I build and service machines that include unfortunate noise sources (arcing relays and highly inductive motors) as well as a variety of low voltage electronics. Several of my co-workers and I have been mystified as to why what seems like very heavy duty grounding along with careful adherence to star grounding methods does so little to protect our low voltage circuits from noise related problems, like glitches on a character display every time a motor starts.
I think I may finally be starting to understand at least one of the issues in play here, but wanted to stop by for a sanity check.
We thought our grounding should be solid because it seems to go to all the right places, following all the right paths, and with very, very low resistance. But it occurred to me recently that impedance is a function of frequency and that our noise bursts include high frequencies (behind my ability to accurately measure with my beat up oscilloscope, but appears to be at least 1MHz.)
Is it possible that, although our grounding is already severe overkill for DC returns and for safety concerns regarding 60Hz AC, it presents a much higher impedance to this high frequency noise?
If so, where do I start in trying to improve things? We've got #8 copper wire connecting the frame ground to the building ground, #12 copper wire bonding the only two frame components that could otherwise become electrically isolated from one another, and less than 8" of #16 copper connecting the DC common for our low voltage board to the star grounding point. The frame itself is maybe 3' x 2' x 1' and fabricated from stainless steel, most of it nearly 1/8"thick. All of these components show incredibly low resistance with an ohm meter, but I only recently thought of the varying impedance for different noise frequencies.
I think I may finally be starting to understand at least one of the issues in play here, but wanted to stop by for a sanity check.
We thought our grounding should be solid because it seems to go to all the right places, following all the right paths, and with very, very low resistance. But it occurred to me recently that impedance is a function of frequency and that our noise bursts include high frequencies (behind my ability to accurately measure with my beat up oscilloscope, but appears to be at least 1MHz.)
Is it possible that, although our grounding is already severe overkill for DC returns and for safety concerns regarding 60Hz AC, it presents a much higher impedance to this high frequency noise?
If so, where do I start in trying to improve things? We've got #8 copper wire connecting the frame ground to the building ground, #12 copper wire bonding the only two frame components that could otherwise become electrically isolated from one another, and less than 8" of #16 copper connecting the DC common for our low voltage board to the star grounding point. The frame itself is maybe 3' x 2' x 1' and fabricated from stainless steel, most of it nearly 1/8"thick. All of these components show incredibly low resistance with an ohm meter, but I only recently thought of the varying impedance for different noise frequencies.