Input pressure required to produce controller output values

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Discussion Overview

The discussion revolves around determining the input pressure required for a direct acting proportional pressure controller to achieve specific output values. It includes theoretical aspects of control systems, mathematical reasoning, and attempts to solve a homework problem related to the controller's gain and output signals.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • Some participants present the problem statement and equations related to the proportional pressure controller, including gain and proportional band calculations.
  • One participant calculates the proportional band (PB) as 33.33% and derives that this corresponds to 13.33 bar on the input scale.
  • Another participant provides a series of calculations for different output percentages, suggesting that 10% output corresponds to an input pressure of 18.3 bar and 90% output corresponds to 29 bar.
  • A later reply proposes a method for calculating the output based on the set point, gain, and offset, although it is presented as a guess and not confirmed.

Areas of Agreement / Disagreement

There is no clear consensus on the calculations or methods presented, as participants offer different approaches and interpretations of the problem. The discussion remains unresolved regarding the correct input pressures for the specified output values.

Contextual Notes

Participants express uncertainty about the next steps in their calculations and the application of the proposed methods. The discussion includes various assumptions about the controller's operation that are not fully clarified.

oxon88
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Homework Statement



A direct acting proportional pressure controller has a gain of 3, a range of 0-40 bar and is set to control at 25 bar. When the measured value and the desired value are equal, the output signal is 60%. Determine the input pressure required to produce controller output values of 10% and 90%

Homework Equations


Gain = 100 / % proportional band setting

The Attempt at a Solution

 
Last edited:
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Ho oxon,

So far I have read 1. How about providing 2 and 3 as well ? -- if only to avoid being shot into the black hole ...
 

Homework Statement



A direct acting proportional pressure controller has a gain of 3, a range of 0-40 bar and is set to control at 25 bar. When the measured value and the desired value are equal, the output signal is 60%. Determine the input pressure required to produce controller output values of 10% and 90%

Homework Equations


Gain = 100 / % proportional band setting
PB = 100/gain

The Attempt at a Solution



PB = 100/3 = 33.33%

33% of input scale (0-40 bar) = 13.33 bar

not sure where to go with this now...
 
ok here is what i got...

33.33% of input scale (0 - 40 bar) is 13.33 bar60% of 13.33 bar = 8 bar

50% of 13.33 bar = 6.67 bar

40% of 13.33 bar = 5.332 bar

30% of 13.33 bar = 4 bar0% Output = 25 - 8 = 17 bar

10% Output = 25 – 6.67 = 18.3 bar

90% Output = 25 + 4 = 29 bar

100% Output = 25 + 5.332 = 30.3 bar
 
Could it be that the recipe for your proportional controller is as follows (consult your notes or textbook - I'm just guessing)
  • set point is subtracted
  • result is converted to %
  • gain is applied
  • offset is applied
Example: 25 Bar in. 25 bar is subtracted. 0 Bar is 0% 0% is multiplied by 3 add offset 62.5% to get result
Example: 27 Bar in. You see what comes out. Now express the recipe in a formula.
 

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