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Author Topic: brain storm an optimal human safety system for back line  (Read 100563 times)

Bob Leonard

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Re: brain storm an optimal human safety system for back line
« Reply #110 on: January 04, 2015, 08:21:17 am »

The two (2) words guitar players need to see are "Improves tone". So the model number for my safety device will be  - BLIT-FCB, or BLIT-MCB. Care to guess?
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BOSTON STRONG........
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #111 on: January 04, 2015, 10:46:56 am »

The two (2) words guitar players need to see are "Improves tone". So the model number for my safety device will be  - BLIT-FCB, or BLIT-MCB. Care to guess?

"Bob Leonard's Improved Tone- Female and Male Capacitor bypass"???  Close?

My only design goal is to "maintain" original tone, not improve it, while I guess the line cord phools may expect audible effects from messing with power ground connections.

JR
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #112 on: January 04, 2015, 10:54:23 am »

The two (2) words guitar players need to see are "Improves tone". So the model number for my safety device will be  - BLIT-FCB, or BLIT-MCB. Care to guess?

IDK...  ;D
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #113 on: January 10, 2015, 03:11:45 pm »

I am still thinking about this and have distilled it down to a hot chassis microprocessor and a 3 pole relay.

When the outlet is powered up the microprocessor A/D inputs perform a NCVT measurement on the floating output side neutral and ground wrt the input side neutral. The micro inputs are high enough impedance that I should be able to tell the difference between a correct and reverse polarity power source. If it senses hot where neutral is supposed to be, it never turns on and the relay stays disconnected.

If it detects good power polarity the relay closes and applies power the GFCI protected outlets. Then the A/D convertor measures voltage drop across a modest resistance in series with the ground. This R can be much smaller impedance than a stinger cap since the relay will open up pretty quickly if it senses mA of ground path current.

I am not looking forward to breadboarding and debugging  a hot chassis design but that is the practical way to do this... a couple dollar micro, a PCB and some glue circuitry. The relay and GFCI outlets will be the most expensive parts, and not that bad for production(?).

About the only way this could be fooled is reversed mains power "and" hot ground on the outlet side, but I should be able to even catch that by NCVT probing the outlet side neutral.

So the plan is coming together... I still don't feel warm and fuzzy about this ever being a commercial product. And If the safe outlet strip refuses to power up, will the musicians just plug in around it (the show must go on)? Maybe I could build in a siren or crowbar clamp across the mains to take out the circuit breaker every time it detects reverse polarity power. :-) While that is electo-passive aggressive. RP is only dangerous in combination with BG.

JR

PS: Of course this is still conjecture until I build one and confirm that I can reliably make NCVT determinations with a cheap micro and outlet strip wiring. It will be easier to pick up an ambient ground with actual products plugged in.   
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Robert Lofgren

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Re: brain storm an optimal human safety system for back line
« Reply #114 on: January 10, 2015, 07:59:41 pm »

I am still thinking about this and have distilled it down to a hot chassis microprocessor and a 3 pole relay.

When the outlet is powered up the microprocessor A/D inputs perform a NCVT measurement on the floating output side neutral and ground wrt the input side neutral. The micro inputs are high enough impedance that I should be able to tell the difference between a correct and reverse polarity power source. If it senses hot where neutral is supposed to be, it never turns on and the relay stays disconnected.

If it detects good power polarity the relay closes and applies power the GFCI protected outlets. Then the A/D convertor measures voltage drop across a modest resistance in series with the ground. This R can be much smaller impedance than a stinger cap since the relay will open up pretty quickly if it senses mA of ground path current.

I am not looking forward to breadboarding and debugging  a hot chassis design but that is the practical way to do this... a couple dollar micro, a PCB and some glue circuitry. The relay and GFCI outlets will be the most expensive parts, and not that bad for production(?).

About the only way this could be fooled is reversed mains power "and" hot ground on the outlet side, but I should be able to even catch that by NCVT probing the outlet side neutral.

So the plan is coming together... I still don't feel warm and fuzzy about this ever being a commercial product. And If the safe outlet strip refuses to power up, will the musicians just plug in around it (the show must go on)? Maybe I could build in a siren or crowbar clamp across the mains to take out the circuit breaker every time it detects reverse polarity power. :-) While that is electo-passive aggressive. RP is only dangerous in combination with BG.

