ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 ... 17 18 [19] 20 21 ... 55   Go Down

Author Topic: brain storm an optimal human safety system for back line  (Read 105668 times)

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16416
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #180 on: March 08, 2015, 02:35:13 pm »

Yesterday I bought a cheap neon lamp tester at Wally World for $2.95... Works like I remember and it is UL/CSA approved (category 2, 300v max).  When connected across 120VAC it draws 250uA which is consistent with 100k series resistance and 95V lamp breakdown voltage.

Testing my loose neon lamps that just showed up the same measurement indicates 500uA so more like 70V lamp breakdown.

I can light the neon lamps one at time by touching the free lead (just like the tester), but when the lamps are connected together they work differently than I thought.   Two neon lamps in series with 120V across the pair do not light at all, that is not unexpected but what was, if I grab the junction of the two lamps, both light up??? If I add diodes neither one lights up (the rectified AC probably charges my body capacitor up to 150V DC just like static charges do).

Interesting I only measure 2 uA of current from me grabbing the neon lamp with my hand so hard to see in direct light.

Based on this preliminary testing I still like the $3 neon lamp tester to parse out hot leads in an outlet, but I could already do that with my VOM.

MO later...

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

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2258
Re: brain storm an optimal human safety system for back line
« Reply #181 on: March 08, 2015, 05:25:13 pm »


I can light the neon lamps one at time by touching the free lead (just like the tester), but when the lamps are connected together they work differently than I thought.   Two neon lamps in series with 120V across the pair do not light at all, that is not unexpected but what was, if I grab the junction of the two lamps, both light up??? If I add diodes neither one lights up (the rectified AC probably charges my body capacitor up to 150V DC just like static charges do).


My first thought is that when 2 lamps are in series they see roughly 60 vac across each-below strike voltage.  When you touch the junction, the lamp connected to the hot lead sees 120 VAC so it lights, but then its maintaining voltage is lower so it allows the 2nd lamp to see a high enough voltage to strike?
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16416
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #182 on: March 09, 2015, 11:45:27 am »

My first thought is that when 2 lamps are in series they see roughly 60 vac across each-below strike voltage.  When you touch the junction, the lamp connected to the hot lead sees 120 VAC so it lights, but then its maintaining voltage is lower so it allows the 2nd lamp to see a high enough voltage to strike?

It's always interesting when we get an unexpected result, forcing us to learn something or stay confused.

To explore or model what was going on I experimented with applying real capacitors from the junction of the neon lamps to neutral.

exp #1 .001uF cap... the line lamp glows steadily with ocassional flashes from neutral lamp.
exp #2 240 pF cap    both lamps remain dark.
exp #3 470 pF cap    both lamps glow similar to human body.

So I look approximately like a 470 pF cap... (IIRC from googling this the human body is more like 100-300pF ).

Yes, I guess we have an obscure scenario where first the line lamp fires, charging up the small cap until the voltage across that lamp is too low to sustain it, but by then there is enough voltage to fire the neutral lamp.

With too low C this never fires to get started. (the high brightness lamps I bought are 95V min... normal brightness lamps fire at 65V). The 1000pF is enough that the neutral doesn't fire, or just blinks randomly, and 470 pF is like Goldilock's porridge, just right to light both. An odd coincidence that the human capacitance falls in the sweet spot range for this obscure mechanism***.

The bad news is that none of this helps me by itself. and reinforces that I need to buffer myself to look like a larger capacitance or lower Z... With lower Z I would get the proper Line lamp lit.  I now have parts (400V mosfets) so I can make the buffer. I suspect with the buffer I can use daylight bright LEDs and operate at lower impedance so ghost currents are ignored. The neon lamps can glow with as little as single digit microamps but very dimly. Of course I need to build this to confirm there are no more surprises.

