437

Question 1

what is the main function of a control system

Answer 1

maintain a variable set point

Question 2

what are the basic components of a control system

Answer 2

sensor controller; controlled device

Question 3

air conditioning and refrigeration systems are commonly controlled by ___ control

Answer 3

proportional

Question 4

which of these control loops adjusts the setpoint automatically

Answer 4

reset system

Question 5

the power to operate a control system may come from

Answer 5

fluid under pressure

Question 6

an RTD responds to a change in temperature by undergoing a change in its

Answer 6

electrical resistance

Question 7

relative humidity is defined as the amount of moisture in the air

Answer 7

divided by the amount it can hold

Question 8

in a pressure sensor that uses a bourdon tube changes in pressure are sensed by changes in the ___ of the tube

Answer 8

position of sealed end

Question 9

an air conditioning system has a two position damper in the duct bringing outside air into the building and a second two position damper in the return air duct. when the system shuts down the outside air damper should be ___ and the return air damper should be ___

Answer 9

closed; open

Question 10

which of the following is an advantage of variable speed drives over older methods of controlling the output of an air conditioning or refrigeration system

Answer 10

proportional control can be used

Question 11

unlike floating control the proportional control is

Answer 11

continuous

Question 12

the air supply for a pneumatic control system requires which of the following

Answer 12

drier

Question 13

a PE relay is used to control a device operated by

Answer 13

electricity

Question 14

setting the gain of a controller determines how much a change in the ___ affects the ____

Answer 14

controlled variable; controlled device

Question 15

adding integral action to a controller improves system performance by reducing ____ adding derivative action improves performance by reducing ______

Answer 15

offset; overshoot and undershoot

Question 16

in pumpdown control the compressor starts when the pressure ___ in the ____

Answer 16

increases; suction line

Question 17

the high pressure control in the discharge line of an air conditioning or refrigeration system responds to high pressure by

Answer 17

shutting down the compressor

Question 18

a differential pressure oil safety control shuts off the compressor if the difference on pressure between the ____ and the oil pump ___ does not become high enough within a given time

Answer 18

compressor crankcase; discharge

Question 19

what kind of capacity control is commonly used on large reciprocation compressors

Answer 19

cylinder unloading

Question 20

in modulating the flow of water to hydronic terminals the temperature control method has the advantage of

Answer 20

preventing system freeze up in cold weather

Question 21

in setting up a preventive program your first step should be to

Answer 21

inspect the system in detail

Question 22

to maintain oil pressure in a 10_hp reciprocating compressor a ____ oil pump is used

Answer 22

positive displacement

Question 23

to adjust the water regulating valve on a water cooled condenser you should turn the adjusting screw until the ____ is at the design value. you should make this adjustment when the equipment is running at ___ load

Answer 23

head pressure; maximum

Question 24

the main requirements for maintaining a pneumatic control system include

Answer 24

removing and disassembling valves

Question 25

the main requirements for maintaining an electric or electronic control system include

Answer 25

checking electrical contacts for pitting