ufo900

i solved it in another way..

another question:

i need to make a sort of pid NOT realtime.. i explain this:

if I put a sine wave with frequency 1Hz i need the system to try to follow the wave..

sometimes it does not (the system is late with high frequency) but i need that the system follows the sine wave anyway..

how can i do that?

Example:

sine wave(0s)=0

temperature wave(os)=0 (OK)

sine wave (1s)=1

temperature wave(1s)=0,95 (acceptable)

sine wave(2s)=2

temperature wave(2s)=1,7 (not acceptable)

every value after 2sec is late. So when sine wave reaches the maximun value (example 5 for 5sec) the temperature wave is lower that 5 (example 4.5).

The sine wave is now going down but the temperature wave still going up: the temperature doesn't reach the value 5 because when it is 4.85 the sine wave is going down and so the temperature has to follow the sine wave.

At the end i have the sine wave as a sine wave (obvious) but the temperature wave as a triangle wave.

How can i force the temperature to follow the sine wave, without thinking about its late?

Thank you

little up

Sorry, we got into another discussion there :-)

So back to your original question.

"how to visualize the frequency as X and amplitude as Y? "

When using a FFT power spectrum, the X axis is in frequency.

It starts at Frequency 0 Hz and every x value has a delta f increment.

thank you about that but now I have another "PID problem".

I have some issues to apply PID into my system..

I can do a PID control by simulating a system only in temperature but issues if I want a voltage control that depends of temperature value.

Attached here PID subVIs I use and the program with the other subVI.

Hope you can help me apply PID into it.

Thank you

VIs(1).zip

that''s right, but anyone could help me solving the problem? Thank you all

Ok, let me try to see if I'm understanding.

You have a signal (a temperature in this case) that is oscillating in some fashion - possibly not sinusoidally - and you want to track the frequency of this oscillation over a period of time (which one assumes must be longer than the period of the osciallation) to look, for example, for a drift in the frequency of the oscillation.

Assuming this is correct, what you need to do is to take a sample of your data that is longer than the expected oscillation period but shorter than the time over which you expect the frequency to change. Take an FFT Power spectrum of this sample. This gives you the signal as Y(f) vs f where f is the frequency (which you would normally plot on the X axis). You want the value of f for which Y(f) is maximum as that will represent the fundamental frequency of the oscillation. You then repeat this process at different times, generating a plot of f vs t.

well the oscillation of the signal is "casual" if it is not touched (it depends on the real temperature of the ambient) but i need to control voltage of a heater to make the oscillation of the temperature zero (costant value), one frequency (sine oscillation) or in a way that the user is defining (square or something).

the problem is actually this: how to write the code, starting from the temperature array ending to the graph..

Sounds like you need to use an XY Graph or XY Chart.

well i did but nothing changed.

maybe i can explain better:

I need to graph the spectrum of the temperature wave (input of a NI 4351 connected to a termocouple) (Vi attached named temperatura.vi)

I did the FFT amplitude and phase spectrum and it visualizes the spectrum in X=0 and Y=frequency (i guess)

But i need to graph the frequency of the signal as in the example in the attached VI (vicreate.vi).

How to do that, using the incoming instrumental signal?

Someone told me to use filter anti.aliasing and other stuff but how to implement in the attached code?

Thank you

temperatura.vi

Years ago I implemented the algorithm from this link. It’s not that hard to write in LabVIEW. It’s my oldest bit of code still in use (and I would be embarrassed to post it), but I’ve found it very reliable.

— James

well thank you but i already implemented the pid control.

I have another issue now as you can see above here

If you can make up a VI that simulates the HW-signals, it's easier to help you out and for me to understand what you are looking for.

here you go

vicreate.vi

frequency is visualized as Y and time as X

how to visualize the frequency as X and amplitude as Y?

I don't understand what you mean.

Do you just need to plot the temperature?

In my PID graphs, I normally plot the Control signal (maybe voltage 0-10v) and also the temperature.

I use different Y scales for the two plots.

ok I understand that, but i need to plot the spectrum of the signal, the frequencies of the signal.. don't know how to explain in a different way

Another minor issue.

I need to graph the spectrum of the temperature wave..

I did the amplitude and phase spectrum but anything changed: no graph visualized..

How to do that?

I saw that trick but (example) in PID.vi i have a function that recall the toolkit..

Anyway i think I solved in another way, if I'll have trouble i can try that way! Thank you

Hi!

I need to implement a temperature control by changing the voltage of a power supply connected to a heater.

I don't have PID toolkit, but I know how PID theorically works.

Attached: VIs (Untitled 1 the principal one) [cannot upload zip file]

Any suggestion, help or hints are appreciated.

Thank you

Untitled 1.vi

HP6XXXA.LLB

ni435x.llb

ni435xcm.llb

NI435Xu.llb