how to measure the inductance with a ELVS board

[jingrui]

Hi,

I am a graduate student and working on a project. In this project, I need to measure the instantaneous inductance which keeps changing. And I only have a ELVS board and LabView 7.1 in my lab. So does anyone know how to use them to measure the inductance? I really appreciate your help.

Thanks

Jingrui

[Hani R]

Hi Jingrui,

What version of NI-DAQmx and NI-ELVIS do you have installed?  If the NI-DAQmx and NI-ELVIS drivers are installed correctly, you will have a Digital Multimeter VI found in the LabVIEW functions palette under Instrument I/O » Instrument Drivers » NI ELVIS » Digital Multimeter.  When you place this VI on the block diagram, a configuration window will open up.  You can then select the Measurement Function to be inductance.  Connect one wire to the CURRENT HI pin and one to the CURRENT LO pin on the NI ELVIS for an inductance measurement. 

[jingrui]

Hi, Hani

Thanks for your immediate reply.

Actually I have found the DMM in the ELVS today, and I also want to build a program to use the inductance value that DMM measures as my input signal, but I did not figure out how to do that yet. I wonder if you can give me help on that.

Thanks again and best regards

Jingrui

[Hani R]

Hi Jingrui,

The NI-ELVIS Digital Multimeter VI has a Measurement output which you can connect to other VIs.  I’m not really clear on what you mean by wanting to use the inductance value as an input signal.  What exactly would you like to do with the inductance value (store/output/process)?   Post back with some more details about your application so we can assist you further. 

If you are looking for more general information, there are some great resources available on how to program in LabVIEW.  Check out the LabVIEW Introduction Course - Six Hours and the Complete Data Acquistion Tutorial.   

[jingrui]

Hi, Hani

Thanks for your patience. I am a beginner who just start to learn how to use LabView, so your guidence is critically helpful to me. Let me explain my project to you briefly so that you can get a idea about what I am trying to do.  

 I wanna measure the inductance of a magnetic system, whose inductance keeps changing as I change the reluctance of it.  I am trying to use the DMM to measure the instananeous inductance of this system, meanwhile I want to build a VI program to process the instananeous inductance value. There is a fixed relationship between the inductance and the reluctance, so I want to know the relucatnce by processing the inductance value at a certain time. 

Can you get a clear idea about what I am doing? I hope you can give me more help on this,.  I will go over the resource you gave me in last reply and  try to make some progress on how to program in labview.

Thanks again!

Jingrui

[Hani R]

Hi jingrui,

From what I was able to find about the relationship between inductance(L) and reluctance (Rm), Rm = N^2 / L where N is the number of turns in the coil.  It sounds like all you need are some basic math functions.  You can wire the Measurement output of the DMM VI to a divide VI which you can find in the Numeric palette.  You can navigate to the Numeric palette by right clicking an empty space on the block diagram. 

You can also save the value in a file by using a Write to Measurement File VI.  The documents I recommended to you should provide most of the information you need to create your program.  Post back if you have any questions. 

[jingrui]

Hi Hani

Thanks for your patience again. You are right, my base equation is L=N^2/R, and I obtained a more complicated equation by expressing R with R=l/[uA(x)], where A(x) is the area respect to a variable displacement x in the x direction. By measuring the instananeous value of L, I can calculate the x at this time. And I wonder if I can input my equation into Formula VI in the Arithmetic Function.

And how can I wire the Measurement output of the DMM VI into my equations? I find some VI through the path: Function>>Input\Output>>Instr Drivers>>NI ELVIS>>Digital Multimeter;   Should I use the NI ELVIS DMM- wirte VI to get the measurement output of the DMM?

Looking forward to your reply, Thanks a lot!

Jingrui

[Hani R]

Hi Jingrui,

After placing the ELVIS Digital Multimeter VI on the block diagram, selecting inductance in the configuration window, then pressing ok on the configuration window, you should notice that the Digital Multimeter VI will reconfigure its inputs and outputs.  The Measurement Output (as with other outputs) will be found on the right side of the VI.  You can scroll over to this terminal and wire the output to a Formula Node or a Formula VI.  To create the inputs and outputs on the Formula Node, right click the Formula Node and select Add Input or Add Output.  You can then name the inputs and outputs as I have done.  Type in your formula in the Formula Node but make sure you use correct syntax.  In the image below, I wired the Measurement Output to a Formula Node. 



Notice that the inputs and output of the Formula Node are labelled.  If you need help using the VIs, the LabVIEW help is a great place to read about the details of their functionality.  



Message Edited by Hani R on 12-01-2007 12:29 PM

[jingrui]

Hi, Hani

I can not find the ELVIS Digital Multimeter VI as shown in your reply in the labview functions, so can you tell me where to find it? I find some VIs in the instr driver menu but they don't look like the one in your reply.

Thanks a lot!

Jingrui

[Hani R]

Hi Jingrui,

If you have an older version of NI ELVIS installed you will not have access to the Express VIs (like the Digital Multimeter VI).  You would have to use the low level VIs that you are able to find in the Instrument Driver palette.  The image below demonstrates how to connect the data to a Formula Node VI. 



The NI ELVIS DMM - Read VI will output an Array of data corresponding to the different types of measurements.  I am removing the fifth element of the array (index 4) which is the inductance data.  The NI ELVIS help file contains the details about the low level VIs. 

If you want the Express VIs on your machine, you can download the latest version of NI-ELVIS.  Just make sure you have NI DAQmx 8.1 or later installed first.  


Message Edited by Hani R on 12-03-2007 01:27 PM

Message Edited by Hani R on 12-03-2007 01:28 PM