Tpc 437 Control Systems Flashcards
(25 cards)
What is the main function of a control system?
Adjust a load to meet demand
Limit actuator movement
Maintain a variable at a setpoint
Measure an error accurately
Maintain a variable at a setpoint
What are the basic components of a control system?
Design conditions, controller, actuator
Sensor, controller, controlled device
Setpoint, controller, wiring
Thermostat, controller, transducer
Sensor, controller, controlled device
Air conditioning and refrigeration systems are commonly controlled by _____ control.
anticipatory
inverted
proportional
three-position
proportional
The power to operate a control system may come from
changes in the temperature
feedback
fluid under pressure
the refrigerant
fluid under pressure
An RTD responds to a change in temperature by undergoing a change in its
electrical resistance
external shape
internal pressure
temperature-resistance coefficient
electrical resistance
Relative humidity is defined as the amount of moisture in the air
divided by the amount it can hold
minus the temperature in °C
multiplied by the air flow rate plus the temperature in °F
divided by the amount it can hold
In a pressure sensor that uses a Bourdon tube, changes in pressure are sensed by changes in the _____ of the tube.
cross-sectional shape
diameter
length
position of sealed end
position of sealed end
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 ____
closed; closed
closed; open
open; closed
open; open
closed; open
Which of the following is an advantage of variable speed dies over older methods of controling the output of an ar-condoning or refrigeration system?
•Cost of electric service can be controlled
• Equipment can start up more smoothly
• Proportional control can be used
• System can run during “off hours”
Proportional control can be used
Unlike floating control, the proportional control is
continuous
discontinuous
instantaneous
slow
continuous
The air supply for a pneumatic control system requires which of the following?
Algorithm
Drier
Evaporator
Humidifier
Drier
A PE relay is used to control a device operated by _____
air pressure
electricity
positive electrostatic pressure temperature
electricity
Setting the gain of a controller determines how much a change in the____ affects the____
controlled variable; controlled device
deadband; controlled differential
error; controller output setpoint; proportional band
controlled variable; controlled device
Adding integral action to a controller improves system performance by reducing_____Adding derivative action improves performance by reducing____
changes in the error signal; offset
offset; overshoot and undershoot overshoot and undershoot; time delay time delay; changes in the error signal
offset; overshoot and undershoot
In pumpdown control, the compressor starts when the pressure____ in the___
decreases; condenser
decreases; suction line
increases; condenser
increases; suction line
increases; suction line
The high-pressure control in the discharge line of an air-conditioning or refrigeration system responds to high pressure by_____
closing the solenoid valve
opening the solenoid valve
shutting down the compressor
starting the compressor
shutting down the compressor
A differential-pressure oil-safety control shuts off the compressor if the difference in pressure between the____
and the oil pump ___ does not become high enough within a given time.
compressor crankcase; discharge
compressor crankcase; inlet
metering device; discharge metering device; inlet
compressor crankcase; discharge
In modulating the flow of water to hydronic terminals, the temperature control method has the advantage of
eliminating the need for a separate zone pump
having the three-way valve downstream from the coil
preventing system freeze-up in cold weather
using a simple on/off valve
preventing system freeze-up in cold weather
In setting up a preventive (PM) program, your first step should be to
create a log sheet for all PM functions
inspect the system in detail
shut the system down
test the system to find its operating limits
inspect the system in detail
To maintain oil pressure in a 10-hp reciprocating compressor, a ___ oil pump is used.
differential-speed
gravity-feed
positive-displacement
water cooled
positive-displacement
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.
• head pressure; maximum
• head pressure; minimum
• output temperature; maximum
• output temperature; minimum
head pressure; maximum
The main requirements for maintaining a pneumatic control system include
cleaning the controller often
removing and disassembling valves
repacking the actuator rods of damper motors
using high-pressure air to test for leaks
removing and disassembling valves
The main requirements for maintaining an electric or electronic control system include
checking electrical contacts for pitting
rebuilding electronic controllers removing and repairing solenoid actuators
repairing damaged switches
checking electrical contacts for pitting
Which of these control loops adjusts the setpoint automatically?
Closed loop
Open loop
Reset system
Self powered
Reset system
