Pnuematic Controllers Flashcards
(48 cards)
What are the two types of controllers
Pneumatic Controller 1:On-off Controller
Pneumatic Controller 2: Proportional Controller
Define a controller
A comparative device that receives, an input signal from a measurement device about a measured process variable and compares this value to a to a set point (predetermined control point value) and then determines the appropriate amount of input signal to send the FCE to provide corrective action within the loop
What is a pneumatic controller?
Mechanical device designed to measure temperature or pressure, then mechanically compare this info aka the input signal against the setpoint to determine the appropriate correctove air signal and transmits the corrective air signal to the final control element which is pneumatic control valve
What does the pneumatic controller operate through?
Coordination of it or pressure sentence system, and it’s air signal release system
What are the main components of an electrical transmitter
MEA
Mechanical Sensing device
Electrical transducer
Amplifier With feedback
Draw the electrical transmitter block diagram
….
Explain the electrical transmitter diagram
The input causes a change in the mechanical sense device, which generates a mechanical signal that is sent to the electrical transducer to be converted to an electrical signal.
Which is then applied to the amplifier, which increases the signal, aka output. There is also feedback between the amplifier and electrical transducer
Give examples of the mechanical sensing device in an electrical transmitter
Bourdon tube
Bellows
Diaphragm with linkages
What happens in the mechanical sensing device of the electrical transmitter
A force or potential is created when the process variable changes in value
What can the electrical transducer be
It can be a variable resistance, inductance or capacitance
When does the electrical property change?
In response to variations in the mechanical input
What is the purpose of the amplifier with feedback
To amplify the electrical change produced by the electrical transducer and to give feed back its output to electrical transducer to create an opposing force to the input
What is an On/Off control
Control that only recognizes that deviation exists and has only 2 extremes, i.e., 100% on or 100% off
What will the deviation between the setpoint and the measured pv cause in I/0 control
It will cause a full corrective signal to be produced
What are examples of an on off controller
A home hot water heater
Thermostat controlled air furnace
Compressed air to a furnace tank
Describe the operation of the On off controller
Using a home water heater. When the temperature of the water in the tank falls below the set point, the burner turns on until the water temp meets the setpoint, and then it turns off again It is only a matter of time before the water begins to cool again and the cycle repeats itself
What does the discrete controller hold the variable
It does not hold the variable at the set but keeps the variable within the proximity of the setpoint in the dead zone
What do the tuning parameters essentially determine the
The magnitude of the correction
The duration of the adjustment
The speed at which the adjustment is made
How much correction should be made, and what is it determined by?
The magnitude of the correction( the changed in the controller output) determined by the proportional mode
How long should the correction should be applied
The duration of the error determined by integral
How fast Should the correction be applied
The Speed at which the correction is made is determined by the derivative mode
What does proportional control react to when sending a corrective signal
The size of the deviation from the set point
How is the corrective signal adjusted the relation to the size of the error
The size of the corrective signal is adjusted to the size of the Error by changing the width of the proportional band
A narrow proportional band will cause
A large Corrective action in relation to the given amount of error
