How the chattering of relay causes noise ? Is it its on-off sound makes the noise? I want to know how to couple a relay chattering noise to a data cable.
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2\$\begingroup\$ By "noise" I assume you mean electrical noise? If so, it's because of two main reasons, one is that the relay has a (relatively) big coil of wire and when it's powered up then powered down it produces a changing magnetic field (which can couple noise into anything conductive, but it's usually a weak close-proximity effect). The more likely reason is because when the relay opens, there's a little spark (assuming the contacts were carrying power at the time) and sparks are very good at generating and broadcasting all manner of electrical noise, your cable is acting as an antenna for the noise. \$\endgroup\$– SamCommented Jan 24, 2017 at 6:02
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\$\begingroup\$ Could you elucidate on this "data cable" please? There are a lot of data cables out there, and some are much easier to induce noise on than others. \$\endgroup\$– uint128_tCommented Jan 24, 2017 at 6:09
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\$\begingroup\$ @Sam Yah I mean the electrical noise. So piratically how can I couple the noise because of chattering of relay with a cable carrying data? \$\endgroup\$– Nikhil NCommented Jan 24, 2017 at 8:27
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\$\begingroup\$ My guess is: remove the shield of the data cable (if it has one), wrap the wires multiple times around the relay and pass a meaningful current through the relay contacts while switching the relay on and off. \$\endgroup\$– SamCommented Jan 24, 2017 at 20:22
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\$\begingroup\$ Years before microprocessors (way back) we use to do this to generate electrical radiated noise for testing. It was crude and rude but it worked. Getting it close to the circuit (maybe a foot) it could cause lots of symptoms in the circuit). The bigger the relay the greater the electrical noise. We did not run it long as the relays would eventually fail. \$\endgroup\$– GilCommented Aug 7, 2022 at 20:29
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1 Answer
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Usually when people talk about chattering in a relay, they mean in the sense of electrical noise rather than audible noise. When a relay closes, ideally it's a single, instantaneous switching action. In reality, the relay will 'chatter' when the circuit closes because of contact bounce, worn contacts, etc. There will also be noise when breaking the circuit because of sparking between contacts. Here's a video from Dave of the EEV blog describing contact chattering and the methods for overcoming it from a signals processing standpoint. https://www.youtube.com/watch?v=Nj-Q8FQxHhU
For a relay's typical use, as a rarely-switched power device, relay chattering is usually inconsequential. For example, the (resistive) broil element of an oven does not care if there's a millisecond of electrical noise when the relay is switched.
However, a data line should not have spurious noise. In addition, relays are not meant to be rapidly switched! The contact is usually driven by an inductive coil (which resists rapid switching) and the contacts are worn down by the switching action. If you want to drive a data line, use a transistor instead.
