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pressure controller design help

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hemnath

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Hi,
I would like to design a digital pressure controller. First of all, I would like to generate the pressure using pump and control the pressure output using PID algorithm by comparing the set point and measured output value. Is it right?

Please suggest any pressure pump.

Range can be of 10 bar.

Please share your thoughts.
 

Easyrider83

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PID is suitable for inertial systems for proportional control. For your purpose pressure relay will be enought.
 

hemnath

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Is it possible to control the output pressure using pressure relay?

What is that term. Can you provide some products with the link.

- - - Updated - - -

First problem is, i want to generate the pressure. Please suggest some sources or some products link.
 

BradtheRad

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Electric inflator for vehicle tires. Works on 12V. Available in auto parts stores.

Air pump for blood pressure readers. Works on a few volts. Probably can't be purchased by itself. Might need to extract pump from a machine.

Air pump for aquarium. Very low pressure. Runs on AC house voltage.
 

Warpspeed

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Usual way is to run an air compressor into a storage tank at higher pressure, say 12 Bar.
The compressor would have on/off control, set with a standard air pressure switch.
The pressure in the tank might vary between 11 to 12 Bar, for example.

Then use a pressure regulator on the output set to provide a constant 10 Bar regulated line pressure.

Portable Air Compressor 145 PSI.jpg
 
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FvM

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As said, technical compressed air systems are using compressor on-off control together with pressure tanks and mechanical pressure regulators.

Nevertheless analog pressure control using a variable speed compressor is an option for special purposes. What's your application?
 

Warpspeed

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That "Pascal 100" is only a only a pressure simulator, it does not actually generate any real pressure.

What it does do is generate extremely precise values of voltage or resistance to take the place of a pressure sensor, or temperature sensor.

If you want to generate actual real test pressures, you need what is called a dead weight pressure tester. These are a very simple mechanical device where a known weight is set upon top of a vertical piston of very precise known area.

This is a purely laboratory grade calibrated mechanical instrument, there are no electronics involved.

deadweighttester.jpeg
 

FvM

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That "Pascal 100" is only a only a pressure simulator, it does not actually generate any real pressure.
Presume you didn't read the datasheet thoroughly.

The Pascal 100 has an integrated pressure/vacuum generation by means of a built in hand pump from-0.9 ... +21 bar (-13 ... +300 psi). The presence of a fine precision regulator allows the operator to adjust small pressure increments.

Anyway, this calibrator hand pump is an expensive precision instrument which can't be easily mimicked by off-the-shelf components or some DIY design. The same with the instrument shown in your post.
 

Warpspeed

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The instrument shown in my post is fairly typical of a traceable laboratory pressure standard.

The one I once used came in a polished wooden wooden box with a whole range of pistons and circular weights for both imperial and metric calibration.
The clever thing about this is you spin the circular weights, and the well oiled piston also spins in its bore, to completely eliminate static friction.

A 10 pound weight on top of a one inch area piston obviously creates 10 psi test pressure.
There are really tiny needle like pistons that can generate thousands of Psi test pressures exactly the same way.

Dead simple, extremely accurate, and pretty foolproof.

There are several types of optional pumps for various pressures, but only to displace enough fluid in any interconnecting line just enough to raise the piston far enough to spin freely.

These dead weight testers are still the ONLY recognised instruments for serious traceable laboratory pressure calibration.
You would have a great deal of trouble convincing people to use some electronic box to replace this accepted time proven method.
 

c_mitra

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Common pressure sensors are basically force sensitive resistors: something similar to conducting rubber mats. The higher the force, the greater the conductance.

Commercial pressure sensors (actually they measure force; the force is applied on a fixed area) use patented materials but the idea remains the same.
 

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Thanks for your information guys.

I would like to collect some more information before getting my hands dirty. Assume I have generated 20 bar of input pressure. my set point valve is 10 bar output.

My understanding,
Lets say I have a controller with pressure sensor with a accuracy of 0.01%. The output port which is connected to the load is also connected to pressure sensor to sense the output pressure. When the pressure value is not equal to set point value, the valve which is connected to the output port is controlled by the controller which uses PID algorithm. Am I right?
 

FvM

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Making an electronic pressure regulator requires a suitable proportional valve. I guess you don't have any and neither know where to get it?
 

paulfjujo

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hello,


These are a very simple mechanical device where a known weight is set upon top of a vertical piston of very precise known area.

in the past, we used the "Balance de Boudon" to calbrate pressure sensor up to 300 bars..
it was a oil system , calibrated weights , and turn a littel pump manualy to get an equilibre.. Very precise tools , but very heavy , not portable..
Now we have emnbedded portable system for low air pressure <=10 bar , wich can provide the air pressur ..but very low flow..

You have to take care about the air flow .. wich can have a big influence about accuracy.
 

hemnath

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@FvM: Guess you found what i require. But the thing is, it is very expensive. I thought of designing my own using solenoid valves.
 

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