Noise, Interference, and unexplained electrical behaviour

[Neale]

Is that more sophisticated decoupling/filtering on the power lines, or is there also something on the signal lines to try to keep noise out? I would guess that it's power only due to effects on pulse shaping, etc, but curious to know. Does it also imply that with lower-spec drivers, it might be worth adding some filtering on the power lines at the driver terminals (or even just inside the box for those brave enough)?

[g4ghp]

Is that more sophisticated decoupling/filtering on the power lines, or is there also something on the signal lines to try to keep noise out? I would guess that it's power only due to effects on pulse shaping, etc, but curious to know. Does it also imply that with lower-spec drivers, it might be worth adding some filtering on the power lines at the driver terminals (or even just inside the box for those brave enough)?

Hi Neal, the coupling was actually on the main pcb, and it would be quite difficult to modify an existing pcb as space, and track layout would be a nightmare. But you have hit the nail on the head with regard to the power supplies and both the signalling and supply lines. more robust measures can be taken and often improve a poor situation.

Take for example the standard linear psu that many people build, using a toroidal transformer, bridge rectifier and electrolytic capacitor. Standard toroidal transformers are very susceptible to external interference of varying type and magnitude. They easily become one of the prime sources of spreading interference within a cabinet set up......typical of many of the cnc installations. So, how do you resolve this problem?. First have the mains introduced to the power supply chassis via a fully grounded and screened mains socket/ input filter, providing enough attenuation to interfering mains spikes. Secondly the toroidal transformer spec. For example the psu I put together recently required a 2x25volt secondary to give me approximately 70 volts. pay a bit more money and get a toroidal that has both a electrostatic screen, and a emi/rfi shield, so then you know the transformer is not going to be susceptible to any external interference. Next, put the whole thing (psu) in an aluminium box (rf tight) and take the output from the psu via a substantial feed through capacitor, capable of handling the maximum current and a bit more. Then for final measure, wrap the output lead through a emi ferrite ring to kill off any other external noise of rf influences.

So there you go, it all makes sense, and is easily achievable but it does cost a bit more, and there is a bit of chassis bashing to be done , but you now know that if you are having problems of interference or noise, your main psu is unlikely to be responsible.