ni scope read vi significant figures

[Throggdor]

Hello everyone,

Let me start by giving you some background.

I'm trying to measure a RMS voltage (around 1.8V) using the NI-Scope Read Measurement Vi, which works fine, my problem is that I'm also trying to calculate the RMS current within the same Vi, using a known resistance. Problem is with the voltage I only get two significant figures using the NI-Scope Read, which gives me to much of a rounding error when it comes to the current.

So my question is this; is there another stock Vi that I could use to increase the number of significant figures I get or is there a way with this Vi to increase the number of significant figures? Any other ideas are welcome, and thanks so much for your help.

[camerond · Accepted solution]

I'm not sure what this "NI-Scope Read Measurement Vi" is, but how many significant figures did you set your indicator for (right-click, Properties)? If that doesn't help you, please attach your VI.

Cameron

[Throggdor]

Hello Cameron, thanks for your replay

You can find a link to the VI I described below.

NI-Scope Read Measurement Vi

Also attached is the VI I'm using its pretty straight forward, initialize, set, read measurements and then close; with a lot of the options set. I've tried using a few different VI's in the NI-Scope pallet but all of them give me the same results. I've looked at the measurements on the scope soft front panel and those are prefect, I just don't know how to translate those reading into the VI.

Also I wasn't able to figure out what you meant by "how many significant figures did you set your indicator for", I wasn't able to figure out how to do that, could you give me a little more detail or link me to an NI support page.

Again thanks for all the help.

[Dennis_Knutson]

As mentioned,right click on the indicator and select Properties and then go to the Display Format page or right click and select Display Format.

Your indicators are set for 2 Digits of Precision.

[Throggdor]

Thanks Dennis, took me a bit of looking but the part I was missing was what was the indicator, thanks for the help guys I appreciate it.

[camerond]

(Found out the conversation continued while I was typing, just back from lunch)

The "niScope Read Measurement" VI is actually giving you a double-precision answer, which is a lot more than 2 sig. figs (15, I think, could be off a couple).

Look at your front panel, do not start your program.

Move the cursor over one of your RMS reading numbers.

Click your right mouse button.

Go down the menu to "Display Format" (or "Properties", makes no difference, you then just click on Properties tab).

Read: "Digits [2] Precision Type [Digits of Precision]".

Fix.

Cameron

One bit of unsolicited advice.

Since it looks like you may not have tried much LabVIEW programming since you were last here asking basic questions like this one a bit over a year ago, please take some time to go through the online LabVIEW tutorials
LabVIEW Introduction Course - Three Hours
LabVIEW Introduction Course - Six Hours