Breakpoints with Analog Feedback Hardware: Motion Control>>Controllers>>PCI-7350, Motion Control>>Controllers>>PCI-7340, Motion Control>>Controllers>>PCI-7330
Problem: I have a PCI-735x motion control board and I would like to be able to generate a breakpoint output signal corresponding to my analog feedback. Do NI motion controllers support breakpoints with analog feedback? If they are not supported, what are some other options? Solution: In the NI-Motion User Manual it states the following about breakpoints (in chapter 12, on page 12-2): "The current position is continuously compared against the specified breakpoint position by the encoder circuitry to produce a latency of less than 100 ns." This means that the FPGA circuitry on the motion controller actually uses encoder inputs to determine the breakpoint outputs. Because this is done on the FPGA, it allows the 735x to have the high speed buffered breakpoint functionality. Currently the NI motion controller boards do not support using analog feedback with breakpoints because it is not configured on the FPGA to do this. Also, if analog feedback was to be programmed on the FPGA to work with breakpoints, it would be difficult to determine when an actual breakpoint would be triggered, as there are no rising or falling edges with the analog feedback, just a specific voltage level.One workaround would be to perform some calculations in software to programmatically trigger the breakpoints. The program would constantly poll the ADC voltage and then compare it with a desired voltage level. When the desired voltage is reached, a digital output would be sent out on a trigger line. This method it will most likely not be fast enough for high speed motion and synchronization. Another option that you can consider is to find an analog-to-encoder converter. With the converter, you will be able to get an encoder type of signal which you can use to give you a position feedback similar to normal encoders, thus allowing you to use the breakpoint functionality. Related Links: Support: NI-Motion User Manual NI Developer Zone: 10 Essential Technologies for High-Performance Motion Control NI Developer Zone: Motion Breakpoints used as Triggers for Finite Retriggerable Analog Data Acquisition Attachments:
Report Date: 05/10/2006 Last Updated: 08/16/2007 Document ID: 3X9LH6HB |
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