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Measuring where quench occurs



---------- Forwarded message ----------
Date: Sun, 28 Sep 1997 08:13:13 -0600 (MDT)
From: Chip Atkinson <chip-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: Measuring where quench occurs 


From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Friday, September 26, 1997 12:02 AM
To: 	Tesla List
Subject: 	Re: Measuring where quench occurs

Tesla List wrote:
> 
> From:   Jason Judd[SMTP:Jason.Judd-at-anu.edu.au]
> Sent:   Wednesday, September 24, 1997 11:01 PM
> To:     Tesla List
> Subject:        Measuring where quench occurs
> 
> Hi all,
> 
> I have recently been watching waveforms of my coil on a scope. The scope is
> set up about 8' from the coil with a short wire on the end of the probe. I
> clearly see two notches and then a very slow low amplitude decay. By
> varying K the number of rings in each notch changes ( of couse ), but what
> am I actually seeing here does this show that the gap is quenching after
> the second notch ? I wouldn't have thought so because the secondary will
> continue to ring until the energy has been disipated ?
> 
> My tests have been carried out at low power levels so far, but I found that
> when I turned up the power sometimes I would see a third notch.
> 
> Do other people measure the quench by directly measuring accross the gap ?
> 
> Thanks,
> 
> Jason

Jason,

Since not everyone can receive graphics, I've attempted to show the
envelope of the waveform you're seeing via ASCII art. For best results,
select a fixed width font (like courier) to display the ASDCII charts
below. 

Your pickup wire is giving you a representative sampling of your
secondary's output voltage. When the primary gap initially fires, the
electrostatic energy stored in the tank cap (inital "bang" energy)
transfers from the primary tank circuit to the secondary resonator and
toroid, then back to the primary. This energy tranfer process continues,
at lower amplitudes, until the gap stops conducting/reigniting. The
sequence for your coil is shown in CASE 1 below. Based on your
description, your coil is actually quenching on the third primary
"notch", since the primary current has minimums at points T2, T4, and
T6. 


At T1           Primary Spark Gap initially fires   

T1 to T2        Tank cap's Energy transfers to secondary, completing 		
at T2. An "ideal" quench would occur at this point

T2 to T3        Remaining Energy transfers to primary, completes at T3
                if gap reignites after point T2

T3 to T4        Remaining energy transfers to secondary, completes at T4 
                while gap continues to fire

T4 to T5        Remaining Energy transfers to primary, completes at T5
                if gap reignites after point T4

T5 to T6        Remaining energy transfers to secondary, completes at
T6                 while gap continues to fire

T6              Gap now fails to reignite ("quenches"), blocking
energy                  in the resonator/toroid. Secondary rings down at
rate     		governed by streamer loading and secondary Q

Typically, the secondary's ringdown time is relatively long but all
secondary energy has dissipated long before the arrival of the next
"bang". From an energy standpoint, each bang is an independent event. 
 
CASE 1:
Suboptimal Quenching at 3rd notch:

           .
       .       .               .   . 
    .              .        .           .              .
  .                  .   .                 .     .             .
 .                    . .                   . .                      .
._______________________._____________________._________________________ 
 .                    . .                   . .                      . 
  .                  .   .                 .     .             .
    .              .        .           .              .
       .        .               .   . 
           .  

^          ^           ^          ^          ^         ^         ^
|          |           |          |          |         |         |
T1         T2          T3         T4         T5        T6    Exponential
                                                              Ringdown
Gap      All     All Remaining  
Fires   P -> S      S -> P
        Xfr'ed      Xfr'ed

    
CASE 2:
Optimal Quenching at 1st Notch:

           .
       .            .               
    .                       
.                                            
.                                  .          
 .                                               .   
-------------------------------------------------------------.
 .                                               . 
  .                                  .     
    .                        .
       .            .    
           .                  (decay time not to scale)    

            ^                    ^
            |                    |

      Max Secondary        Ringdown rate is dependent upon      
      Energy Tranfer       the degree of breakout (streamer
  (Ideal Quench Point)     energy losses) and Secondary Q


In case 2, quenching has occurred at the first notch, trapping maximum
energy in the secondary. The ringdown period is typically much longer
than the ringup period (T1 to T2). The heavier the streamers, the more
rapid the ringdown. If breakout is prevented, the ringdown period will
be very long if you have a high Q secondary. BTW, 1st notch quenching is
very difficult to achieve, particularly at higher coupling coefficients.

I hope this helps a bit in better understanding what you're seeing.

Safe coilin' to you, Jason!

-- Bert --