Reading analog signal thru the backplane on PXI-1052 in niDAQmx

[dcxemc]

I have SUSE 9.3 and NiDAQmx installed on a PXI-1052 with a 6071E in slot 4 and a SCXI-1125 in the first SCXI slot.  I can't read any of the analog channels.  They're just floating.  To make sure it's not the chassis, I moved the controller to a PXI-1010 that has a 6070E in the rightmost slot and a different SCXI-1125 in the first SCXI slot.  Same thing.  The only way I've been able to read the analog voltages is to reconfigure and have the 6070E use the front connector and physically run a cable from the back to the front.  If nothing else, this verified that my C code works.   Either way I must be missing something here but I haven't found anything in the forums, knowledge base or manuals.   What needs to be done to route the analog signal to the backplane?

Here's the current configuration I'm using on the 1010:

[DAQmx]
MajorVersion = 8
MinorVersion = 0

[DAQmxDevice Dev1]
ProductType = PXI-6070E
;DevSerialNum = 0xBA5159
BusType = PXI

[DAQmxSCXIChassis SC1]
SCXIChassis.ProductType = SCXI-1000
SCXIChassis.Address = 0
SCXIChassis.CommDev = Dev1
SCXIChassis.CommModuleSlot = 1
;SCXIChassis.CommMode = PXI Backplane
SCXIChassis.CommMode = Front Connector

[DAQmxSCXIModule SC1Mod1]
ProductType = SCXI-1125
SCXIModule.Chassis = SC1
SCXIModule.Slot = 1
SCXIModule.CabledDev = Dev1
SCXIModule.DigitizingDev = Dev1
SCXIModule.DigitizationMode = Multiplexed

[Ima U]

Hello,

I was reading thru your post and realize that you aren't doing anything wrong.  You cannot route analog signals through the backplane.  You do need to do this through the front connector.  The back plane is used for timing(digital) signals only. 

[dcxemc]

I've read that, but in a number of KnowlegeBase articles I keep seeing things like this:

In either the PXI-1010 or PXI-1011, the SCXI chassis that is integrated into the PXI chassis communicates with a PXI DAQ board through an internal backplane. This internal backplane is what allows you to avoid cabling the front of the PXI DAQ device to the back of an SCXI module in the integrated SCXI chassis. There is one simple difference between traditional SCXI operation and SCXI communications within a PXI-101X system: the integrated SCXI chassis actually uses a channel on the DAQ device that is dedicated to the internal backplane, which frees analog channel 0 on the DAQ device for other things.

and

If you are using the PXI-1010 chassis, slot 8 has connections for a PXI peripheral module to control the SCXI subsystem. These connections use the available local bus right pins (PXI_LBR0:12). The SCXI connection passes communication, timing, and analog signals between the SCXI backplane and the PXI module in slot 8.

If you are using the PXI-1011 chassis, slot 4 has connections for a PXI peripheral module to control the SCXI subsystem. These connections use the available local bus right pins (PXI_LBR0:12). The SCXI connection passes communication, timing, and low-voltage analog bus signals between the SCXI subsystem and the PXI module in slot 4.

I've also seen PXI-1010 chassis around here that appear to be doing this with labview.  Since they've been in use I haven't had the opportunity to look into exactly how they're doing it.   If it is the case that analog signals can't be multiplexed to the E Series DAQ card in the PXI chassis, what is the use for the analog bus that connects between the PXI and SCXI buses that I keep reading about?

The two KnowledgeBase articles quoted above are 20HFBLCR and 16O1D6PV.

Thanks!
Vince.

[dcxemc]

To add to the above, I found this in KnowledgeBase article #2WMDTM5B:


The information in this KnowledgeBase article is specific to programming for Traditional (Legacy) NI-DAQ with a PXI-SCXI combination chassis. Performing acquisition in NI-DAQmx with a PXI-SCXI combination chassis is considerably more straightforward. The operation is exactly as described for externally-cabled SCXI chassis in the SCXI Quick Start Guide (linked below) once the chassis has been properly configured in Measurement and Automation Explorer (MAX).

For Traditional (Legacy) NI-DAQ, when using a PXI-1010* or PXI-1011* chassis, the PXI DAQ device does not acquire using the regular AI channels (for example ACH0 + ACH8 for DIFF channel 0). Instead PXI DAQ device has a special channel that connects to the PXI combination chassis backplane to the multiplexed Analog SCXI bus. This channel cannot be referred to in your program as '0' which is the channel that you would use with separate SCXI chassis and cabled DAQ devices. Instead you must use a special channel string "ND_PXI_SC". You must specify this channel instead of using '0' when specifying the AI channel in your program.

Can someone elaborate on how it's "considerably more straightforward"?  So far I haven't been able to do it on any chassis in Linux with NI-DAQmx.

[Ima U]

Hello,

Upon further inspection of your hardware's manuals I do realize that you are correct.  You are suppose to be able to pass analog signals from the SCXI portion of your chassis to slot 8 in the PXI 1010 or slot 4 in the PXI 1011.  I do apologize for the confusion.  Since we are certain that your cards and code are indeed functional I would advise you to contact technical support to trouble shoot your PXI chassis.  Please create an email or phone support service request at www.ni.com/ask

[dcxemc]

The field engineer is due here tomorrow, I'll see what he can come up with.  As it stands right now, I've tried 3 different chassis (1052, and 2 1010s), 2 8176 controllers, 4 SCXI-1125, 2 SCXI-1102B, 3 PXI-6070E and 3 PXI-6071E.  Pretty much rules out a hardware issue.

[dcxemc]

I thought I'd provide an update in case anyone else encounters this.   The Cabled Device entry in the config isn't supposed to be there if you're trying to read from the backplane:

SCXIModule.CabledDev = Dev1

It already has a Digitizing Device entry (SCXIModule.DigitizingDev = Dev1) which is what tells it to use the backplane.  The CabledDev entry somehow overrides or confuses it.

Hey NI, what would be great is if there was a list somewhere of all of the possible entries and what they mean.

[Ima U]

Thank you for posting the solution to the problem for the benefit of others.  

I hope this helps!

[dcxemc]

I've seen that one.  It contains at least one error that set me back a few days when I first started on this project. 

SCXIChassis.CommMode =

Specifies the mechanism by which the communicator device connects to the chassis.

Options include Front Connector and PXIBackplane.

It's not PXIBackplane, it's PXI Backplane.  That space between the I and the B is important.  Without it nidaqconfig gives an error.

[Ima U]

Thank you for pointing that out.  I will edit the document.