Hardware for Synchronous Analog and Digital Measurement

[Maxmai98]

Good evening everyone,

I am currently working on a project for my thesis, in which we need to dynamically evaluate a positioning sensor. For this, we are using two Piezo actuators with included SG analog sensors. The signal of the two analog sensors will then be added (superposition) and compared with the digital positioning sensor. Therefore, the synchronicity of all three sensor is of vital importance.

To achieve the synchronicity between the analog sensors, I think the Voltage input module NI-9215 should be appropriate, due to the 16-Bit resolution and simultaneous sampling of different channels. With this module, we can sample both analog signals at the same time or at least get a Synchronization through a trigger. I found more information about this under the following link: https://www.ni.com/en-us/support/documentation/supplemental/21/synchronizing-analog-input-c-series-m...

For the Digital signal is where I don’t really know what to do. I think there is a way to do a similar triggering directly through software: https://www.ni.com/en-us/support/documentation/supplemental/06/timing-and-synchronization-features-o...

I also read, that it would be possible to directly wire the digital signal to the AI Module and thus acquire the data simultaneously. https://forums.ni.com/t5/LabVIEW/Digital-and-analog-in-at-the-same-time/td-p/76364

I would then use the cDAQ-9174 as the chassis. Nevertheless, there is also an ethernet chassis (cDAQ-9185) with Synchronization Enabled and Onboard triggering. I am unsure if these options are necessary to achieve what I explained above. If theses options are not necessary, I would use the USB option, since (from what I can tell) it has a smaller latency.

Any suggestion would be highly appreciated.

-Max

[Kevin_Price]

You should also be using a digital input module compatible with your positioning sensor.  Is it a quadrature incremental encoder?  Are the signals differential or single-ended?  The answer to the latter question will be important in choosing an appropriate cDAQ digital module.

After that, the summary is: you'll be fine.  This is very do-able.  The first article demonstrates a couple possible methods -- Start Trigger Synchronization, and Sample Clock Synchronization (my personal go-to).  It illustrates things using NXG, the now-discontinued product that decided (among other things) that making LabVIEW code look more like a Fisher-Price toy was another great idea in rebranding.  Nonetheless, regular LabVIEW has all the same functions to do the same thing, just without the gently rounded corners and graphical Nerf coating.

The second article is also full of good info, including a lot more than you need at the moment.  So don't worry if you're a little lost in all the info.

The third link is to a *very* old forum discussion that was once relevant, but has been obsolete for a very long time due to a subsequent major overhaul of the DAQ driver and several newer generations of DAQ hardware devices.  Ignore the warnings about limitations there, most of them don't apply any more.

I'm not a cDAQ expert, but I strongly suspect that the 9174 chassis will be sufficient.  Latency shouldn't matter much unless you intend to run an active control loop.  If you're just collecting data to be post-processed it won't affect you.

-Kevin P

[Maxmai98]

Hello Kevin,

thank you for your extensive explanation, it was extremely helpful!

I managed to get my hand on a NI USB-6343, which should be even better than the voltage measurement card from NI. I have been told, that the Digital sensor can also be read through CAN-Bus. I would use this Bussystem for the digital communication.

I will still keep your advices and explantations in mind.

Thanks again

Max