DAQ input with PXI and digital output fater than 47uSec

[Marco Amorim]

Hi there,

Folks, I have to create a demo for a proof of concept evolving PXI and DAQ...
This aquisition demo is asked by a motor company and they want to know it is possible to be done with PXI.

The scenario --> we must follow AC-sinusoidal signal from power line (outlet for an instance) and make a zero-cross detection.
Once we have a zero-cross detection, a digital output line must be set high and kept high for no less than 80ms. After this, it can be set low either manually or automatically.
The proof of concept relies on assuring the digital line is set high faster than 47 uSeconds with all assumptions above

It it possible? Does LV RT support that?

HW:
PXI-8176
PXI-6115


All seugges
tions are welcome,

[Christian_L]

Marquinho,

This type of application could very well be handled using the LabVIEW FPGA Pioneer System (http://sine.ni.com/apps/we/nioc.vp?cid=11834〈=US). The FPGA Pioneer System allows you to download LabVIEW code to the FPGA on the Reconfigurable I/O hardware. The code running on the FPGA will provide you suitable performance and determinism to generate the signals you need. The reconfigurable I/O hardware provides 8 AI, 8 AO and 96 DIO lines and can handle a number of DAQ tasks at the same time. This solution can be integrated with LabVIEW or LabVIEW Real-Time.

Christian L
NI Consulting Services

[thayles]

There is a way you can do this with your 6115 and DAQmx.

1. Configure an analog input task. You can make it finite so you're not continually acquiring uneeded data. This technique will work until you stop or clear the task.
2. Configure an analog Start trigger to look at this signal and trigger at the zero crossing. Use PFI 0 as the source of the analog trigger.
3. Configure a counter to produce a single, retriggerable digital pulse of 80mSecs. There is an example program that already does this. Set the low time to a small number (like 100 nSecs).
4. Configure this counter to use a digital rising edge Start trigger and select the AnalogComparisonEvent as the source.
5. Start both tasks.

Now, everytime the analog signal crosses zero, the AnalogComparisonEvent (the output of the trigger circuit) will go high and will trigger the counter to produce its pulse. It's all done in hardware.

The attached VI does run the analog input task continually but only so that it can plot the waveforms.

- thayles