stepper motor converts electrical pulses into discrete rotor movements called ____________.

steps

Which of the following converts rotational speed into an analog voltage signal?

tachometer

Which of the following would not be classified as an actuator?

tachometer

Thermowells are tubular fittings used to protect

temperature sensors

Which of the following scan techniques is best suited for long-range scanning?

through-beam

The two basic parts of a photoelectric sensor are the ________________ and ________________.

transmitter, receiver

A dry contact refers to one that has both terminals available and neither contact is initially connected to a voltage source.

true

A microswitch can operate with extremely small pressure on its operating lever.

true

Using maintained contacts in emergency stop pushbuttons prevents a motor control process from restarting until the maintained pushbutton is physically reset.

true

An _____ sensor operates by sending high frequency sound waves toward a target and measuring the time it takes for the pulses to bounce back.

ultrasonic

When a metal object enters the high-frequency field of an inductive proximity sensor, it causes

a decrease of energy in the oscillator circuit.