I'm pretty sure the world doesn't need a $20 outlet checker when the $3 neon lamp appears to work adequately for general testing. FWIW I just probed the floating ground pin on my kitchen GFCI outlet and the neon lamp glows, so this is not definitive and susceptible to ghost voltages/currents. Note: I already replaced my old electric kettle that was the worst offender for leaking current to ground, but floating grounds will likely report hot in other real systems too. So maybe the world does need a better outlet tester.   

JR

*** circuit designers are often haunted by marginally stable circuits that only work when you touch a component , or more insious when you put a scope probe on it (pF of capacitance). With high impedance design, sometimes your touch provides a DC path, but more often it's the capacitance. I have heard horror stories of military R&D projects where a finished prototype shipped with a scope probe inside hanging off the circuit node that made it work. No doubt to meet a date deadline.   :o :o (No I would never do that.).   
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16416
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #183 on: March 12, 2015, 01:45:09 pm »

Another update, I finished breadboarding my "touch" buffer using a pair of P and N power mosfets. Unfortunately it doesn't work as I hoped. I'm pretty sure the outlet on my bench is reversed polarity with floating ground, so for my first trial my buffer power supply is swinging 120V AC with 160V dc rails above and below that AC.

It is hard to put a scope probe on this but my suspicion is that the power mosfets I used have a few hundred pF of input capacitance each, so that swamps out my bodies puny couple hundred pF. So back to the drawing board, I haven't failed, I just proved another way that doesn't work.

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

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16416
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #184 on: March 14, 2015, 07:36:02 pm »

I don't want to count my chickens before they hatch but my second alternate approach appears to work (so far)... It requires a separate touch probe for each line being tested, but on my bench I can now reliably detect and indicate correct or reversed polarity power. I didn't breadboard up a ground probe but for a RPBG that ground will scan the same as any other hot lead so that should work.

I need to buy some different parts,,, I no longer need the 400V parts, I can drop down to 200V and just enough current to light a LED so the 300pF mosfet input capacitance can drop to <100 pF.  Not sure if this will help or hurt..

JR

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

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3356
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: brain storm an optimal human safety system for back line
« Reply #185 on: March 16, 2015, 04:14:42 pm »

I don't want to count my chickens before they hatch but my second alternate approach appears to work (so far)... It requires a separate touch probe for each line being tested, but on my bench I can now reliably detect and indicate correct or reversed polarity power. I didn't breadboard up a ground probe but for a RPBG that ground will scan the same as any other hot lead so that should work.

I need to buy some different parts,,, I no longer need the 400V parts, I can drop down to 200V and just enough current to light a LED so the 300pF mosfet input capacitance can drop to <100 pF.  Not sure if this will help or hurt..

JR

JR, I have already determined that using 3 neon lamps with a common touch pad has too many unpredictable interaction, so I'm also cooking up a version with 3 separate touch pads driving three separate neon lamps. One thought was a touch pad with insulated concentric circles to let fingertip resistance isolate the circuits a bit, but in my head I don't think it will work. This probably needs 3 separate touch pads for proper isolation. The problem seems to be that some unterminated lines will still have leakage current due to capacitive or inductive or some other "ive" effect. Since this needs to sniff out any condition, that could be a design killer. My 6-light tester may need a set of 3 tungsten bulbs for the original 3-light tester part, and 3 neon lamps for the "hot line to earth" test.
Logged
Mike Sokol
mike@noshockzone.org
www.NoShockZone.org

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16416
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #186 on: March 16, 2015, 06:12:03 pm »

JR, I have already determined that using 3 neon lamps with a common touch pad has too many unpredictable interaction, so I'm also cooking up a version with 3 separate touch pads driving three separate neon lamps.
+1 to 3 separate touch contacts (great minds think alike).  8)
Quote
One thought was a touch pad with insulated concentric circles to let fingertip resistance isolate the circuits a bit, but in my head I don't think it will work. This probably needs 3 separate touch pads for proper isolation.
At high impedances the finger resistance could short them together... With my approach that could serve as a lamp test (all three would light up). 
Quote
The problem seems to be that some unterminated lines will still have leakage current due to capacitive or inductive or some other "ive" effect. Since this needs to sniff out any condition, that could be a design killer. My 6-light tester may need a set of 3 tungsten bulbs for the original 3-light tester part, and 3 neon lamps for the "hot line to earth" test.

