ask council to buy systems adapted to acquisition and treatment real time

[gregt]

Hi,

My team wishes to buy systems allowing to make acquisition real time of 8 signals and to treat them in a dll in order to return an output signal at a system.
The frequency of execution of the loop must be equal to 30 kHz or better.

Thus we need several councils of experts to choose the good systems.
We need also to know if the programming with labview CVI and labview Real Time is the best type of programming to obtain the most powerful possible applications.

Thanks in advance.

[aasenjo]

Greg,

The desired rates are quite high, given the number of channels. I would suggest considering the following options:

- Distributing the control loops among several PXI-8176/8186 controllers

- Using FPGA to perform the signal processing in hardware, therefore allowing very high loop rates.

The first option is probably going to force you to use 8 PXI controllers, one for each signal, assuming the signals can be treated independently. Current PID loop rates for 2 channels (on a PXI-8186) are at around 27 kHz (below what you want), and one channel rates are at about 42 kHz (for a PXI-8186)

FPGA is truly the best option for your application, so please make sure you look into it. The only caveat is that the FPGA code would not allow you to use a dll fo
r signal processing. You would have to implement the signal processing in LabVIEW, it would then get converted to hardware on the FPGA, allowing much higher rates than possible with any software-based approach.

At least this should get the ball rolling. Other developers might want to comment on their experience.

I hope this helps,

Alejandro Asenjo
LabVIEW RT R&D
National Instruments

[gregt]

Thanks much for your answer, Alejandro

With your council we start to have a good idea of the systems which we must use.
We are interested by the PXI 8186-RT controller and the DAQ card PXI-6071E.

However, we also wish to know how many PXI controller we should use if we decrease the rates: loop rates equal to 10kHz (for the 8 signals) and if we do not make treatment "point by point" but with buffer(s) (but the acquisition will be always uninterrupted, continuous).
This is important to confirm our choice.

Regards,

Greg

[srm@viewpointusa.com]

you should only consider the point by point if your output signal requires an update at the same rate. two controllers if you decrease your rate to 10kHz. This will only be acheivable with careful design. What is the algorithm for the output? If it is time consuming, you will not achive your rate, if you do nearly anything else at the same time, you will not achieve the highest rates.