CompactRio 1M chassis or 3M chassis?

[Sean Dougherty]

I am trying to decide if I need the 1M gate chassis or the 3M gate chassis for my application. I think the 1M will suffice but I wanted to make sure. I'm planning on reading two quadrature encoders, determining there speed, and logging that data. The pulse train on the encoders could be at a pretty high frequency but I don't know the value yet. I'm also measuring 4 analog inputs 4 temperature sensors and outputting two analog outputs at lower rates. Will a 1M gate chassis suffice for this application?

I may eventually also want to do closed loop, PID control of two motors, reading their encoders then outputting an analog voltage to adjust the speed. Is this possible with the 1M gate chassis? Is the rate at which I can execute the PID loop affected by the number of gates or does this just represent the number of operations I can do (and if so, is this enough to do all the operations I want). Most of what I will be doing will be simply logging the data but doing PID control will require more operations obviously.

Thank you for the help. I plan to purchase the CompactRio hardware as soon as I get an answer to these questions.

Sean Dougherty

[Ashish Uttarwar]

Hi Sean Dougherty,

I am not sure of your application requirements but one of my projects involved two quadrature encoders and a DC motor. Only difference was the I used NI PCI 7831R FPGA Board and not cRIO. My RT was running on a desktop PC.

If you check http://www.ni.com/pdf/products/us/04_3632_301_101.pdf; page 3; they mention that the PCI 7831R FPGA board has 1M gates. My project involved balancing a pendulum in inverted position.

1M gate FPGA board worked perfectly fine for me ( 2 encoders and DC motor). I am not sure about the performance of the 1M gate FPGA for your application, since it involves more data acquisition. But, it should work fine for 2 encoders and motor. NI has PID controller for FPGA and hence you can use the FPGA to fullest capacity.

Still, I am not sure of cRIO performance compared to a desktop PC and if that really matters in regards to FPGA performance.

Let me know if this information helped you. All the best.

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Ashish Uttarwar
James Kring, Inc.
www.jameskring.com