Specific EMI/RFI interference problem

[gar]

071019-2040 EST USA

glentner:

It is very likely that your spindle motor is a major source of your problem. The question is thru what major path(s) is the noise getting into your system. It is quite likely that it is the parallel port.

Is your limit switch really required to run the program? If it is not, then you can put a short jumper wire, 1" max, at the parallel port connector in place of the limit switch. You just have to be ready to stop the machine manually if it is headed to the limit.

If there is no failure with this test, then we can assume that most noise enters the system thru this input connection. Next connect either existing wire or both that go to the limit switch to the input short. Again test for malfunction.

If no failure, then put a 0.1 mfd ceramic capacitor at the input in place of the short, and a 1 K resistor to the signal input terminal. Connect the free end of the resistor to signal common, any pin from 18 thru 25. Will the program run? If it does not, then is there a malfunction which may be the resistor is too large. In this case change to a lower resistance, but the largest that will work. If function is OK, then remove free end of resistor and connect to one wire to the limit switch and the other limit swtich wire to signal common. Now do we get a failure? If no failure, then that is good, but it is not the end of testing because you really want to know what your margins are.

071020-0552 corrected last paragraph which previously made no sense.

.