topic Re: Diffrence between two data from data aquisition in LabVIEW

Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 20:19:36 GMT

Hi,

I got a data aquistion system which is supposed to keep aquiring data unitl the difference between two points reached some big number. For example, I am getting voltage(mv) like 2.31, 2.32, 2.34. 2.33, 2.32, 2.32, 2.33......Until the data reach some point, let's say 0.1V higher or lower than the first one.Thewhole procss stop. Thank you for any suggestions.

Re: Diffrence between two data from data aquistion

MattBradley — Tue, 24 Feb 2009 20:44:53 GMT

Try this... (Labview 8.2)

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 21:02:23 GMT

Hi Matt,

Thank you for your help. However, I do not the Max until I actually run the program. For example, the data I got is 10% bigger than the first one, then the aquistion stops. :(...However, I do know the first one until I run the program.

Em..I kindof see your point. Thank you. Let me work on it...Thank you~~~~~~~~~~~~~~~~~~~~

Message Edited by oly on 02-24-2009 03:02 PM

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 21:36:19 GMT

Hi Matt,

I understood the program now. One more question is I do not know my initial value until I run the DAQ system. The first data I aquired should be my initial value which has a wild range actually, 0-600mv. However, I max difference I want is around 10mv. Any idea how to set the initial value. Can I somehow run my DAQ several times and then get mean of them and then set it as the initial value?Thanks.

Re: Diffrence between two data from data aquistion

RavensFan — Tue, 24 Feb 2009 22:18:06 GMT

It looks to me like Matt's example took care of that. The first (0th) iteration of the loop can't stop while while loop because he requires the condtion and the i terminal to be greater than zero in order to stop the loop. This gives the loop an opportunity to seed the shift register.

Post your code if your having problems.

If you want to get a handful of values and average them to get the initial value, I would just do another DAQ read in a loop of let's say 10 times and feed the average to the left hand shift register to initialize it.

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 22:49:24 GMT

Hi Ravens,

Thanks for your explanation. You and Matt are right. Here is my program.

Couple questions came up. The amplitude I got from the DAQ is dynamic data.

1. Any way to record them and then manage them real time? Is it possilble that we store them in an array or something as Amp(1),Amp(2), Amp(3)..,...Amp(i)?

2. I failed to wire "amilitude" to the wait loop and replace "get data"...I know the data types are different.How can I change the data type of "amplitude"?

Thank you for your explanation again.

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 22:59:59 GMT

I cleared out the seconde question. I used the dynamic data type converter and change to it DBL. I finally connected this two together. 😞

Thanks.

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 23:15:48 GMT

Updated program..

Message Edited by oly on 02-24-2009 05:15 PM

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 23:19:04 GMT

I think I figured it out. The last message is the updated program. Thank you both～～～～～～～～～

Re: Diffrence between two data from data aquistion

oly — Tue, 24 Feb 2009 23:25:45 GMT

Hi,

I am still curious about this one,

The amplitude I got from the DAQ is dynamic data.

1. Any way to record them and then manage them real time? Is it possilble that we store them in an array or something as Amp(1),Amp(2), Amp(3)..,...Amp(i)?

Any idea? Thanks!

Re: Diffrence between two data from data aquisition

RavensFan — Wed, 25 Feb 2009 15:09:00 GMT

I'm not sure what you mean by real time.

If you get a waveform out of your DAQmx Read, you can use Get Waveform components from the Waveform palette to unbundle and get the raw data Y array.

With a dynamic data type, you have the blue express VI conversions. You are using one now to convert from the blue wire to a scalar. If you right click and do properties, you can select various other outputs such as arrays, waveforms, arrays of waveforms, ....

Re: Diffrence between two data from data aquistion

oly — Fri, 27 Feb 2009 07:53:32 GMT

Thank you, Ravens.

I tried to wire Amplitude output with a 1-D array. However, only the first item in the array was keeping changing. All others are still zeros...I must have done something wrong.

What I tried to do is to store all the data from DAQ system into an array. Then later on, I can operate data in the array just like what we do in C or Matlab. For example, if we can store data in an array A[4]= (1, 2, 3, 4), after that, I can get any data out of the array by referring A[1]...A[4]....I am just wondering whether LabView can do this...Thank you!

Re: Diffrence between two data from data aquistion

RavensFan — Fri, 27 Feb 2009 14:10:53 GMT

Of course. LabVIEW has the Index Array function to be able to access individual elements of an array.

We'd have to see your code to give any more help.