Incorrect reading on some of channel in analog input differential mode USB-6008

[jjichoi]

I have 3 USB-6008 DAQs.  All of them appear to be exhibiting some sort of error in reading voltage.

I am using Windows XP Pro, NI Datalogger (v7?).  I have NIDAQmxBase 1.5 also installed. 

My problem is that I am not getting values that I expect.  I am trying to read the value of 1.5 volt AA battery.

Of the 3 units (USB-6008) that I have, first unit, channel 1 does not read proper values but channel 2, 3 and 4 works fine.  On the second unit channel 1 and 2 gives me incorrect values while channel 3 and 4 works fine.  On the third unit, all channels give me incorrect values. 

For the incorrect values that I am seeing, some seems to be offset issue where it is -1.0 when it should be 1.4 while other channels just gives me completely incorrect values (jumping around as if nothing was connected).

Here are things I have tried:

1. Removed the connectors and attached the leads directly to the unit.

2. Tried different batteries and used multimeter to confirm correct values.

Also, I have not connect the leads incorrectly (I checked multiple times).

Is this a calibration issue or are my units busted?

[Lorne H.]

jjichoi,

What pins do you have your signals connected to(AI0, AIGND, AI8...)?

What do you have selected as your input configuration (Differential, RSE, NRSE)?

Your devices might be busted, but it is very unlikely that all three are busted at the same time (unless subjected to something bad).

It sounds like you might be trying to measure your signals in differential mode with an RSE wire connection.

Lorne Hengst
Application Engineer
National Instruments

[jjichoi]

I am using pins +/-AI0,1,2,3 and all in differential mode.
I don't see how my signals can be RSE.

[Lorne H.]

jjichoi,

Where are your ground lines connected (AIGND, AI4,AI5,AI6...)?

In differential mode the signal line must be connected to AI0 and the ground line must be connected to AI0's differential pair (in the case of the USB 6008/6009 AI0's differential pair is AI4).

In RSE mode you connect your signal line to any AI pin and the ground line to AIGND.

Lorne Hengst
Application Engineer
National Instruments

[jjichoi]

So there are 16 lines for analog and 16 lines for digital.  I am only using the analog part so far.  Following is the pins I am using for the differential singals

| GND | AI0 | AI4 | GND | AI1 | AI5 | GND | AI2 | AI6 | GND | AI3 | AI7 | GND | AO0 | AO1 | GND | or
| GND |  + AI0 -  | GND |  + AI1 -  | GND |   + AI2 -  | GND |  + AI3 -  | GND | AO0 | AO1 | GND |

So I am using pins AI0 and AI4 for channel 0 (AI0 signal and AI4 ground), AI1 and AI5 for channel 1 and so on. 

[Lorne H.]

jjichoi,

It sounds like your USB-6008s are damaged.

I would recommend calling us up at (888) 280-7645 to find out about repairing your devices.

Lorne Hengst
Application Engineer
National Instruments

[jjichoi]

Thanks for your help.