Questionable ESD Practices

Snake In The Tube

The following has been proposed as a method of ameliorating ESD (Electro-Static Discharge) damage to the volume side electronics:

Instead of simply connecting the volume antenna to the electronics (top left), an insulated wire is snaked through the tube (middle left).  The wire has an insulating plastic jacket that is rated at some high maximum voltage, say 1kV.  At first glance this would seem to strongly imply that we are insulating the volume electronics with 1kV of ESD protection, but that's probably not the case.

The wire in the tube forms a concentric cylindrical capacitor, for which there is a closed form solution (right).  Assigning reasonable numbers: length = 1m, wire radius = 1.5mm, tube inner radius = 4mm, which yields a calculated capacitance of 57pF.  The exact value isn't all that important, we're just looking for a ball park number to have some idea of what we're dealing with.

So, for theoretical purposes, we can replace the wire with an explicit ~57pF bulk capacitor (bottom left), also with a rating of 1kV.  Has anything changed in terms of ESD?  To know for sure you would have to test both cases to failure!  But lets talk about what ESD does.  In the worst case it is an abrupt electrical discharge of hundreds or thousands of volts.  The abruptness means it has a lot of high frequency content (events that are small in the time domain are large in the frequency domain, and vice-versa).  The conduction through a capacitor is proportional to frequency, so the capacitor could easily look more or less like a dead short for ESD edges.

My feeling is that there probably isn't much difference between the distributed wire capacitor and the explicit bulk capacitor, and a series capacitor probably isn't all that effective at limiting ESD damage in the first place.  It might be better than nothing but to know for sure you would have to test both cases to failure!

It's also my feeling that insulating the outer surface of the tube itself is probably more effective at dissipating ESD before it reaches the tube, but to know for sure you would have to test both cases to failure!

You will notice on my D-Lev thread that I make absolutely no mention of how effective (or ineffective) the ESD protection implemented on the AFE is because to know for sure I would have to test to failure and I haven't done that.  Making sweeping claims as to the effectiveness of a particular implementation of a particular ESD protection scheme without doing actual testing is foolhardy in the extreme.

dewster,

Something has happened, it is nice to see you share interesting stuff again. I feed HV wire of 40kv in my tube, static is around 11kv. The length I feed determines the sensitivity of my volume loop. In basic electronics this is a capacitive interaction which is why there is protection. When the static spark hits the volume loop the voltage is dissipated through the entire mass and is so weak it will barely rise, basic capacitor fundamentals. When you have a direct connection into your circuits, a major engineering flaw of course something has to give like when it bites your finger. This is why I think it is done on purpose for sales.

Christopher
www.Hwy79.com

"I feed HV wire of 40kv in my tube, static is around 11kv."  - oldtemecula

One can purchase HV bulk capacitors.

"In basic electronics this is a capacitive interaction which is why there is protection."

A capacitor can protect against DC, but ESD is largely a transient / AC thing, and in that situation they conduct.  You would have to explain your thinking here because I don't see it.

"When the static spark hits the volume loop the voltage is dissipated through the entire mass and is so weak it will barely rise, basic capacitor fundamentals."

A larger capacitance can store more energy with a smaller voltage differential, but the capacitance arises from both plate area and electrolyte composition.  So a bulk capacitor should theoretically behave the same as a wire in a tube, and one side of the plate is instantly and fully charged in either case.  So I'm not getting your thinking here either.

If anything, I imagine insulating the outside of the volume tube would yield better protection, as then the hand is one plate of a capacitor and the tube the other.  This would physically limit the interacting plate area and electrolyte volume of that capacitor, and thus limit the energy transferred / slow down the transfer.

"When you have a direct connection into your circuits, a major engineering flaw of course something has to give like when it bites your finger. This is why I think it is done on purpose for sales."

My feeling is it's: hope as a plan, lack of imagination, and lack of not testing to failure.  What testing have you done?

I wish I could test this, I had a taser flashlight but they seem to prevent me getting the batteries out of it.

What would you use?

