Synchronization of SCXI modules?

[Rizy1976]

Hi there, New to this forum need help?

Trying to read voltage samples into C data acquisition application. Here is the setup.

SCXI 1143 to 1120D paired (4 pairs).    1120D feeds signals to PXI 6143 S Series(4 modules). PXI chasis connected to PCI card. Total 4mods @ 8 channels = 32 channels.

Previously, referenced to the provided samply apps in NI-DAQ/Examples/DAQmx ANSI C  folder and got system to work with PXI physical channels. Now I need to read samples from SCXI channels to be able to use filtering.

So far here is what I got.

I replaced PXI physical channel names to SCXI physical channel names. It fails on synchronication of module clocks. I skip the sync, then it works fine and gets samples from SCXI.

Now looking at SCXI example C app., it seems that there is no mention about sync as it is in PXI app. The samply applicatoin for SCXI only demonstrates single module/task setup. Ive got multiple SCXI modules therefore I assume synchronization is required.

Please explain how to sync mutiple SCXI modules as I did for PXI using DAQmxCfgDigEdgeStartTrig() call.

Thanks

Riz

Message Edited by Rizy1976 on 01-22-2007 03:13 PM

[David L.]

Hi Riz!

Before I can fully answer your question, I would like to get some clarification on a few items. Are you using separate PXI and SCXI chassis or are you using a PXI/SCXI combo chassis? How are you connecting your chassis to the computer – Are you using a MXI controller, an embedded PXI controller, or connecting through the SCXI chassis? On that note, can you please put a bit more clarification around how you have all of your equipment setup?

 

Not all applications require synchronization - Is there a reason why you need synchronization? How are you trying to route your signals?

[Rizy1976]

Hi David,

Well here is the details. I have SCXI-1001 chasis with four SCXI-1143 modules. Then a sepearte PXI-1036 chasis with four PXI-6143 moduels. Each SCXI-1143 is paired with one PXI-6143 and connected with a cable. PXI chasis is further connected to the PC through a PCI card. My max explorer displays four PXI-1143 and a SCXI chasis with 4 slots taken by SCXI-1143.

Now I need to sync all four SCXI cards together since they all have same data source. I read samples from all of them but they are not sync together. What I have tried using a sync sample program is synced PXI Mod2, Mod3, Mod4 with the left most Mod1 and acquired raw samples from PXI chasis without filtering.

Now I want to use SCXI chasis and use filtering. I read samples from all four SCXI modules by simply replacing the physical address of the modules from PXI to SCXI. 

The problem is that the method used is PXI for sync did not work for SCXI. Use function call DAQmxCfgEdgeStartTrig() to edge Mods 2, 3, 4 with Mod 1 clock. Later when I start communication it retruns an internal error saying.

Failed Start Scan. Error:

Source terminal to be routed could not be found on the device.

Make sure the terminal name is valid for the specified device. Refer to Measurement & Automation Explorer for valid terminal names.

Property: DAQmx_DigEdge_StartTrig_Src

Property: DAQmx_DigEdge_StartTrig_Edge

Source Device: NI6143SCXI1

Source Terminal: ai/StartTrigger

Task Name: NI6143SCXI2

Status Code: -89120

What it seems like to me out here is that I did recognize the device address for Mod1 "NI6143SCXI1" but failed to recognize the terminal name provided for this device. I have tried other terminal names for this device too from the list of terminal names in the documentation. Nothing seemed to work. It seems like SCXI do not have these terminals/internal channels defined.

As a work around, I have synced all four of my SCXI cards with the left most PXI card by providing PXI mod1's device address. But the best way would be to have SCXI being synced on their own.

I hope this explains the problme.

Thanks

Riz

[David L.]

Riz,

Thanks for all of that information! (Especially the error code and description). From what you are describing, I believe you basically want to sample all 32 channels simultaneously, true? One suggestion is to make sure all of you equipment is setup correctly in Measurement and Automation Explorer (MAX) – this article may help. Please notice it says NOT to configure the 1120D (Bottom of DAQmx Software Configuration section).

Also, what is your sampling rate and how long are you sampling for? Lastly, what do you mean by synchronization? Do you want to share triggers in order to start all of your DAQ cards at the same time? Or do you want to share trigger and clocks, so that they not only start at the same time, but all share the clock off of one DAQ card?

[Rizy1976]

Hi David,

Thanks for replying. Yes, I do want to sample all 32 channels together. As far is configuration in MAX is concerned. Im sure I have it setup right. I do manage to get samples from all SCXI channels if I do not try to share trigger to sync the start.

As far as sync, the idea is to have the clocks of all four modules be in sync. They should edge simultaniously which is possible if they are started at the same time with a shared trigger.

There is not issue with physical device address or "/" or anything as talked about in many postings. If device address was a problem with I wouldnt have had any samples at all, not even without syncing.

Right now, I have givent the physical address of my first PXI card to all four SCXI cards for edgeing. Not sure if that would eventually work right.

I hope Ive given you all the information you asked for.

Thanks

Riz

[David L.]

Riz,

I'm including some code that I tested with 2 PXI-6143 and 2 SCXI-1143. Including both SCXI modules with their channels in the same task does automatically enable simultaneous triggering and clock sharing as long as the cards being used are both S-Series.

The configuration of your SCXI system in Measurement and Automation Explorer should be to have each 6143 control each 1143 in parallel mode. Clicking on Details... of each module in the SCXI chassis property page will allow you to specify the cabling connection to each module and verify that they are set up for parallel.

The function for creating the channel should look similar to this:

DAQmxCreateAIVoltageChan(taskHandle,"SC1Mod1/ai0:8, SC1Mod2/ai0:8, SC1Mod3/ai0:8, SC1Mod4/ai0:8","",DAQmx_Val_Cfg_Default,-5.0,5.0,DAQmx_Val_Volts,NULL);

You should be able to use the example located at C:\Program Files\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Analog In\Measure Voltage\Cont Acq-Int Clk and make modifications to it in order to see this in action.