Quiz 2 Ch 15, 16, 17, 18

Most wiring for DDC is intended to carry _____.

0-10 Vdc

Most motors normally operate at _____.

125°F (52°C)

A controlled device that changes an input signal into mechanical motion.

Actuator

Which of the following is a type of temperature sensor used with a thermostatic motor control?

Bimetal device, Electronic sensor, & Sensing bulb

An automatic switch that opens a circuit if the current draw exceeds a predetermined level and must be manually reset.

Circuit breaker

The present condition as measured by sensors.

Control point

A device that operates based on signals from another device.

Controlled device

A circuit that responds to changes in signals from sensors and issues signals in response.

Controller

Opens a circuit when the current exceeds its limit and closes when it cools down.

Current-limiting fuse

If an HVACR system's average temperature was acceptable but its high was too high and low was too low, which one control should be adjusted to fix this?

Differential combination control

May only open a circuit if the current is too high and not if the motor is overheating.

External bimetal protection device

A device that blows immediately after its maximum rating is exceeded.

Fast-acting fuse

Information that is detected by a sensor in a conditioned area and sent to the controller.

Feedback

A piece of metal that melts to open the circuit when current rises too high.

Fuse

The opposition to the flow of alternating current.

Impedance

Used to shut down the compressor in the event of refrigerant loss.

Low-pressure safety control

Similar to a contactor, but it has built-in overload protection.

Motor starter

A device that is fast-acting but also has a time-delay feature.

Multipurpose fuse

A characteristic in which resistance decreases as the temperature increases.

Negative temperature coefficient (NTC)

Th e difference between the present condition and the desired condition.

Offset

Increases resistance to prevent current from conducting when temperature rises beyond a safe level.

PTC thermistor

A type of relay that uses a thermistor to protect motor circuits.

Positive temperature coefficient (PTC)

If an HVACR system was overall too warm and all values needed to be reduced at once in equal amount, which one control should be adjusted?

Range adjustment

The desired condition in an area

Set point

A type of relay that operates using only electronic devices.

Solid-state

What happens when a single-phase motor's start winding is left in the circuit when the motor reaches 60% to 75% of rated full-load speed?

The start winding may overheat.

A sensing device in an electronic temperature sensor.

Thermistor

A dual-element device that will not blow unless an overload condition exists for a certain period of time.

Time-delay fuse

A device that converts an input signal of one form of energy into an output signal of another form of energy.

Transducer

Used to detect changes in a thermistor's resistance.

Wheatstone bridge

For an oil pressure motor control to allow an HVACR system to continue operating, the oil pressure sensed must be _____.

above low-side pressure

The internal protection device in a three-phase motor will open _____.

all three phases

As the polarities of the stator's poles change due to the flow of _____, the polarity of the rotor also changes.

alternating current

A(n) _____ is a single-phase induction motor that has a start capacitor and a run capacitor wired in series with the start winding.

capacitor-start, capacitor-run (CSCR) motor

A(n) _____ is a single-phase induction motor that has a start capacitor wired in series with the start winding.

capacitor-start, induction-run (CSIR) motor

Split-phase motors are very popular in compressors in HVACR systems that use a(n) _____ as the metering device.

capillary tube

Potential relays operate based on _____.

cemf

The contacts of a(n) _____ change position when force applied to weights overcome spring pressure.

centrifugal switch

A high-pressure motor control is connected to the _____.

compressor outlet

The oppositely polarized voltage induced by the magnetic fi eld in the rotor is called _____ force.

counter electromotive

A _____ relay uses a weight or a spring to hold the start winding contact points open when the system is idle.

current

The condition value at which a device begins to operate is its _____.

cut-in

The condition value at which a device ceases to operate is its _____.

cut-out

If a commercial cooler's temperature is rising too high but should not be adjusted lower (to protect sensitive products), a technician should adjust the _____ control.

differential cut-in control

In order to produce a snap action, a bimetal strip is formed into a(n) _____.

disc

A(n) _____ has its stator windings arranged in pairs so that it can be used at two different voltages.

dual-voltage motor

Mechanical energy produced by the motor shaft divided by the power input to the motor is referred to as motor _____.

efficiency

When current from a power source fl ows through the field windings, it creates a(n) _____.

electromagnetic field

A closed-loop control system is closed because it does detect or use feedback from the conditioned space.

