SCXI with USB-6341

[mathispower]

From a hardware standpoint, can a USB-6341 be used to capture data from an SCXI chassis (ignoring the connector/wiring situation)? I would like to use this scenario and program in C++ but the device access is controlled through MAX and MAX doesn't allow the USB device to be selected as a chassis communicator. It is my understanding that M-series USB mass terminated devices could be connected to SCXI so I'm wondering if it is just a list of compatible devices MAX uses and the USB version of the 6341 isn't on the list for whatever reason (which I would be curious to know).

In this note mass termination is called out specifically (for the M-series USB). What is the difference between mass termination and the wiring pin to pin?

I realize I can communicate with the SCXI in other ways but going through MAX would be much simpler for me (especially for calibration/troubleshooting) and I could use the NI provided DAQmx C examples.

Thank you

[LindyHop]

Hello mathispower,

You can not use the USB-6341 to control an SCXI system. For USB connectivity options you can use only non-bus powered M or X series devices with mass termination. Since the 6341 only comes in a BNC and Screw Terminal configuration it can not function as a controller (as you've already noticed by checking in MAX).

[Ckelley]

Thank you for the reply.

What is special/unique about the mass termination versus doing pin to pin wiring? It seems to me from reading the SCXI manual that if I send the right signals to the right locations I can control the SCXI, although I have yet to confirm this.

[LindyHop]

Communicating with the SCXI chassis requires the use of an APFI line. This line is not available on the device you're currently using. In addition, the use of bare wires for connecting would be detrimental to the accuracy of your measurement and is therefore not a supported configuration by NI.

If you don't mind me asking, why do you want to wire the pins directly? NI offers devices with mass termination and the cables needed to communicate with the SCXI system in a supported configuration so that you don't have to spend the development time making your own (eg creating a custom cable that meets industry specifications for noise/safety etc).

[Ckelley]

Unfortunately this is for work I do at home so I'm in the usual predicament of having to spend more time doing things myself where I can't afford to do it otherwise. I thought the device did have the APFI capability when I purchased it.  Accuracy isn't a concern for me because I just need to see the signals (for example: high channel count temperatures where most devices are +/- 1°C on the spec sheets and I just need to know if heat transfer is working properly). I am trying to move away from a DAQcard that I was using for the SCXI to something USB that I can use with any computer in the future.

By the way, I'm only using bare wires inside the X-series enclosure. The cable is an EPM cable and I wired everything per the pinout diagram provided by NI for that cable.  The BNC breakout I have wired to the SCXI chassis was working properly so I assumed it was good to go but couldn't get the device to show in MAX. Now I realize it is just the feedthrough on the 1349 that is working and communcation with the chassis won't work.

Thank you