Input pressure required to produce controller output values

[oxon88]

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

 

[BvU]

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 ...

 

[oxon88]

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...

 

[oxon88]

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

 

[BvU]

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.