analog input issue with the pci-7332 and umi-7774

[dg_lbe]

Using a pci-7332 in combination with the umi-7774 for driving a stepper motor.  Have an issue with the analog input being 0.488Vdc off from the actual reading.  I've tried several voltage sources only to have the same issue.  I've even used the sample code provided by NI app engineer (found on discussion board analog input issue with the pci-7332) and no result.  What could be the reason for the offset?

[Cameron-T]

What is producing the signal that you are gathering (ie. encoder)? Have you checked the reading with a DMM? What pins do you have it wired into? It could be a grounding problem that we are seeing. Is it a positive or negative offset?

[dg_lbe]

Have wired to 1 ain and 6gnd. Have used dvm. 2 power supplies to verify. Neg offset

[Cameron-T]

For the analog inputs, you should be using pins 32, 33, 66, or 67 for the inputs and pin 68 for the Analog Input Ground. You are probably seeing the consistent offset because you are using digital ground. See the Analog Inputs and Pinout Diagram in the PCI 7330 User Manual found here.

[dg_lbe]

Using the umi interface that connects to the pci 7330. The connections are to analog input of the umi interface

[Cameron-T]

What is the voltage you are expecting to receive? The reason I ask is because I was looking into this behavior and trying to find a simple way to correct it. In my search I found that for the PCI 7330 boards, using a range of -10 to 10 V, you get a resolution of 0.004885 V. This is two orders of magnitude off from what you described, but could be related to the issue you are seeing. You could try changing the range to 0-5 or -5 to 5 or 0-10 to see if it makes a change. I realize this might not be the cause, but the similarity between the value you reported and the resolution seem more than coincidence. It would be worth checking.

[dg_lbe]

Have range set to 0-5v. Tried all ranges without success.

[Cameron-T]

Have you tried wiring your imput directly to ground? If you still have the offset then, it is probably something with either the UMI or the Controller.

[dg_lbe]

I still have the offset.  I performed a continuity test from the UMI- 7774 to the pci-7332 board components.  Its something internal.  Please help........

[Joel-P]

Hello dg_Ibe

I am unsure of what pins you are checking the continuity on, are these the analog input pins? Also, you are you checking the continuity of the cable, or what are you checking between the UMI and the PCI board?

I would appreciate some clarification in order to help you more efficiently.

Thanks,

Joel