NI 5112 card fuction

[nyborn]

Hi:

Atttached is my files. I would like to ask what wrong with my NI5112 card. I used DMM and Tektronics scope to measure the DC Power Supply Voltage. They both give me very close values of 8.81V (DMM) and 9.2V (Tekronics Scope). How come the NI 5112 card give me

8.2V. Could you tell me tell me why and how to solve this problem. I found the device that I measure in manufacturing area are greater than 4.6V, but I used the 5112 card in the computer, it give me 4.2V mostly that the cause the test fail.

I am in a very urgent. I appreciate your quick reponse

[nyborn]

I don't understand why I can not send a file in attachment. Do you have an email address so that I can send?

Or you can image a stright graph of 8.2V in Soft Front Panel and 9.2V in Tekronics oscilloscipe. The DMM reading is 8.81V.

[nyborn]

I don't understand why I can not send a file in attachment. Do you have an email address so that I can send?

Or you can image a stright graph of 8.2V in Soft Front Panel and 9.2V in Tekronics oscilloscipe. The DMM reading is 8.81V.

[nyborn]

don't understand why I can not send a file in attachment. Do you have an email address so that I can send?

Or you can image a stright graph of 8.2V in Soft Front Panel and 9.2V in Tekronics oscilloscipe. The DMM reading is 8.81V.

[Minh T.]

Good morning nyborn,

Thanks for contacting National Instruments with your issue, we'll try our best to resolve it for you as quickly and efficiently as possible. 

What is the expected value you should be seeing?  Since DMMs are specifically designed to measure voltage levels I assume it's safe to treat that value (8.81V) as the reference value we should be expecting.

Since I can't see your screen captures, I just want to confirm that since you're measuring a DC voltage you have it set to DC coupling, immediate trigger etc.  How many volts per division?  I just used one of our Function Generators to generate a DC voltage and read it from a PXI-5112 without any such issues.

The other important factor to look at is the Input Impedance setting for the 5112.  You can set this in the Soft Front Panel by going to Edit > Device Configuration and selecting the Channel tab.  Set the input impedance to 1M Ohm.

Please remember that the 5112 is designed to measure high-speed waveforms at 8-bit resolution, it had not been optimed for extremely accurate static voltage measurements.  For such measurements National Instruments offers the NI-4070, 4071 and 4072 series of DMMs which offer up to 24-bit resolution.

Sincerely,
Minh Tran

Applications Engineering
National Instruments