# Digital Multimeters (DMMs) and Precision DC Sources

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## How can I measure the variable voltages with the DMM and Switch?

Hello,engineer ,

I am a student, I want to measure the variable voltages which from V to Via. I have the following hardware: PXIe-1065 PXI-4065 PXI-2529. I use the PXI-8360 and PXI-8361 to communicate with my PC. I hope I can do this when I measure the next voltage I should click the mouse and connect the right position to the measurement object.

How can I realize that?

Any suggestions with great appreciation.

Since I know a little English, if I didn't explain my question distinctly, please ask me.

Best wishes.

Regards.

chuanyuehuoxian

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## 回复： How can I measure the variable voltages with the DMM and Switch?

Hi

I think the key point is that you should know the topologies of switch, so we can use the switch card to swicth UUT to realize auto-test.

I think you can refer to the example of LabVIEW like below, which show how to use DMM and switch to realize auto-test.

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## 回复： How can I measure the variable voltages with the DMM and Switch?

Firstly, thank you very much for the answers.  But I didn't want to realize the automatic testing. Since I need to measure different voltages that I should connect the different position. I just want to achieve that when I connect the first position, I click the button1, the computer shows the result. Then I connect the next position, I click the button2, the computer show the next result. What's more, I want to acquire 100 samples of result so that I can calculate the average of them per every measurement.

Other questions: I may want to acquire 100 results per measurement  just by PXI-4065, can I ?

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Accepted by topic author 穿越火线
08-27-2015 04:09 PM

## 回复： How can I measure the variable voltages with the DMM and Switch?

Yes, you can.

You can set the samples when using DMM.

You can also refer to  the example in LabVIEW.

Thx!

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## 回复： How can I measure the variable voltages with the DMM and Switch?

Thanks, engineer.

I just to try. Thank you.

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## 回复： How can I measure the variable voltages with the DMM and Switch?

Hey chuanyuehuoxian,

Were you able to get your measurements working?  If not, I'll make some assumptions on what you're trying to do:

-you want to measure the voltage at 4 different test points.

-each test point needs to be measured differentially (two wires to the DMM to measure voltage).  You do some research and decide to use the 2529 in a 2-wire 4x32 configuration.

-at each point, you want to take 30 measurements and then move to the next point.

-I'll assume you have 0V on c0, 1V on c1, 2V on c2, and 3V on c3.

The first thing you'll need to do is hook everything up to the switch.

-Pull up the PXI-2529 pinouts in the NI-Switches Help (Available on your machine, and also online here

http://zone.ni.com/reference/en-XX/help/375472C-01/switch/2529_2-wire_4x32_matrix/

-You connect your DMM to r0±

-You connect your four test points to c0±, c1±. c2±, and c3±

With this setup, you can connect your DMM to any of c0:c3.

Next, let's make sure everything is wired correctly:

-open the NI-DMM Soft Front Panel (Start»All Programs»National Instruments»NI-DMM»NI-DMM Soft Front Panel)

setup the DMM to take a voltage measurement. With our assumptions, put the DMM in the 10V DCV range.

-open the NI-Switch Soft Front Panel (Start»All Programs»National Instruments»NI-Switch»NI-Switch Soft Front Panel)

Inside the Switch SFP, set the switch to the 2-wire 4x32 matrix topology.  Then click at the intersection of r0 and c0.  You'll see a thick, colored line, which indicates that you've made a connection between r0 and c0.  With our assumption, you should read 0V on the DMM.

Next - this is very important - click on the connection between r0 and c0 again, and make sure that the colored, thick trace goes away.  This is important because if you connect multiple columns (e.g. c0 and c1) to the DMM at the same time, then c0 will be shorted out to c1.  If you're only taking voltage measurements, I recommend adding 1kOhm series resistance between each test point.  This won't affect your voltage measurement appreciably in most cases due to the high input impedance of the DMM.  It will prevent shorting out test points if you accidentally close multiple columns onto the DMM row at the same time.

So, now with the path disconnected between r0 and c0, next click on r0 and c1.  You should read 1V on the DMM.  Continue this on the other two channels and verify that the hardware is setup correctly.

...

Now that you have everything working using the test panels, it's time to move into programming in LabVIEW.  Open up the Example Finder in LabVIEW (Help»Find Examples).  Once the Example Finder is open, browse to Hardware Input and Output»Modular Instruments»NI-DMM»Multi-point measurements»acq & Graph Multiple Samples.  Open up the Switch Soft Front Panel and make a connection between r0 and c0.  Then run the code (you'll need to configure it to measure 10VDC) and verify that you get a bunch of readings around 0V.  Note that if the DMM Soft Front Panel is still open, you'll get an error when you try to run the VI because two things are trying to access the DMM.  Thus, make sure you close the DMM Soft Front Panel before you run the DMM examples.

Once you're happy with the DMM code (you'll likely need to modify it for your application), let's look at some switching code.  Back in the Example Finder, browse to Hardware Input and Output»Modular Instruments»NI-Switch»niSwitch Making Connections on a Switch.  Select the channels you want to connect (e.g. 'r0' and 'c0') and then press run.  Note: You can keep the switch soft front panel open even when switch code is running so that you can diagnose the switch state.

Let us know what questions you have thus far and we'll continue from there.  Good luck.  Have a wonderful everything!

-John Sullivan
Analog Engineer
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-John Sullivan
Analog Engineer
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