Control Fundamentals ppt Flashcards
________ decides whether to make an adjustment
controller
An OPEN loop control loop has ___ feedback
NO
On open loop control loops, no feedback information is returned to the ________, changes must be made manually
controller
A CLOSED loop control loop has _______
feedback
On closed loop control loops, a ______ provides feedback to a controller which processes information and compares control point with set point
sensor
High voltage:
Low voltage:
Extra low voltage:
High voltage: 751+
Low voltage: 31v to 751v
Extra low voltage: 0 to 30v
Pneumatic controllers use ___ instead of ________, typically ___psig
air, electricity, 20psig
Variable refers to _____ temp
space
Medium refers to ___ you are trying to control
air
Overshoot and undershoot conditions are caused by ____ in the system
lag
Control agent is the mid in which the manipulated variable exists. In a steam heating system the control agent is the ______
steam
A device used to position dampers and control valves are
actuators
Series 90 electric actuators are being replaced by ____ _____ actuators
direct drive
Typical two position controls undershoot and overshoot to prevent system from short cycling causing damage to equipment. What is the downside?
lack of temperature control for comfort
Difference between the set point and and control point is known as? Also known as?
offset, deviation
The separation between heating and cooling is known as?
dead band
The series 90 low-voltage control circuit provides _________ control and can be applied to motorized valves and dampers
modulating
In modulating control, an actuator moves damper proportional to the sensed change in the controlled variable.
A 10 degree throttling range moves the actuator _____ of the total travel for each degree change in temp
1/10
Proportional control helps keep the room temperature _____ to set point
closer
Proportional ____ is the change in controlled variable required to change the controller output from gully open to fully closed
band
In _______ _______ control, reset of the control point is automatic
proportional integral
Proportional _______ control changes the final control element position to accommodate load changes while keeping the control point at or very near the set point
integral
- Proportional integral derivative control (PID) adds a derivative function that ______ any change and is ________ to the rate of change
- The more quickly the control point changes, the more corrective action the ____ system provides
- PID control, eliminates _____, faster
- opposes, proportional
- PID
- offset
What provides powers to the temperature sensor (RTD’s)
the controller
RtD exhibits large _______ changes, linear changes, or both over wide temperature ranges
resistance
A ________ is a solid state discrete sensor with a _______ temperature coefficient. As temp increases the resistance of the sensor decreases
thermistor, negative
Temp sensors:
- temperature sensors are created by welding together two ________ metals
- When this junction is heated, a ______ is generated
- amount of _______ is directly proportional to the ____
- dissimilar metals
- voltage
- voltage, temp
Thermocouples generate enough voltage to hold the _______ valve open
pilot
Only the ___ of the thermocouple should be heated
end
Thermopiles are different from thermocouples in that they generate a ______ voltage that is enough to run the actual gas valve
larger
As the temperature goes up on a thermocouple the _______ goes up
voltage
Humidity Sensors
- Humidity sensors use a __________ material that will expand or contract in response to changes in humidity
- Types of Humidity sensors; name 3
- hygroscopic
2. wood, hair, gold leaf, membrane
Define deadband
range between heating and cooling in which neither will turn on
describe proportional band?
change in controlled variable required to change controller output from fully open to fully closed
List different control loops and describe each one?
open - no feedback
closed- feedback
List three different mechanical control components?
actuator, valves, dampers
Name two different drive types of actuators?
electric, pneumatic
