On 03/07/2015 12:44 AM, Russell Brown wrote: > > Many thanks for all the input chaps. > > The consensus seems to be > > a) Add a mains input filter. > b) Shield the limit switch wires. > c) Stick ferrites in. > d) Mask the problem with a debounce :-)
Another method to consider. Common inputs have high impedance so the full induced voltage from noise gets applied to the input. I have often found that the signal (the good stuff we want) can drive the input to close to 5 Volts, but the input will trip at around 2.5 Volts depending on the input type. So the noise can be weaker than the signal and still be a problem. Placing a resistor from the input to the input's ground can load the noise enough to keep it below 2.5 Volts, but still have the signal above the tripping level. Using signal drivers to utilize 12 or 24 Volt signals I believe is common for commercial machines, and they wouldn't add the cost if it were not needed. Using twisted pair is effective. The twist cancels the induced noise which also can reduce the noise below the trip level, but leave the signal alone. In my experience, shielding and differential drivers haven't been all that effective, but may be worth a try. Beyond a simple load resistor on the input, there are various methods to terminate a cable, such as terminating resistors, matched to the cable impedance, at both ends, to RC filters that can load the noise harder and leave more of the desired signal. I would leave software filtering as a last resort. Adding AC mains filters to VFD's, in my experience, has had the single biggest effect. Also, my HNC lathe had AC filters on the motor leads. When I added a VFD, they turned to smoke and puddles of plastic. The filters were trying to do their job which is to filter high frequency, but the VFD output signal is pure high frequency. I replaced the filters with ferrite beads, but this didn't seem to help much. My HNC lathe has most of the cabling running in common flexible or rigid metal conduit which may help. My mill has no cable shielding, just plain CAT5 twisted pair, input resistors, AC main filters on the VFD, and so far so good. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
