SHC68-68-RDIO/RMIO impedance and termination suggestion

[tikir]

Hello,

there are some informations regarding characteristic impedance for the SH68-68-EP Cable, see:

http://digital.ni.com/public.nsf/allkb/36220E8F02BF21288625686900766E27?OpenDocument

We would like to get similar specs for the SHC68-68-RDIO and  SHC68-68-RMIO, because we need correct terminations for avoiding spikes and reflections.

The static differential output resistance of the driving PXI7833R was measured as 80 Ohms approximately. 

Thank you in advance!

Regards, Timo

[tikir]

Hello,

hmm, no response during one month, neither in the forum, nor by the NI support directly.

Does NI not know, what they sell?

Timo 

[TroubleTheShoot]

Hi Timo,

first of all sorry for the delay in my answer. It took me a while to get the information but finally I got some numbers for you:

The SHC68-68-RDIO specification is 90 ohms.
The data for the SHC68-68-RMIO wasn't quite as clear, but it looks like the AI differential impedance is
about 66 ohms and AO is 107 ohms. 

As mentioned before, the cables and R Series devices have different impedance values.  As a result,
even though the cable's impedance may be matched, there could still be some reflection. 
The signal type and accessory used will all have an effect. 

The best solution will be to have a high impedance load and experiment to find
the setup that minimizes reflection.  If there are any more questions or I can help with anything else,
just let me know. 

Best regards,

David