Voltage on graph twice that of input

[catinthehat]

Hi

The input voltage source is showing twice the amplitude on my graph.

Hardware

PCI-6040 with SCB68

Input

500Hz 0-2V sine wave

When I connect the waveform to any of the analog inputs, a 2V input signal shows up as 4.  I have tried my own program, an example from the help, and Ni-Max all which shows the same thing.  I have it set up as a differential input (the other options show nonsense)

Is this normal behavior?  How do I correct this?  I could use scaling but I didn't want to do this until I knew it wasn't something else I was doing wrong or missed.  Shouldn't the AD show 1V for a 1V input?  When I run the calibration in Ni-Max, the input reading is very close to the signal 2V shows 2.035V as an example.  Additional when I input 8V sine, it only reads 6V.

Aside: I also tried a DC voltage, both from a power supply and a battery.  Both show an output of 10 on a graph.  How do I set up ni-max to measure a straight DC voltage?

Thanks for your help

[billko]

It sounds kind of like you are mixing up Vrms and Vpp, and to add confusion, you are also doing differential input...

I would recommend, instead of just guessing at what the input is supposed to be - e.g., "the other options show nonsense", you should revisit exactly what you are trying to do, and how you are supposed to do it.

[altenbach]

It is impossible to solve your problem from a vague description. Can you show us some code? What is dy of the y scale? Could the sine wave be -2 to 2V? What's the frequency?

[catinthehat]

Hi

Using NI-Max (test panel or create task)

The input signal is 0 to 2Vpp at 500Hz.  The output on the graph is 0 to 4Vpp.

The calibration tab under Voltage Input Setup for creating a task using Ni-Max shows the board reading 2V for a 2V input. 

The input signal is generated with a function generator.   Not using a differential input shows nonsense because the grounds of the two systems are not the same.

I used NI-Max under the test panels tab and create task so no code to show.

pete

[catinthehat]

Hi

I used Ni-Max (both under test panel and create task) so I have no code for you.

The input is 500Hz 0-2V, for clarification 0-2Vpp.  The output shows 0-4Vpp 500Hz.  I used a function generator to create the signal, the signal was verified to be  0-2Vpp (using a scope)

I haven't put in any scaling for the x or y axis. 

The board seems to be reading the input correctly  (seen under the calibration tab of Voltage Input Setup in Ni-Max)  but doesn't display it correctly.

pete