Data Processing from Voltage/Current measurements

[jh5638]

Hi, I wonder if anyone can help with a problem I am struggling with? I am using labVIEW 8.5 with the full developer suite.

I have a set of data with voltage on the scale of micro volts, and current in the 1-2000 A range. Where I am struggling is taking the log Voltage versus log current data, then extracting the data from 10 to 100 micro volts and finding the gradient of just this section.

So far I can aquire the data, then I convert the array to a cluster and (i think) extract the voltage and current part of the signal. I then build this into an array, take the ln10 of the array and display in a graph.

So is there a simpler way of doing this? How now do i extract just part of this data and take the gradient of it? I can't seem to find any useful examples of this!

Thanks

Jon

[Ian Colman]

Hi Jon,

Could you perhaps attach your VI in a reply to this post? It would be allot easier to help you if I could take a look at your current method of doing things.

Regards,

Ian Colman
Applications Engineer
National Instruments UK & Ireland

[jh5638]

Hi, I probably could do, it is just a big hassle as its a non-networked computer with no Internet access, and a nightmare of an IT policy! However if this the best bet I could have a go?

I was more just wondering whether there is a way of getting the program to pull data from an array from points where the data passes certain values (i.e 10 and 100 micro volts) rather than just extracting say from row 50 to row 100? Then taking the gradient of this?

Thanks

Jon

[Ian Colman]

Hi Jon,

Without your code it is hard to make an example because there are several ways of implamenting this but one way you may approach this is to use the loop itteration terminal to index an array in multiples of 50 as shown in the attached image.

As for the gradients, given this data it shouldn't be difficult to use the matmatical operations within labview to process this information but let me know if you run into any difficulty.

I'd be willing to take a look at your code if you can attach it, it is up to you. You wouldn't have to attach the whole project, just the VI where the array input is present should be sufficient.

Best Regards,

Ian

[jh5638]

Right I have attached part of my VI.

To explain (from the left) the voltages are aquired from the DAQ assistant, then the voltage is extracted from the time/voltage array. This is the placed into a new array with the corresponding current reading (from the global numeric) and auto indexed.

Then when the voltage level reaches a certain point the logging stops and ln10 is taken of the voltage and current.

Then the voltage and current are seperated again, the voltage array scanned for 10 and 100 micro volts and these index points taken, as well as the length between them.

Then the sub arrays are indexed according to the aformentioned points and put into an XY graph.

So will this work? Should it be improved?

To get the gradient should I use NI_AALPRO.lvlib:derivative x(t).vi on both the X and the Y data, divide X by Y to give dX/dY and take the mean? Will this work, is there a simpler way? Do i have to use that particular VI? What do i need to put in the initial and final condition and dt for it to cover the whole array i wire in?

Thanks

Jon

[jh5638]

Any ideas at all?

Jon

[Ian Colman]

Hi John,

How are you getting on with this? Does it work? If you are still having difficulty I would appreciate it if you could attach your VI and then clearly state what you wish to achieve that it is not doing already. I'll be happy to do all I can to help but at present I am unsure as to where you are with this and what exactly you wish to do.

Thanks,

Ian

[jh5638]

Hi!

Thanks for the offer! At the minute I have written a program, and I'm going to start testing it over the coming weeks! If I get any unexpected problems I'll report back! Just keeping fingers crossed at the minute!

Thanks

Jon