The metal loop bleeds the static charge off to the atmosphere, your big capacitor way is going to mess up the capacitive proximity effect.

Do you think the capacitive loop model to the player is accurate? I think it is cute but flawed.

dewster says: Static is not all DC? You got to give me a reference for that thinking.

Christopher

"I wish I could test this, I had a taser flashlight but they seem to prevent me getting the batteries out of it.  What would you use?"  - oldtemecula

So you haven't tested this then.

"The metal loop bleeds the static charge off to the atmosphere, your big capacitor way is going to mess up the capacitive proximity effect."

I don't understand what you mean by "capacitive proximity effect."  When it comes to metal, electrons are free to move.  The electrons on one plate of a small bulk capacitor connected to a metal plate will "see" the plate and pipe as one thing.

"Static is not all DC? You got to give me a reference for that thinking."

Static discharge = ESD event = AC.

Resonant Shunt

The following has been proposed as a method of ameliorating ESD (Electro-Static Discharge) damage to the pitch side electronics:

A high Q coil is placed between antenna and ground.  Presumably this inductance is substantially higher than the LC tank inductance, so that it's inductive reactance is minimal at the operating frequency.  Except for DCR (the Direct Current Resistance of the coil winding) this is a dead short for DC currents, so at first glance it perhaps seems ideal for conducting away ESD events, but that's probably not the case.

ESD events are usually quick discharges, and when a resonant circuit is subjected to an impulse it will ring, with a decay rate based on total Q, as well as non-linearities and other loads the coil "sees".  The antenna and oscillator present capacitance, and when a coil and capacitor are coupled you get resonance, as the coil and capacitor are inverses of each other in terms of energy storage.  They shuttle energy back and forth between them, ringing until the energy is fully dissipated via heat (resistively) and/or RF (radiation).

So an ESD event hits the antenna and the L goes from zero (ground) to some high voltage.  This is because inductors look like very impedances to very high frequency signals such as fast edges, so even though one side of the inductor is grounded and it has DCR and such, the other end is flapping in the wind when it comes to fast tugs, which takes us from 0 to point A (right).  The inductor "sees" the voltage across it and starts to conduct, taking the antenna back to zero volts at point B.  Great!  ESD is squashed!  No, the inductor can't stop on a dime and so overshoots through zero and takes us to point C in the negative direction.  Oh no!  We've taken a high input voltage and almost doubled it!  And so on to points D, E, etc. with a single ESD event now turned into multiple high voltage events.

But wait, maybe there's something going on inside the oscillator that damps all this or something?  Maybe, maybe not, it all depends.  I think this ESD method is potentially more dangerous than the "Snake in the Pipe" as it has the obvious ability to increase the damage to the oscillator due to an ESD hit.  But, as usual, to know for sure you would have to test both cases to failure, the case with the inductor and the case without.

dewster, you are showing me a lot of affection lately. I am not going away immediately so relax.

I can do this test, what source can I use for the discharge of 10kv that you will accept?

My osc transistors are rated at 300 volt MPSA42-AP which is for the sound I get but that also helps.

I will have the spring coil connected to the 4 ohm 3300 uh choke.

Discharge into the spring and watch the amplitude on the scope 10:1 at the top of the earth grounded choke.

Will find a way to make a video of the discharge and scope trace.

Now I am doing dewsters homework as there is nothing to prove to me but he is curious.

Christopher

"I can do this test, what source can I use for the discharge of 10kv that you will accept?"  - oldtemecula

It's not me you need to convince that your ESD protection is indeed effective, it's you.  Preferably before you make any claims regarding it, but that horse has already left the barn.

"Now I am doing dewsters homework as there is nothing to prove to me but he is curious."

I honestly have almost zero interest in this, but I thought you owed it to yourself and others to do the due diligence thing after repeatedly making unfounded and untested claims.

This looks ideal for this experiment  20kv for $10  BBQ igniter. dewster will complain no matter how I set up the experiment but I am curious.

"This looks ideal for this experiment  20kv for $10  BBQ igniter."  - oldtemecula

Before you blow it up do a linearity video.