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Instrumentation > Pnuematic Controllers > Flashcards

Pnuematic Controllers Flashcards

1
Q

What are the two types of controllers

A

Pneumatic Controller 1:On-off Controller
Pneumatic Controller 2: Proportional Controller

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2
Q

Define a controller

A

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

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3
Q

What is a pneumatic controller?

A

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

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4
Q

What does the pneumatic controller operate through?

A

Coordination of it or pressure sentence system, and it’s air signal release system

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5
Q

What are the main components of an electrical transmitter

A

MEA
Mechanical Sensing device

Electrical transducer

Amplifier With feedback

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6
Q

Draw the electrical transmitter block diagram

A

….

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7
Q

Explain the electrical transmitter diagram

A

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

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8
Q

Give examples of the mechanical sensing device in an electrical transmitter

A

Bourdon tube
Bellows
Diaphragm with linkages

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9
Q

What happens in the mechanical sensing device of the electrical transmitter

A

A force or potential is created when the process variable changes in value

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10
Q

What can the electrical transducer be

A

It can be a variable resistance, inductance or capacitance

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11
Q

When does the electrical property change?

A

In response to variations in the mechanical input

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12
Q

What is the purpose of the amplifier with feedback

A

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

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13
Q

What is an On/Off control

A

Control that only recognizes that deviation exists and has only 2 extremes, i.e., 100% on or 100% off

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14
Q

What will the deviation between the setpoint and the measured pv cause in I/0 control

A

It will cause a full corrective signal to be produced

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15
Q

What are examples of an on off controller

A

A home hot water heater
Thermostat controlled air furnace
Compressed air to a furnace tank

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16
Q

Describe the operation of the On off controller

A

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

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17
Q

What does the discrete controller hold the variable

A

It does not hold the variable at the set but keeps the variable within the proximity of the setpoint in the dead zone

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18
Q

What do the tuning parameters essentially determine the

A

The magnitude of the correction
The duration of the adjustment
The speed at which the adjustment is made

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19
Q

How much correction should be made, and what is it determined by?

A

The magnitude of the correction( the changed in the controller output) determined by the proportional mode

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20
Q

How long should the correction should be applied

A

The duration of the error determined by integral

21
Q

How fast Should the correction be applied

A

The Speed at which the correction is made is determined by the derivative mode

22
Q

What does proportional control react to when sending a corrective signal

A

The size of the deviation from the set point

23
Q

How is the corrective signal adjusted the relation to the size of the error

A

The size of the corrective signal is adjusted to the size of the Error by changing the width of the proportional band

24
Q

A narrow proportional band will cause

A

A large Corrective action in relation to the given amount of error

25
Q

A wider proportional band will cause

A

A smaller corrective action in relation to the same amount of error

26
Q

What is the proportional band express in terms of? Give its formula

A

The percentage change in error that will cause 100% change in the controller output
PB= (Δ input% divided by Δ output % ) x 100=100/gain

27
Q

What is proportional gain expressed as?

A

The percentage change in output divided by the percentage change in input

28
Q

What is the gain formula?

A

Gain = Δ input% /Δ output %
Gain = 100/PB

29
Q

What is proportional control?

A

This type of action is where the controller produces an output signal, which is proportional to the error

30
Q

What is the proportional control action represented by?

A

K e
Where k is a constant and E is the error

31
Q

When is integral mode added?

A

If offset cannot be tolerated in the proportional only control

32
Q

What does PI stand for?

A

Proportional plus integral control

33
Q

What does the integral action integrate and what does it cause?

A

It integrates any difference between the measurements and it’s set point and causes the controller to change until the difference between the measurement and set point is zero

34
Q

What is the integral action represented by?

A

K/R ∫ edt

35
Q

What is the purpose of the integral mode and how does it achieve this?

A

To return the process variable to the set point and it does despite repeating the action of proportional mode as long as the error exist

36
Q

What is the advantage and disadvantage of integral mood?

A

The advantages it eliminates errors
Reset wind up and possible overshoot

37
Q

What is another name for integral action?

A

Reset action

38
Q

What is another name for proportional action?

A

Offset action

39
Q

How is the PID controller accomplished

A

I added derivative adjustment to the PI controller

40
Q

What does the derivative action give?

A

An output which is proportionate to the derivative or rate of change of error

41
Q

What is another name for the derivative action?

A

Rate control

42
Q

What’s mathematical expression is the derivative action represented by?

A

KD de/dt

43
Q

What kind of function is the rate action

A

Rate of change of the error

44
Q

What action is the of rate action?

A

This action is to apply immediate response that is equal to the proportional plus reset action that would have occur number of minutes in the future

45
Q

What is the rate action unit?

A

Minutes

46
Q

What is the advantage and disadvantage of the derivative action?

A

Rapid outputs reduces the time that is required to return the PV to the SV in a slow process
Dramatically amplifies, noisy signals

47
Q

What is a major limitation of the flopper amplifier

A

It has a limited a handling capacity

48
Q

What is another name for the pneumatic amplifier?

A

Air relay

Instrumentation (10 decks)

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