false

A major maintenance issue with ECMs is that their brushes wear out frequently and need replacing.

false

A start capacitor is used in a stator's run winding circuit.

false

ECMs usually start quietly but maintain an overwhelming roar during normal operation.

false

Most starting relays can be and often are rebuilt in an HVAC shop for later reuse.

false

Run windings are used for motor starting and additional torque.

false

The speed of dc motors is dependent primarily on the current's frequency and the number of poles in the motor.

false

Upon reaching rated full-load speed, a start capacitor is often added to a single-phase motor circuit.

false

VFDs are a great option to use when controlling the speed of dc motors.

false

A(n) _____ is an electromagnet whose polarity changes as the fl ow of current alternates in the field windings.

field pole

The wires wrapped around the fi eld poles of the stator are called _____.

field windings

The letter and number designation that indicates the physical dimensions of a motor is its _____ size.

frame

A VFD controls the speed of motors by changing the _____.

frequency of the electrical signal

The current level at which a motor's full-load torque and horsepower are reached is called the _____ amperage.

full-load

Current relays operate based on _____.

high inrush of current

Motors that start under load need _____.

higher starting torque

The amount of mechanical work that a motor can perform based on both motor speed and torque is the rated _____.

horsepower

A common mode of communication used in control systems is _____.

hydraulic, pneumatic, & electrical

Two prominent forms of inherent motor protection are _____.

impedance protected and thermally protected

Induction motors are ac motors that operate by using the magnetic fi eld generated in the stator to _____.

induce current in the rotor

The magnetic field created in the rotor has a polarity _____ of the polarity of the magnetic field in the stator windings.

induction

An electric motor operates based on the principles of electricity and _____.

magnetism

The start winding has a higher inductance than the run winding because it has _____.

more coil turns

ECMs have rotors made of _____ instead of coils of wire or metal bars.

permanent magnets

A(n) _____ is a single-phase induction motor that uses a single run capacitor in series with the start winding for the motor's entire operation.

permanent split capacitor (PSC) motor

The required voltage in the start winding necessary to energize a potential relay coil is called _____ voltage.

pickup

The stator's poles switch _____ with the applied alternating current.

polarity

Relays can be used to _____.

provide power directly to motors, add start windings to a motor circuit, & add start capacitors to a motor circuit

The number of units between when a device begins operation and ceases operation is its _____.

range

The set of numbers between and including cut-in and cut-out values is a device's _____.

range

Capacitors cause capacitive _____ in a circuit, which is the opposition to the flow of current that causes voltage to lag behind current in an ac cycle.

reactance

Th e attraction of unlike poles and _____ of like poles causes the rotor to rotate.

repulsion

A hermetic compressor's motor _____.

requires leakproof electrical connections & requires special cooling provisions

The interaction between the magnetic fields of the stator and rotor causes the rotor to _____.

rotate

The moving part inside an electric motor is the _____.

rotor

A(n) _____ is a low-torque, single-phase motor that has field poles that are split with part of each wrapped in a copper band to produce starting torque.

shaded-pole motor

Thee difference between synchronous speed and rated full-load speed is a motor's _____.

slip

The start winding has a higher resistance than the run winding because it is made of _____.

smaller gage wire

Current induced in the rotor creates an electromagnetic field that interacts with the electromagnetic field created by the _____.

stator

The stationary part inside an electric motor is the _____.

stator

Electrical connections are made in the _____ to control and power the motor.

terminal box

Pressure sensors use a(n) _____ to change their pressure signal into a mechanical signal.

thermistor

A sensing bulb is primarily used by _____ motor control.

thermostatic

A(n) _____ is an induction motor with three sets of stator windings operating on three separate power signals.

three-phase motor

NEC terms "continuous duty" and "intermittent duty" primarily deal with a motor's _____ rating.

time

Electric motors are rated at their operating speed under a full load.

true

Motor-driven fans used to circulate air around a condenser are often wired to run when the compressor runs.

true

One method of changing the speed of a belt-driven compressor is by replacing the pulley with one of a different size.

true

Signals sent by a controller may be used to change a system's operating parameters.

true

When a split-phase motor is starting, current is going through both the start and run windings.

true

A larger phase displacement leads to a higher starting torque, which means motors that use capacitors can start _____.

under heavier loads

A device used to reduce a compressor's load on start-up is called a(n) _____.

unloader