Need help setting up cFP-2000 with cFP-SG-140s for synchronized data

[RTPAX]

I'm working on a system that consists of four cFP-2000s plugged into an ethernet hub, which is then connected to a PC, where each cFP-2000 has two cFP-SG-140 modules for reading strain gauges.  My goal is to acquire strain data from each channel of the SG-140s (8 input channels of strain for each module) at the same time step. 

I've been using MAX (Measurement & Automation Explorer) to configure the cFP-2000 and cFP-SG-140s, and LabView (V8.5.1) VI to acquire the data, process the signals, and write the text files with timestamps, but I've noticed now that my data points come in at very different time steps.  I'm entirely new to LabView, so it's taken me two weeks to write the LabView VI to read, process, and write the data for all those channels, but I have a sinking feeling that I should be doing this in LabView Real Time.  Unfortunately I'm completely in the dark as to LabView RT.

I guess my questions are: How do I setup this system to acquire and record the strain input at the same time step (global time and dt), do I need to use LabView RT, and if so, can I utilize the VI code I've already written in LabView RT?

Thanks a lot, and I can post my VIs if necessary.

- Ryan

[Matthew_Williams]

Hi Ryan.  The time resolution on the SG-140 modules is approximately 1 second, depending on the filter setting.

Are you trying to synchronize to less than 1 second?  If 1 second synchronization will meet your application needs,

you should be able to do that using either a PC to just collect data from the cFP nodes or running RT on the nodes.

If you care more about absolute time than synchronization then the timestamps associated with your readings

should be pretty good but you may have to synchronize the clocks on the cFP modules frequently.

Sorry the answer is '... that depends...', but I think the refresh rate of the SG-140 modules may be a limiting factor.

Can you give some more information about what you are trying to do?

Matt

[RTPAX]

Thanks for the reply.

I'd need to get data points at least 10 times per second, but would like to make it adjustable to either more or less data points per second if the resolution is needed. 

It sounds like I should start hitting the books and learning LabView RT, huh?

[Matthew_Williams]

Hi Ryan.  The update rate on the SG-140 is about 1 reading a second, meaning you only get a new value

at that rate.  You can certainly read the IO hardware faster, but you will get identical readings for approximately

1 second, then the next second's worth of readings may have a different value.  Doesn't sound like what you

are after.  If you really need to make 10 measurements a second, I don't think the SG-140 will do what you want.

Matt

[RTPAX]

That definitely is not good, since we need much better resolution than 1Hz.

Where can I see what the update rate is? In MAX?

[Matthew_Williams]

Check page 13 of the manual cFP-SG-140 manual .  Surprised me, too, when I figured it out.

Matt

Message Edited by Matthew Williams on 04-23-2009 03:22 PM

[RTPAX]

I assume you're referring to the table at the bottom, with Filter Setting, Pulse Width, and Pulse Frequency?  I saw that previously while going through the manual, but I interpreted those figures as only applying to the filters that you can apply to each channel, not to the unfiltered channels themselves.  Right now I haven't applied any filters to any of the channels, but you think the pulse frequency column is the update rate for the whole module?

[RTPAX]

Oh, page 13.  I see what you're lookin at. 

Well I'll be.... That is very surprising.  I wonder what we are going to do with our eight SG-140 modules now.  Paperweights? 

You think there might be any way around that update rate?

[RTPAX]

For anyone following along with a vested interest, the answer to my last question is here:

http://digital.ni.com/public.nsf/allkb/BD1530C1F25163BE86256CA9006207DD

Q: "Is it possible to disable the filter or to obtain a faster update rate than those listed in the manuals?"

A:  "No, there is no way to disable the filter.  The fastest update rate is obtained by setting the filter to the highest frequency setting. For the AI-11x, this is 500 Hz; for the SG-140 this is 240Hz. "

[Matthew_Williams]

Hi Ryan.  Sorry to hear the SG-140s aren't going to be a fit for your application.

How old are your modules?  Are they the H revision (H in the part number)?  I have a

customer who uses them on occasion; if you want to sell them I'll ask him if he is interested.

Any chance your requirements can be adjusted to allow the slower update rate?

Matt