Tpc 437 Flashcards
What is the main function of a control system?
Maintain a variable at a set point
What are the basic components of a control system?
Sensor, controller, controlled device
Air conditioning and refrigeration systems are commonly controlled by?
Proportional control
Which of these control loops adjust the set point automatically?
Reset system
The power to operate a control system may come from?
Fluid under pressure
An RTD responds to a change in temperature by undergoing a change in its?
Electrical resistance
Relative humidity is defined as the amount of moisture in the air…
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?
Position of the sealed end of the tube
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
Open
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?
Proportional control can be used
Unlike floating control, the proportional control is?
Continuous
The air supply for a pneumatic control system requires which of the following?
Drier
A PE relay is used to control a device operated by?
Electricity
Setting the gain of a controller determines how much a change in the __________ affects the __________.
Controlled variable
Controlled device
Adding integral action to a controller improves system performance by reducing __________ . Adding derivative action improves performance by reducing ___________.
Offset
Overshoot and undershot
In pumpdown control, the compressor starts when the pressure __________ in the _______.
Increases
Suction line
The high-pressure control in the discharge line of an air conditioning or refrigeration system responds to high pressure by?
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
What kind of capacity control is commonly used on large reciprocating compressors?
Cylinder unloading
In modulating the flow of water to hydronic terminals, the temperature method has the advantage of?
Preventing system freeze up in cold weather
In setting up a preventative program, your first step should be to?
Inspect the system in details
To maintain oil pressure in a 10-hp reciprocating compressor a ____________ oil pump is used
Positive displacement
To adjust the water regulating valve on a water cooled condenser, you should turn the adjusting screw until the ________ is at the designated valve. You should make this adjustment when the equipment is running at _________ load.
Head pressure
Maximum
The main requirements for maintaining a pneumatic control system include?
Removing and disassembling valves
The main requirements for maintaining an electric or electronic control system include?
Checking electrical contacts for pitting
