Problem with NI 6221

[Dimon87]

Hi. I use one analog output channel and 5 input channels. They all are scanned. When I work only with one output and input chanels (4 channels are not connected), I can see on them the same signal as on working channel.
I read the following issues:
http://digital.ni.com/public.nsf/websearch/B9BCDFD960C06B9186256A37007490CD?OpenDocument
http://digital.ni.com/public.nsf/websearch/4E9B8B3F8FD3A31B862562B5004EA1D9?OpenDocument

I want to understand, what are the solutions of my problem?

What is the source impedance - выходное сопротивление источника?

Thank You.

[Dimon87]

I forgot. I use RSE (not differential inputs). How are they connected in NI 6221?
May be I have to connect the second input from two to ground?

[TCPlomp]

This is normal behaviour. The 6221 has a multiplexer witch switches the input channels of the AD converter.
A residual voltage will be present at a floating input.
Ground non-connected inputs and you will be OK

Ton

[Dimon87]

You mean, that I have to connect with ground other 11 input channels. (5 channels are connected allways and I work with them all but sometimes I work only with one or two channels)

[TCPlomp]

Floating inputs are bad inputs!
But I usually only ground the first floating input, that will do most of the time.

Ton

[Dimon87]

The decision is not to use floating channels?

floating channel - sometimes connected channel, sometimes disconnected?

[TCPlomp]

A floating channel is a channel that is not connected, just ground it when you pull of the signal.

Ton

[Dimon87]

Are these floating channels set in the scanning list?

[TCPlomp]

No, I mean phisical, if you remove the wire from your connection board, you have a floating input, connect this input to the ground via a terminator or something.
That is enough.

Ton