Synchronising USB-6009 and USB-9237

[JRFub]

Hi all,

I have a USB 9237 in a USB 9162 carrier which acquires force measurements from two load cells and I'm trying to synchronise these measurements with displacement measurements from an LVDT connected to a USB 6009. Any suggestions for how I might do this?

Cheers,

Carina

[lucaso3]

Hi JRFub,

Thank you very much for your question. I would like to show you a couple of links that might be very useful for you.

http://www.ni.com/white-paper/11369/en/ 

http://www.ni.com/product-documentation/4322/en/ 

http://www.ni.com/white-paper/6829/en/ 

I really hope this information can be valuable.

Regards,

Luis.

Applications Engineer.

[JRFub]

Hi Luis,

Thank you for your reply. Unfortunately after a little more digging I have found that the USB-6009 and USB-9162 do not support external clocks. It seems that the only option I have is to find some way to trigger the DAQs to start acquisition at the same time (although I understand that there will still be some timing drift that will occur without synchronising the clocks).

Is it possible to synchronise the start triggers for these devices? I can kind of grasp the software side but what sort of hardware changes would I need to implement?

Alternatively, is it possible to synchronise these devices if they're plugged into a PXI-8196 with the SMB Trigger on the front panel connected to the PFI line on the USB-6009?

Sorry for my ignorance but any help would be greatly appreciated. 

Cheers,

JR

[lucaso3]

Hi JRFub,

Probably con can set some triggers by software. Here are some information on the DAQmx Triggering VI that can help you acknowledge which adapt better your application.

http://www.ni.com/tutorial/4329/en/ 

You can try to use the trigger of one signal to star other one. In the previous links you might find some information and on the following, we can complement:

http://www.ni.com/tutorial/11549/en/ 

http://www.ni.com/white-paper/2835/en/ 

Now, regarding the PXI-8196, since this is an obsolete device, I don’t have much information about it. I will need to investigate a little further about how we can try to trigger on the device.

Regards,

Luis C.

Applications Engineer.

[JRFub]

Hi Luis,

I've previously tried to replicate the examples in the tutorials and white papers that you passed along and had no luck. I don't know what to set as the trigger source and the VI will not run without one. I've read somewhere about using a digital output on the USB-6009 and wiring it into the PF line but I'm not entirely sure how that works if I cannot supply a similar source/signal to the NI 9237. 

As an alternative work around, if using a VI such as the one attached with output .lvm files (where Dev2/ai0 and Dev2/ai1 are from load cells connected to the NI 9237 and Dev1/ai0 is a LVDT connected to the USB 6009) can I assume that the time and date for each signal data set is the time and date at which the acquisition for that particular data set started? Then using the corresponding delta_x create timestamps for each data point relative to the "starting" time and date. Following that use interpolation to predict the say the LVDT displacement value for a given load data point? 

For the purposes of this work around, I understand that I am ignoring timing drift between the two devices but do you thing that this would introduce a significant error (e.g. more than 5%?)

Cheers,

JR

[lucaso3]

Hi JRFub,

Yes, I doubled checked and due to your current hardware setup, you cannot use any hardware triggering. If you had any DAQ Chassis, you might try routing internally the signal from one to another, but since they are USB, we cannot do this.

About the code, you are starting the tasks on the same sequence structure, which is the way to do it in software. Unfortunately by doing this, we depend on the OS and the amount of tasks that the computer is running. I cannot assure you that the significant error will be lower than 5%, there are too many factors that affects the system.

Regards,

Luis C.

Applications Engineer.

[JRFub]

Hi Luis,

Thank you for your help. I will look into alternative options. 

Kind regards,

JR