Hello, i am a new user of labview and i have trouble finding a way to calculate air presure in the tank

[Nick21C]

I need to calculate air presure in the tank and i know tank's volume, input presure [pin] and output valve opening percentage [n]. I have to make a LabView aplication which i can introduce [pin] and n and my aplication should be able to calculate presure in the tank.

[Vi.King]

Do you have a formula to calculate this?

If you do it should be easy enough to build in LabVIEW

[JimB.]

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@Nick21C wrote:

I have to make a LabView aplication which i can introduce [pin] and n and my aplication should be able to calculate presure in the tank.

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Then you should do that.

If you are stuck then you should provide some details of what you have tried and how you are stuck. You have not asked any questions, so you should not expect many answers.

[Bob_Schor]

Attach your efforts (be sure to attach the .vi files you create so that we can test your code).  Pictures of code can also be helpful for those that might not have the latest version of LabVIEW installed.  But please don't ask us to do your homework for you ... there is plenty of tutorial material available, both on the first page of this Forum and on the Web.

Bob Schor

[altenbach]

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@Nick21C wrote:

I need to calculate air presure in the tank and i know tank's volume, input presure [pin] and output valve opening percentage [n]. I have to make a LabView aplication which i can introduce [pin] and n and my aplication should be able to calculate presure in the tank.

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Is this a (1) simulation where [pin] and [n] are controls on the front panel or (2) a hardware application where these measurements obtained from external hardware?

LabVIEW does not really care where the inputs come from, so start with a simulation. You can implement the hardware connections later with a few trivial changes:

1. Place two controls on the front panel, one labeled "pin" and one labeled "n", unless you can come up with more descriptive terms. Decide on a useful datatype and control style (e.g. sliders)
2. I assume the "volume" is constant, so that can be a diagram constant for now.
3. Place a numeric indicator on the front panel and label it "pressure". decide on a useful style (e.g. gauge).
4. No you have three terminal on the diagram, two data sources and one data sink.
5. If you interactively want to use it and see the results as the inputs change, surround the terminals with a while loop.
6. Decide how fast the loop should spin and place an appropriate wait (e.g. 100ms is sufficient).
7. Now implement the math to calculate the output from the two control inputs and volume using the plain tools in the numeric palette and wire things up. What are the formulas? Is the math simple or do you need to tap into calibration curves? Is this an ideal gas? Is the input pressure constant or well regulated? How big is the valve compare to the volume?
8. Run the VI, change the controls and watch the result. Make sure the result is correct.
9. Easy! Right?

[Nick21C]

Thank You for indications, I will try.

[Nick21C]

hello, my formula is :

where: pin=1atm

            n=100%(full oppened), R=8.314,T=25C,V=2,M=29 

[altenbach]

So were you able to complete the assignment?

If you give a formula, you should give units for all parameters (e.g. P, F, M, t). Well, we can guess, of course.... 😉

So you have a differential equation. Did you solve it? What is the starting pressure of P? Is Pin the outside pressure? I guess after an infinite time, P=Pin. Are you sure n is percent (0..100%) and not fraction (0..1)?

Do you have a link where you got that formula?