JR

PS: Of course this is still conjecture until I build one and confirm that I can reliably make NCVT determinations with a cheap micro and outlet strip wiring. It will be easier to pick up an ambient ground with actual products plugged in.
This sounds like the detection I suggested early in this thread by using an antenna and opamps to detect if 50/60hz is present on a single wire.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #115 on: January 10, 2015, 08:38:04 pm »

This sounds like the detection I suggested early in this thread by using an antenna and opamps to detect if 50/60hz is present on a single wire.
That is kind of the principle of all NCVT but it isn't about op amps for voltage gain, but high enough input impedance to not load down electrostatic coupled environmental voltages. While a NCVT may have one real conductive lead, the weak coupled ground reference is coming from the device chassis-handle via very high impedance.
   
I am not adding voltage gain and don't care about the Hz. The microprocessor A/D inputs are pretty high impedance and decent resolution (3V/ 12bit). I will start out ASSuming that the mains wiring is correct polarity and ground the micro to neutral. I will cap couple into the A/D inputs and sniff for significant voltage. If the A/D is grounded to real neutral (0v) and I sniff other lines that should be close to 0V I should only get insignificant input voltage readings. OTOH if the outlet is reversed polarity the effective ground that the micro is using for comparison is now swinging 120V AC, when I then sniff some floating 0V lines like he not yet powered up outlet neutral, the weak 0V compared to the micro swinging 120V will now register as a measurable voltage (I hope).

If I sniff and all is good then I will connect power and use two of the A/D inputs to measure current flowing in the ground through a resistor. For this to work well ground  and neutral need to be within 3V of each other, but I can deal with them being even further apart if needed, since I measure both ends of the resistor and just subtract one end from the other.

The unknown to me is the sensitivity of the microprocessor A/D inputs. I need to cap couple through small enough capacitors that the current from them hitting the input clamps with full mains voltage doesn't melt silicon, while large enough to get useful readings (especially for the current sensing which will be mV not 100V).

I believe this will work.

JR
 
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Don Boomer

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Re: brain storm an optimal human safety system for back line
« Reply #116 on: January 12, 2015, 01:29:17 pm »


So the plan is coming together... I still don't feel warm and fuzzy about this ever being a commercial product.

Not telling you anything you don't already know ... but how many $$$ would need to be added final cost to offset your liability for such a product? 

That said, I'd be happy to be a  beta tester.  8)
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #117 on: January 12, 2015, 01:54:27 pm »

Not telling you anything you don't already know ... but how many $$$ would need to be added final cost to offset your liability for such a product? 

That said, I'd be happy to be a  beta tester.  8)

Yes. there is a certain irony in liability exposure from trying to protect musicians from bad wiring. The good news is I do not see a chance in hell that this could ever be commercially successful (it's hard enough dragging drummers into the 21st century).

[edit]
Upon reflection the addition of a cut off relay and GFCI outlet into an outlet strip does not seem all that dangerous, the failure mode (relay did not open) would act just like a normal outlet strip, with GFCI. Of course any commercial product would need to be vetted by UL.

Customers still need to avoid dangerous situations even with extra protection devices in use.
[/edit]

If I reduce this to a working design (it still needs to be proved on the bench and code written) I will publish the details and share it for others to use.

This is academic if all mains wiring was properly done and vetted.

JR
« Last Edit: January 13, 2015, 12:41:42 pm by John Roberts {JR} »
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Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #118 on: January 16, 2015, 12:48:44 pm »

This is academic if all mains wiring was properly done and vetted.

Until something changes... either an intentional modification to the electrical system (authorized or unauthorized) or damage such as water intrusion or corrosion, other physical abuse and damage, normal wear, or connecting faulty equipment that doesn't quite trip the OCPD/GFCI.

Point being, any vetting or certification is only valid for the date and time the examination happened. As time progresses, the risk increases, so the need for additional safety gear becomes more important.
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Stop confusing the issue with facts and logic!

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #119 on: January 19, 2015, 11:44:29 am »

Good news- bad news. Good news I am coming up with a workable plan for my smart outlet.

#1 test for floating ground.  (do not close relay?)
#2 test for reverse polarity   (do not close relay?)
#3 test for bootleg connection  (do not close relay?)
#4 test for current flowing in ground (open relay).

The bad news is coding the microprocessor brain involves running the processor in an emulator connected to a computer. I am very apprehensive about connecting my computer to a hot chassis design. Especially one capable of being connected to RPBG to detect the faulty wiring. 

I may have to rig up a floating transformer isolated prototype but this still seems a little dicey. I just researched buying a formal opto-isolated emulator rig from the microprocessor company I use and they want over $400  :( . A generic JTAG opto interface is probably $50 but then I would have to discover all the secret handshakes to get it working.

arghhh...

JR
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