fluctuating data

[tkdnutter@yahoo.com]

Dear Everybody

I have a PCI6052E board and a SCB 68pin connector block and an output from a signal conditioner. When I use MAX after connected the data in differential format. I am getting the strangest readings from MAX. I know they are strange as i have compared them to what I am seeing on my oscilloscope. 

To connect the signal from my signal conditioner I am using a BNC cable that I have split and I have the positive side going into pin 68 (ACH0) and the negative pin going into pin 34(ACH8).  When I run the MAXtest panel for the PCI board I am getting the strangest reading as follows even though I have not connected to channel 3 and 2 I am getting the strangest fluctuations.

I think that there is a problem with my PCI board, How can I check it? Oh by the way the amplifier is battery powered, do I need to ground the signal??? If so how can I do it. I read that if the impedance is low then the signal may not need to be grounded.

Please help me

Thanks

[tkdnutter@yahoo.com]

Oh sorry i forgot to send you the information about the readings from the PCI board even with the amp turned off. Here is the screen shot

[johnsold]

You may need to provide a conductive path to AI Ground to allow bias currents to flow to the inputs. There is information in the manuals about the details. This is mostly seen in differential connections. With your battery powered amplifier it is quite possible that the bias current path does not exist.

Lynn

[Brian F.]

Hello. 

There are a few things that I would recommend trying.  After trying johnsold's suggestion, I would also make sure that in MAX, you have differential selected as the input configuration.  Also, I would test other differential pair channels such as AI1 and AI9, AI2 and AI10, etc.  Additionally, can you measure the voltage on a simple battery to test the performance of the card?  If so, are the results accurate?  Finally, do you have any other PCI DAQ cards that you could test?  If one DAQ card works while the other doesn't under the same configuration, it is definitely a good indication that something is wrong with the card. 

Have a great day!

Brian F
Applications Engineer
National Instruments

Message Edited by Brian F. on 03-15-2007 10:43 AM