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speed to acceleration

I am trying convert a speed function into acceleration i have added a sample of the program. I tried some of the derivate function but i dont seem to get the results as i calcutaled it should be between 0 and 20.

 

The signal i want is from RPM then i tried to derivate with just the derivate function thatcan be found in he simulastionfunction then i triedto use the other to derivate function. And i just used and input and output.No time function added.

 

Someone have atip how to make it showme me acceleration function in a graph?

 

 

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Message 1 of 13
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Derivative x(t).vi should do the job. It is not really apparent what you are trying to accomplish from your VI or what kind of data you have. Either use the mentioned VI or programm the derivative/difference yourself. You also have to connect the dt to get the correct values - I guess it will be the reciprocal value of your sampling frequency. Also count that if you perform twice the derivative you wil get a really really noisy signal. In addition if you have an angle sampled signal (which doesn't seem to be your case) instead of time sampled then the computation gets slightly more complicated since then for example a=dv/st=dv/dfi * dfi/dt. Maybe post simple VI just with your data and the derivative method you used.
LV 2011, Win7
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Message 2 of 13
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 oI will try to use the derivate.vi you recommenedbut the problem is cani use the time function i made to put that directcly into the dt? if not then what?.

 

I am new at labview so just bare with me:9

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Message 3 of 13
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What do you mean by the time function? The time sampled signal? Well you don't have to use the dt connector but then it doesn't reflect your sampling frequency and assumes you have the dt=1. So basically you would get the correct shape of your derivative but the amplitude values wouldn't match then.
LV 2011, Win7
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Message 4 of 13
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ok. I can try to xplain what i am trying to build here.The ysstem you are looking at is a hydraulic transmision software. It gets inputs signal from 2 presure meter 1 THACO meter and 1 potensiometer. From that one can have a auto function of regulating the handel of the pump system .

 And the pump system at the and is driving a swingwheel

 

What i am trying to find out is how much acceleration it has when it reches its max point which is 1470 RPM and when we slow it down tillit stops.

 

So do i need to set a input on dt for this

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Message 5 of 13
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Alright so you have the voltage from the tacho sensor, right? You are acquiring the voltage with some sampling frequency, right? So just use the reciprocal value of the sampling frequency as the input for dt. Do you use the Daqmx timing.vi? Look at the examples shipped with LabVIEW. HELP-Find examples... -Hardware input output-DAQmx-Analog measurement-Voltage-Acg&Gph Voltage-Int Clk.vi. I would also use some everaging methods to smooth the signal after the derivative.
Message Edited by ceties on 06-01-2009 05:24 AM
LV 2011, Win7
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Message 6 of 13
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you are correct.Could u ..and onlyif you could show it to me+ i am still not 100% sure what to do
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Message 7 of 13
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To make it clear are we talking here about the angular acceleration as defined here? If so the attached VI should do the job. It acquires the signal and when you press the stop it computes the angula acc. If you would like to see it 'realtime' you would have to modify it a bit. Btw sorry for the confusion in my first post - I thought you have postion signal and you want to get the acc from it.
Message Edited by ceties on 06-01-2009 08:03 AM
LV 2011, Win7
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Message 8 of 13
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how od i modify it if i want to see it in real time?
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Message 9 of 13
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Use the PtbyPt (point by point) version of the derivative and put it inside the loop so it will perform countinously.
LV 2011, Win7
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Message 10 of 13
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