One concern I am trying to address is phantom voltages that the neon lamps can report as positive results too (like my kitchen outlet grounds that are floating).

JR

PS: I need to order new parts to reduce my input capacitance (a factor of 3)... This project is testing my understanding of the physical world around us. Not only are we a resistance and capacitance to some vague environmental ground, we are also an antenna/voltage source (I estimate a few volts near my bench). A 1Meg shunt is enough to damp this human noise voltage. Verrry interesting...
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2258
Re: brain storm an optimal human safety system for back line
« Reply #187 on: March 16, 2015, 11:49:13 pm »


PS: I need to order new parts to reduce my input capacitance (a factor of 3)... This project is testing my understanding of the physical world around us. Not only are we a resistance and capacitance to some vague environmental ground, we are also an antenna/voltage source (I estimate a few volts near my bench). A 1Meg shunt is enough to damp this human noise voltage. Verrry interesting...

I wish more of the younger generation would enjoy the discovery process.

Is high impedance necessary?  What if you lower the impedance with say 30-40k resistors connected in a y -hot to neutral, hot-ground, and neutral-ground?

Also, since you were using a common touch pad, I am guessing the neons were connected line (to be tested)-ballast resistor-neon-touchpad.  What if you changed to line (to be tested)-neon-ballast resistor-touchpad?  That would isolate the neons to some degree? 
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16416
  • Hickory, Mississippi, USA
    • Resotune
Re: brain storm an optimal human safety system for back line
« Reply #188 on: March 17, 2015, 09:38:55 am »

I wish more of the younger generation would enjoy the discovery process.
I am always happy to learn new stuff...
Quote
Is high impedance necessary?  What if you lower the impedance with say 30-40k resistors connected in a y -hot to neutral, hot-ground, and neutral-ground?
The problem is impedance to what...? Impedance between line and neutral is not a problem but between a floating ground and whatever will just weakly bond ground to that voltage. An impedance to both will raise a floating ground to V/2.

My mosfet buffers allow me to use lower impedance LED indicators on the output side, while hopefully providing a repeatable input sense contact.. That still needs to be proved. My first design was too complex and didn't work.. It is getting simpler and mostly working which is a good sign.   
Quote
Also, since you were using a common touch pad, I am guessing the neons were connected line (to be tested)-ballast resistor-neon-touchpad.  What if you changed to line (to be tested)-neon-ballast resistor-touchpad?  That would isolate the neons to some degree?

If I understand your question it's no difference for series components to change their order.

JR

PS: Another thing I am hooping for with increased sensitivity is to use a non-human stand-in for the environmental ground reference. I did not get an indication from an open line cord, but touching the plug from my electric drill worked. On reflection the drill was probably sitting on my carpet while I performed that test which might have affected it's ability to mimic a ground reference. Ideally I'd like to be able to sense hot/cold without touching meat.
Logged
Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2258
Re: brain storm an optimal human safety system for back line
« Reply #189 on: March 17, 2015, 12:11:26 pm »

If you place a relatively low impedance from a floating ground to neutral that should bleed off any phantom voltage-just like a low impedance VOM.  At least that is my thinking.

Yes, series components all have same current flow, and oder does not change that-but this is not a simple series circuit. If the neon lamps are connected to a touchpad they are interfering with each other.  Placing the ballast between the neon and the touchpad puts that impedance between the lamps so you get 2 times the ballast isolation-similar too, but more predictable than using three separate touchpads connected by your skin.
Logged
Steve Swaffer

ProSoundWeb Community

Re: brain storm an optimal human safety system for back line
« Reply #189 on: March 17, 2015, 12:11:26 pm »


Pages: 1 ... 17 18 [19] 20 21 ... 55   Go Up
 



Page created in 0.036 seconds with 22 queries.