cabling of ground to BNC-2090

[Jiri_2]

Hi,

I have some doubts how ground is connected in the National Instruments BNC-2090 connector block. I use this block with PCI-6221 board. Please, can somebody tell me where is grounded

  - DGND1

  - DGND2

  - GND

  - outer pole (shiled) of BNC connector USER1

  - outer pole (shield) of BNC connector USER2

Thank you

Best regards

Jiri

[lrallen]

Jiri,

The 2090 comes configured for floating measurements in differential mode.  There is a jumper inside the case that can connect the shield of the 2090 to DGND through a 100 Ohm resistor or directly.  See the 2090 User Manual at the link below for more detailed explanations and instructions for grounding options depending on your desired configuration.  Let me know if you have any further questions. 

http://digital.ni.com/manuals.nsf/websearch/B25C39693232E88C8625665E0063596D

Regards,

L. Allen

[Jiri_2]

Well, I know that but it is not exactly the information I need. My problem is following:

• I need to use 5 channels in total (1 AI, 2 AO, 2 DO lines); AI and AO must be in differential mode
• I need to get the two digital outputs into BNC cables, so I made the cabling in the BNC-2090 terminal block to connect DIO0 to USER1 and DIO1 to USER2
• surprisingly, the (optically isolated) instrument connected to USER1 worked well, but not so that connected to USER2
• the difference is not in the signal itself, but in the ground (the signal is output well in the BNC pin of both USER connectors). While the "shield" of USER1 is grounded somewhere in BNC-2090, the shield of USER2 is not grounded
• I found that the shield of USER1 is connected galvanically to DGND1 pin of BNC-2090 and this one is grounded somewhere. USER2 is connecter to DGND2 terminal of BNC-2090, but this one is not grounded.

Sure, I solved the problem quickly by connecting the DNGD1 and DGND2 pins. But still, I have question what is the wiring of GND, DGND1 and DGND2 pins of BNC-2090 and how it should be used.

Thanks

Jiri

[thomson]

The shell of the USER 1 BNC is connected to the DGND1 spring terminal and pin 15 of the 68-pin connectors.

The shell of the USER 2 BNC is connected to the DGND2 spring terminal and pin 39 of the 68-pin connectors.

When the BNC-2090 is connector to an MIO device, pin 15 and pin 39 of the 68-pin connectors are shorted on the MIO device.

[Tom_W_[DE]]

HI All-

One additional consideration beyond thomson's information arises if you are using an M Series device.  For E Series, pins 15 and 39 are both designated as DGND on the DAQ device and will be shorted.  The additional functionality of M Series turns pin 39 into a digital line, P2.7.  So, if you plan to use the BNC-2090 with M Series you will need to short DGND2 to another available ground pin for proper referencing.

Hopefully this helps-

[Jiri_2]

Yes, your answer helps me (I have M-series board). I have shortened DGND1 to DGND2 and everything is O.K.

I have another question: to which pin of board is connected the pin "GND" in the spring terminal?

Thank you

Jiri

[Tom_W_[DE]]

Hi Jiri-

The "GND" pin is grounded to the terminal block itself.  It does not connect to any ground pin on the DAQ board and should not be used as a measurement ground.

Thanks