[D2L] Midterm Flashcards by Billy Cho

What are 2 important things to remember with Solenoids? MULTI-SELECT

1) Never power the coil when it is off the stem
2) Coils are polarity sensitive
3) Solenoids must be installed in the correct direction with piping flow
4) Solenoids must be installed level

Never power the coil when it is off the stem
Solenoids must be installed in the correct direction with piping flow

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Why is the use of proper control terminology important?

1) Can result in unnecessary costs
2) Miscommunication or inaccurate uses of terms causes frustration
3) It can result in injury to equipment users
4) All of the above

All of the above

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What is an analog signal?

A control action that is continuously variable

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What is an example of digital signal?

A light switch

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What is a bimetal element?

two metals bonded together with different coefficients of thermal expansion

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An internally powered controller would most likely be used in which type of system?

HWT (Hot water tank)

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What is a closed loop system?

A control system that allows system feedback.

Open loop system does not allow system feedback

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What normal state should a high limit control be in?

normally closed

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What is a low limit control used for?

interrupt the system operation if the condition drops below the desired value

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What does it mean to modulate?

Any controlled movement that changes through tiny increments and decrements

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What is the Differential?

The difference in the values of a controllers on and off set points

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What is an example of an open loop?

a kitchen faucet

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What is a pressure controller?

Converts a pressure signal to electronic

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What is a flow (sail) switch used to control?

1) air
2) water
3) fluid flow
4) all of the above

All of the above

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What type of control system are relays and contactors considered?

electromechanical

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Relays are used when the electrical loads are rated 15 amps and over

False

Relays -> 15 amps and under
Contactors -> 15 amps and over

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On a call for cooling in a furnace, R to Y closes in the thermostat which also sends power to G

True

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Relays typically have both N.O. (normally open) and N.C. (normally closed) contacts

True

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What type is a timer?

1) electromechanical
2) electronic
3) thermostat
4) both A & B

both A & B

electromechanical
eletronic

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What device is used to protect end use devices only?

Overload device

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What is the most important factor with regards to piping design in low temperature applications?

compressor oil return

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When is an OFC (Oil Failure Control)used?

when a reciprocating compressor has a oil pump

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A crankcase heater helps reduce refrigerant migration and oil frothing on start up

True

How is compressor short cycling reduced?

Delay on break timer

What cycles in low temperature refrigeration? 1) defrost cycle 2) freezing cycle 3) warming cycle 4) both A & B

both A & B defrost cycle freezing cycle

What does DTC stand for?

defrost time clock

A timer motor in a time clock is powered at all times

True

If you want a pressure controller to turn on a compressor at 20psi and off at 2psi what should you set it to?

High event: 20psi Differential: 18psi

Refrigerant boiling out of the oil in a compressor crankcase can cause a system to short cycle

True

Why are electrical thermostats preferred over electromechanical? 1) more reliable 2) auto-changeover functions 3) more accurate 4) all of the above

All of the above

What must be done to a mercury thermostat to maintain set point accuracy?

Be level

What is a high limit control used for in a residential furnace?

shut off gas valve if heat exchanger becomes too hot

You have been asked to deal with a co-workers call back, the customer is complaining about his old furnace that was just fixed and now the blower is short cycling. What should you expect to find? 1) The differential is set too small on a fan/limit controller 2) The differential is set too great on a fan/limit controller

The differential is set too small on a fan/limit controller

What is a fan cut in cut out switch 120F-140F used for in a residential furnace?

Cuts in(activate) the fan at 140F Cuts out(deactivate) the fan at 120F

What is a manual reset on a high pressure switch?

If the unit trips on high pressure it will need to be physically reset

You just did a great job replacing a failed high pressure control. Before you leave the job what Saturated discharge temperature should you set the controller to?

135F

You are working on a job and finds a large contactor with a failed coil, what should you do?

Call the supplier and replace just the coil

What does an OFC protect?

Compressor running without oil

What is a heat exchanger an example of? 1) controller 2) controlled device 3) control agent 4) process plant

process plant

What is the actuator in a closed loop furnace system?

gas valve solenoid

If the thermostat is calling for cooling and you read 24v between R and Y which component is running?

Nothing, because they are not connected

If 0v is measured between R and Y what components should be running? 1) Indoor blower 2) Air conditioning 3) Heating 4) A & B

A & B

Furnace will be heating if 24v is measured across R and W

False, it should measure 0v to turn on the heat

What kind of control(s) do most RTU (roof top unit) use? 1) Electronic 2) Electromechanical 3) Both

Both Electronic & Electromechanical

What type of sensor can be formed in a Helix, disk or spiral shape?

bimetal strip

Where would you find an averaging element?

Across the face of a heating coil

Your boss asked you to pick up and replace a constant cut-in thermostat on a cooler at a Boston Pizza. Where will you mount the fast response element?

attached to the evaporator

What sensors react to pressure? 1) diaphragm 2) bellows 3) bourdon tube 4) all of the above

All of the above

Where is a bourdon tube most commonly used?

Refrigeration gauge

What does a transmitter do?

transmits signal to the actuator in the controlled device

What position should a heating zone valve be in the event of a power outage?

depends on the most recent signal from B.A.S.

You are in a mech room and see an oil failure control cover on the ground and reinstall it, Your apprentice asks why you bothered to, what do you say?

"It prevents the heat generated by the internal differential heater from escaping"

What is the purpose of a Refrigeration Fan Delay thermostat?

Prevent evaporator fans from spraying water after defrost

What do fuses protect?

loads

The motor on top of a zone valve is referred to as the

Actuator

You are doing a startup on a brand new WIC (walk-in cooler) and notice the compressor short cycling, which component do you probably suspect?

Solenoid