I intend to use a 9181 ethernet chassis and a 9215 quad-Ain module with screw terminal with a cable between the internal 15-pin Sub-D connectors. The PCBs will be outside their original housing, and inside a different device.
My questions: how long can this cable be ? Currently 20 to 35cm are planned - due to space restrictions, it is not possible to have less than 20cm.
Is there anything to consider for the cable ? I am planning on a handmade 15-wire cable with a common shield soldered to both plugs. Should certain wire pairs be twisted ?
And a question aside from the wiring: as this construct will be totally isolated, is there a reason why the reset button should be available outside of the construct, or is a power cycle / ethernet cable plugging cycle sufficient for any issues ?
Thanks and best regards 🙂
the NI 9215 does not come with a Sub-D Conectivity, only Screw- or Spring- Terminal or BNC:
Given the fact, that there is no specific cable desiganted for the use, there also is no limitation specified. However, 35cm should not be a problem regarding Voltage drops. Take a look in the Specifications of a cable:
I believe, the AI+ and AI- Wires are twisted together. Check out these Documents for the benefit of twisted pairs:
Field Wiring and Noise Considerations for Analog Signals - National Instruments
How Do the "Twisted Pairs" of Wires in the SH68-68-EP Cable Affect Single-Ended Measurements? - National Instruments
Regarding the complexityyou could also buy a cable and customize it to your needs, or go with NIs Breakout Cable:
NI 15F-Breakout - National Instruments
The Reset Button doesn't do more than a Power Cycle, so you should be fine building the construct around. There is a functionality, that by pressing the Reset Button longer than 5s, the cDAQ boots with the default factory configuration settings, but usually, you will not need this (page 39):
NI cDAQ-918x/919x User Manual - National Instruments
I hope this helps, best,
thank you for the extensive and informative reply; sadly, the Sub-D connection i was referring to is the 15-pin high density Sub-D in-between the 9181 and the 9215 😉
As mentioned, due to the project's housing space I can only use the raw circuit boards with a short cable instead of a zero-length connection.
[PC & PS] ---- [RJ45 and power connector of 9181][9181 internal Sub-D] ----xx---- [9215 internal Sub-D][9215 screw terminals] ---- [analog signal source]
The ----xx---- above is the connection I am referring to.
This kind of setup is not the intended use and therefore not covered by the user manuals; hopefully someone else out there has already tried something similar and found some interesting ToDo's or DontDo's in that matter 🙂
Thanks and best regards,
clearly there was a misunderstanding, thank you for pointing that out. Unfortunately, what you are trying to do is not only "not supported" by NI, it is also not recommended. The high frequency timing signals could be disrupted by a cabling of any length. Of course you can still do it, but your measurements might not be as accurate as you would expect them, so extensive testing will be a "must".
Good Luck for your Project,