Voltage Measure, detection fail

[crossrulz]

You have to have LabVIEW FPGA in order to create a bit file that can be used on the PXI-7831R.  DAQmx will not work with it.

[Duplessis]

Ok i have created a VI for the FPGA target (see below).

The problem is that it is sending me absurd voltage values of minus several thousand volt whereas i'm sending a constant low voltage signal. (although the signal change when I change the voltage)

I've linked the Ai0+ and the AI0GND  field of the SCB.

[GerdW]

Hi Duplessis,

please read the manual. Everytime you explore a new application/option of LabVIEW…

The readings look quite ok: you get RAW values from your DAC. -30110 is somewhere near the lower measurement range of your DAC. You need to scale by the voltage range used…

Or you change the reading node to provide you already scaled values, using FXP as datatype!

[Duplessis]

Hi, hank you again for your answer

>

please read the manual. Everytime you explore a new application/option of LabVIEW…

The thing is that i just don't know which manual to read (the one the connection block,  the one of the chassis, the one of the DAC, the one of the FPGA, various Tuto about labview etc...) and often there are even several manual about one thing , I've partially read several for them but i rarely find them usefull and some of them are pretty long especially if considering that i'm not that good in english.  (I've spent 2 days trying to solve a problem by myself, whereas I quicky got relevant answers here) 

What do you mean by voltage range scale? I believe that you are not speaking about the scale of the graph, and there is no way to modify the property of the node.

It seems that there is not FXP datatype on labiew 8.0 and I have no idea of which node measuring if not the node receiving the voltage on the

[GerdW]

Hi Duplessis,

The thing is that i just don't know which manual to read

All of them 😄

As you have problems with the values you receive from your FPGA I would read the manual, that describes the use of that module/card with LV-FPGA…

It seems that there is not FXP datatype on labiew 8.0

Yes, I guess this is a huge problem… Can't you upgrade to a more recent version? (You're ~10 versions behind…)

What do you mean by voltage range scale?

Your AI channel can read voltages in a certain range, I guess ±10V. This reading is given in ADC steps from -32768 to +32767 (I16 range) and you have to scale this range to the voltage range the AI can handle: U = reading * 10 / 32768… (I guess this is described in the LabVIEW help too.)