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Pneumatic Circuit

Hi,

 

I am currently designing an MRI loading device driven by a pneumatic circuit. I use Labview to control a pneumatic regulator (giving a voltage output), a solenoid valve (as a switch) and load cells to measure the force I apply to my object. I am giving a constant voltage and I am measuring a certain load. My goal is to create a loop that when the load changes, the voltage readjusts to the original value in order to keep the load constant for the whole MRI scan. I have managed to control the regulator, the valve and the load cells separately but I am struggling to connect them in a loop. I would be open to any ideas that would allow me to connect these daqs together in a loop.

I have attached my vi.

 

Thank you very much.

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Message 1 of 6
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You haven't provided much detail, but off the top of my head, I'd say you are looking for some kind of simple PID control?

 

The PID Controller & Theory Explained - NI

LabVIEW Pro Dev & Measurement Studio Pro (VS Pro) 2019 - Unfortunately now moving back to C#, .NET, Python due to forced change to subscription model by NI. 8^{
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So basically, I have used information from NI website and different forums to control the voltage-pressure of the regulator, the status of the solenoid valve (on/off) and reading the data from the load cells individually, using the NI USB6008 for the regulator and the solenoid and a different NI DAQ for the load cells. What I want to do is, firstly apply a certain voltage-pressure to the regulator. This will trigger the solenoid valve to the on status and move forward and apply a force to the load cells through a loading device that I have built. Then I want to implement an if/else condition. If the load changes between a certain range, then I want to give a signal to the regulator to increase or decrease the voltage and hence the pressure. This will control the status of the solenoid and hence the load will re-adjust in the original value. Is is this more understandable and if so, do you think that a PID controller is still the solution to this problem?

 

Thank you very much.

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Message 3 of 6
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You promised, but forgot to attach, your VIs (don't apologize -- I do this all the time, absent-mindedly).  If you are using LabVIEW 2022 or 2023, please "Save for Previous" and specify LabVIEW 2019 or 2021.

 

Bob Schor

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Message 4 of 6
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Actually, if I understand your system. You have;

1) A Voltage regulated pneumatic source where pressure is scaled somehow to voltage applied
2) A Solenoid that applies the source to the load
And hopefully 3) some means of dumping the compressed air from the load.

What is the Load Cell telling you that a slide rule can't? You know your system size in square inches and the pneumatic pressure in pounds per square inch. If you don't know the system size you can calculate it really easy by calibrating the regulator with the load cell.

"Should be" isn't "Is" -Jay
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I attached the code.

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