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Author Topic: brain storm an optimal human safety system for back line  (Read 105196 times)

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #40 on: December 18, 2014, 11:40:25 am »

Exactly.... but my napkin design suggests that a current transformer just might have enough output current to open up a latching reed relay. And a permanent magnet on a push button could "reset" the latching relay if it trips. If that's indeed the case, then this device could fit in a plastic in-line box that connects between the guitar cable and the amplifier. If (and this is a big IF) there's enough current flow from the current sensing transformer to open up the latching relay without amplification, then there are no batteries required. I'm going to see if I can get a few current transformers and latching reed relays to play with.

However, if this was something that could be built and sold for $50 at a profit, would that be too much money? Or is $30 a more acceptable price? Just remember that for this to happen there has to be a certain amount of profit in building and selling it.

What is the impedance of a latching relay winding? Maybe put the relay coil winding right in series with the ground path?

Bzzzt..wrong. I just did a quick search and the lowest current relay I could find at just over 1 mA also required 24V. Elsewhere on the spec sheet they say 30 mW of power to switch the relay and that relay coil is 20k ohm. Relays come in all flavors of coil impedance and working voltage but the bottom line is they need 50-100mW to switch a small signal relay, so a relay with .5V coil requires 140 mA. A big relay would require more power.

=====
My pedal making friend mentioned that some in the guitar industry use transformer isolation for signals, I questioned how well that would work on lead guitar and he didn't answer back.   I expect you use an output transformer in a floor pedal to break the ground path without compromising tone too much. 

JR
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Chris Hindle

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Re: brain storm an optimal human safety system for back line
« Reply #41 on: December 18, 2014, 11:42:27 am »

Just to run out this hypothetical if you have a console grounded mic pointed at the guitar cabinet and the player with guitar in hand touches that mic for any reason he will be putting himself between two EGC systems and exposed to potential shock hazard.

JR
My thinking is that the DI senses >6ma current in the guitar lead, and kills both conductors of that lead.
Exactly what does a humbucker put out, current wise ?? Bob ??
With phantom, or an on-board 9V, I am sure there is plenty of juice available to trip off a reed relay. No power, and the guitar lead is disconnected.
Not all that different from your pedal idea, just move the responsibility to me, not the guitarist. After all, aren't all us sound guys just glorified control freaks ?  :D
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Ya, Whatever. Just throw a '57 on it, and get off my stage.

Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #42 on: December 18, 2014, 01:08:01 pm »


However, if this was something that could be built and sold for $50 at a profit, would that be too much money? Or is $30 a more acceptable price? Just remember that for this to happen there has to be a certain amount of profit in building and selling it.


Unfortunately safety devices don't command the demand that they should IMO.  I find more resistance to safety spending with individuals-with businesses concerned about liability/image etc, usually cost is not a factor. They certainly won't ask the paramedics how much it will cost for an attempt to resuscitate them after they get a good jolt, but "it'll never happen to me" .

So I guess the potential sale price depends on how effective Mike is at educating the masses.  :)
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #43 on: December 18, 2014, 01:44:48 pm »

What is the impedance of a latching relay winding? Maybe put the relay coil winding right in series with the ground path?

Bzzzt..wrong. I just did a quick search and the lowest current relay I could find at just over 1 mA also required 24V. Elsewhere on the spec sheet they say 30 mW of power to switch the relay and that relay coil is 20k ohm. Relays come in all flavors of coil impedance and working voltage but the bottom line is they need 50-100mW to switch a small signal relay, so a relay with .5V coil requires 140 mA. A big relay would require more power.

=====
My pedal making friend mentioned that some in the guitar industry use transformer isolation for signals, I questioned how well that would work on lead guitar and he didn't answer back.   I expect you use an output transformer in a floor pedal to break the ground path without compromising tone too much. 

JR

Drats.... But this would certainly work with an op-amp comparator circuit and a 9-volt battery. However, a failed battery would allow the shock to get through. You could also use phantom for the power, but that's one more connection that can go wrong. More to consider.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #44 on: December 18, 2014, 01:51:09 pm »

Drats.... But this would certainly work with an op-amp comparator circuit and a 9-volt battery. However, a failed battery would allow the shock to get through. You could also use phantom for the power, but that's one more connection that can go wrong. More to consider.

A non-latching relay that opens when power isn't present would be safe, but would draw circa 10mA from 9V battery.

This gets me back to mains power. Since an outlet strip has power... I come full circle back to my smart power strip.

JR 
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #45 on: December 18, 2014, 02:00:26 pm »

Drats.... But this would certainly work with an op-amp comparator circuit and a 9-volt battery. However, a failed battery would allow the shock to get through. You could also use phantom for the power, but that's one more connection that can go wrong. More to consider.

If you want to play along with the design process, here's how these latching reed relays work. http://www.meder.com/fileadmin/meder/pdf/en/Technical_Documents/Application_Notes/ReedSwitchNoOrLowPowerSolution-0209.pdf
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #46 on: December 19, 2014, 03:38:19 pm »

OK more questions for my feature list. If I design my hypothetical "smart" outlet strip, it could combine a conventional GFCI function with a separate relay contact to break the ground connection if it senses current there. ASSuming I could make this smart enough to detect several faults or issues how do we want it to respond. 

