How many FPGA gates should I choose for a Ni 7831R?

[Jingyan]

I notice there are two options about FPGA gates for Ni 7831R : 1M or 3M. But I am really not sure about what is the corresponding memory for these options and how large VIs or algorithms I can download to these FPGA gates.

Basically I want to use Ni 7831R to control a MIMO nano-positioning stage with servo rate above 50kHz. The controller could be pretty complex. The order of controller would be more than 20. We use three AI channels to get feedback signal and three AO channel to send out control commands. I am wondering if !M gates enough for these purpose?

Another question is about software. Do I have to use softMotion Module to develop a controller? Actually at current stage, we don't care too much about trajectory generation. Could We only use FPGA module to develop the controller and generate some simple trajectories (such as circle) offline and send these target position to the FPGA board through FPGA module? Actually I am going to order a Ni 7831R very soon. I need to know if I really need to buy the  softMotion Module or not.

The last thing I am quite interested in is the quality of the AI and AO channels of the Ni 7831R. What is the noise level from the AI and AO channels? I know it has 16-bit resolution. But some I/O channels I used before could give more than 10mv noise, which is much higher than announced resolution.

Thanks
Jingyan Dong

[Jochen]

Jingyan,

this is from our R Series FAQ:

Not all applications require the 3M gate FPGA. Unfortunately, it is difficult to determine whether an application or program will require a 1M or 3M gate FPGA. The following can be used as a general guideline when deciding whether to use a 1M or 3M gate FPGA for your application. For an application that will be performing the timing, triggering and synchronization on the FPGA, a 1M gate FPGA will accommodate the requirements. If the application includes timing, triggering and synchronization along with additional signal processing on the FPGA (control, digital filtering, complex analog triggering), the 3M gate FPGA will give more FPGA fabric to implement these operations

This statement accords also to my own experience so with the facts that you have provided I would go for the 3M FPGA.

The NI SoftMotion Development Module is a great help for designing motion control applications with LV FPGA. There are a lot of shipping examples that can be modified to your needs. I was up and running with my first FPGA based motion control solution and the SoftMotion Development Module in less than 5 hours including all cabling and compiling. Even if you don't use many of your features in your final application this module gives you a jump-start for FPGA based motion control solutions. So yes, I recommend to use the module, but no, it's not absolutely necessary. Of course you can program everything by your own.

Regarding the AI/AO noise and accuracy specifications please refer to the 7831R user manual. In general the noise level is much better than the 10 mV that you have mentioned.

Best regards,

Jochen Klier
National Instruments Germany

Message Edited by Jochen on 08-07-2006 11:03 AM