DAQmx usage for multiple channel read across multiple cards

[Silverfang-]

Hello everyone,

I am trying to use the DAQmx to read all the channels of my PXIe chassis. I have 2 1085 racks with same PXIe4300 AI cards in all slots. I tried to list all the channels in the physical channel input and when I tried to read, it showed me an error about syncing timing across multiple devices.

It doesn't show me this error when I read channels from the same card so I am guessing it is something to do with time syncing across different cards? Is there a way to set up the timing to read all the channels on different slots and different racks using the same DAQmx task? 

P.S. I am fairly new to LabVIEW 😄

[ZYOng]

From Easily Synchronize and Trigger NI-DAQmx with Channel Expansion

A task can include channels from multiple DSA, SC Express, and X Series devices given the following conditions:

• The devices must be in a single chassis, and the chassis must be identified in NI MAX.

So you would need separate tasks for each chassis. Search for "4300" in Synchronization Explained. Since NI-4300 does not have any PFI ports to route the trigger signal, you would need another module. PXIe-6674T has the best performance.

[santo_13]

The correct way to synchronize across multiple chassis without timing and synchronization options is to use a 6674T card on each chassis to externally route the triggers.

[Silverfang-]

Thank you for your reply!

Just a follow up, I don't have the 6674-T and I don't think we accounted for it in purchasing. I am okay with segregating my applications and using different tasks for each chassis because the purpose of each chassis is different so that's fine.

In such a case, the master slave synchronization would be enough right?

(I could test this to verify but I don't have access to the rig over the weekend hence just throwing it out there =))

[ZYOng]

If two chassis are not connected by any means (Timing & Synchronization upgrade, any DAQ device with PFI, or PXIe-6674T), you cannot route any signals between the chassis and do any forms of master-slave synchronization. There are only two separate masters.

[Silverfang-]

Just to clarify, I am using 2 PXIe 1085 chassis with a single 8840 quad core CPU in chassis 1. The two chassis are linked using a PXIe 8384 MXI express X8 module on each chassis.

So does all this hold true for this case as well?

[ZYOng · Accepted solution]

---

@Silverfang- wrote:

Just to clarify, I am using 2 PXIe 1085 chassis with a single 8840 quad core CPU in chassis 1. The two chassis are linked using a PXIe 8384 MXI express X8 module on each chassis.

So does all this hold true for this case as well?

---

MXI device is not capable of routing trigger signals.

PXIe-1085 has two SMB connectors labeled with IN and OUT at the front that allow you to route the 10MHz between chassis. However, synchronization requires either:

• sharing of sample clock
• sharing of reference clock (10MHz clock) and a start trigger.

Although PXIe-4300 has two PFI lines but they are only for digital input and cannot export signals.

PXIe-8840 QC has a SMB Front Panel Trigger that might be able to export the signal. You can try to call DAQmx Export Signal (VI) to export the Start Trigger to /<hostname>/TRIG_SMB of controller in the master chassis (Reference: Use SMB Connector on PXI(e) Controller to Route Trigger Signals), then import the trigger using PFI of any PXIe-4300 in the slave chassis. 

[santo_13]

---

@Silverfang- wrote:

Just to clarify, I am using 2 PXIe 1085 chassis with a single 8840 quad core CPU in chassis 1. The two chassis are linked using a PXIe 8384 MXI express X8 module on each chassis.

So does all this hold true for this case as well?

---

yes, it is still valid for your setup. The MXIe card is used for communication and not synchronization.