On order of increasing severity.

#1 Hot and neutral reversed but good** ground path connection.

Response A- ignore and connect power
   B- indicate the reversed connection but connect power
   C- actively correct the reversed connection before connecting power (more expensive)
   D- do not connect power until reversed connection repaired.

   *** fairly simple to detect floating ground from valid ground, but bootleg ground to neutral will also indicate good unless more testing is added.
   response if ground is floating
      A- apply power to hot and neutral but indicate ground is open
      B- do not power up
      c- internally boot leg ground to neutral and indicate.  (more expensive)

detect for bootleg ground to neutral (more expensive_
   A- if bootleg ground detected light an indicator but apply power.
   B- if bootleg detected do not power up.

detect for RPBG
   A- If RPBG detected light an indicator but still power up (note ground current sense will still shut down the power if any ground current is detected.
   B- automatically reconfigure the correct polarity and bootleg the ground to the actual neutral (with indication that outlet is dangerous)
   C- do not power up.

As you can see many options and I consider some of them too complex and expensive. Alternately manual switches could be used to manually correct reversed polarity and to make bootleg ground connections if needed.  Smart detection could still prevent the main power relay from connecting with faulty power or ground settings.  I could imagine not turning on until a floating ground was manually bootlegged to neutral (IMO safer than floating).

What cha think?

JR
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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #47 on: December 19, 2014, 11:36:02 pm »

Existing GFCIs are designed not to work if hot/neutral are reversed-but they might have to be in the tripped condition for this to work (obviously no one expects an electrician to remove a working GFCI and reverse the wires).

A lot would depend on the reliability of your detection methods-specifically IDing the hot/neutral with a non existent ground.  NCVD are not 100% reliable-and if you bootleg to the wrong wire you create a RPBG-how often is that failure acceptable?  IMO, a floating ground-on a GFCI circuit-is not a big issue for safety, it might be for noise in sound gear.

In a safety class a few years ago, a trainer explained a pet peeve of his-"Wet Floor" signs.  He pointed out you were aware of a hazard-but did nothing to correct it-ie dry the floor, etc.  I may be pessimistic, but I would lean towards letting it feed through power if hot/neutral were correct and ground was either floating or correct any other conditions cause a lock out.
A visual indication of a good ground could be helpful for gear that needs a good ground to run properly.
 
If you have reverse polarity or RPBG, how confident are you that the circuit is otherwise safe to use?

But then I got zapped last spring by an energized green ground wire, so I my tolerance for incorrect wiring practices is at a low point right now! 
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Scott Holtzman

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Re: brain storm an optimal human safety system for back line
« Reply #48 on: December 20, 2014, 01:24:20 am »

Existing GFCIs are designed not to work if hot/neutral are reversed-but they might have to be in the tripped condition for this to work (obviously no one expects an electrician to remove a working GFCI and reverse the wires).

A lot would depend on the reliability of your detection methods-specifically IDing the hot/neutral with a non existent ground.  NCVD are not 100% reliable-and if you bootleg to the wrong wire you create a RPBG-how often is that failure acceptable?  IMO, a floating ground-on a GFCI circuit-is not a big issue for safety, it might be for noise in sound gear.

In a safety class a few years ago, a trainer explained a pet peeve of his-"Wet Floor" signs.  He pointed out you were aware of a hazard-but did nothing to correct it-ie dry the floor, etc.  I may be pessimistic, but I would lean towards letting it feed through power if hot/neutral were correct and ground was either floating or correct any other conditions cause a lock out.
A visual indication of a good ground could be helpful for gear that needs a good ground to run properly.
 
If you have reverse polarity or RPBG, how confident are you that the circuit is otherwise safe to use?

But then I got zapped last spring by an energized green ground wire, so I my tolerance for incorrect wiring practices is at a low point right now!

I may be off base but let me toss something out.  Rather than analog devices have you consider a small uP?  Certainly if a small RF tracer signal ,from an amplified TTL output switched on and off very fast, was induced on the hot leg the corresponding return signal would radically differ with a device that produced a hot chassis.  By producing a couple 100 samples of gear in distress the samples could be plotted and a distress signature identified.

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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #49 on: December 20, 2014, 08:40:38 am »

Existing GFCIs are designed not to work if hot/neutral are reversed-but they might have to be in the tripped condition for this to work (obviously no one expects an electrician to remove a working GFCI and reverse the wires).

I'm not sure that's true. If the GFCI doesn't require a ground wire, then just how does it tell the difference between correctly wired and swapped H-N connections? The big question should be does the GFCI open up both the Neutral and Hot lines? I believe they do, at least in the ones that I've seen. But perhaps there are versions that only open up the "Hot" side. If that's the case, the a tripping GFCI would not isolate you from a ground fault shock.
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Mike Sokol
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Re: brain storm an optimal human safety system for back line
« Reply #49 on: December 20, 2014, 08:40:38 am »


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