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RE: Series or Parallel resonant ? ( was: New pics and scope waveforms)




On Mon, 20 Dec 1999 22:12:41 -0700, Tesla List wrote:

>  Original Poster: Dale Hall <Dale.Hall-at-trw-dot-com> 
>  
>  Hi Malcom and All listening,
>  
>  Oops, I stand corrected, 
>  brain was thinking generator perspective, spoke LC perspective :(  
I dont quite understand all of this, but have identified an error below. 
>  Malcom correctly states (re-phrased), 
>  at resonance for both Series and Parallel excited generator modes
>   circulating LC current is maximum producing maximum voltage at Xc=XL.
>   Line current, i.e. from generator source, is opposite.
>  
>  Series resonance:
>  1.) defined as the Freq where XL=Xc, only 1 freq meets this.
>  2.) Current source generator drive is a lowZ in Series w/LC.
>  The Generator passes the high series circulating current, adding energy. 
>  XL=Xc cancel and generator internal resistance adds to
>   inductors Rdc and Cap ESR.
>  Since the generator is in series providing new current plus passing 
>  circulating current,
>   the voltage across LC is limited only by the ability of the
>   generator to source current via low internal impedance (else lower Q) or
>   less than infinite Q due to losses (load producing parallel resistance
>   which can be transformed to represent equivalent series resistance).
>  
>  Parallel resonance:
>  1.) defined as 
>      a.) minimum generator current, 
>      b.) maximum impedance, or
>      c.) V & I in phase

V & I are only in phase in series resonance, in parallel resonance they are
180 degrees out of phase. This is what gives its maximum impedance, the 
reactive currents are almost continually opposite to the impressed voltage.
The nodal rules of amperage entering and leaving a junction apply, and it is
the instantaneous DIFFERENCE of reactive currents on each branch that is the
measured input amperage, which is q times less than the actual circulating
tank circuit, hence the term, resonant rise of amperage in a tank circuit
>      a., b., c., each represent separate distinct (but close) resonant

>  frequencies for Q=<10, above which the three converge to one freq.
>  Applic note: Q before spark load is likely >10, afterward <10.
>  The voltage across LC is supplied by the parallel generator.
>  
>  2.) is modeled as a Voltage source in parallel i.e. across LC. 
>  LC Reactance is highest at resonance, diminishing before and after.
>  So, generator source line current is highest either above or below Fres.
>  Approaching Fres a parallel generators source line current dips to a
minimum
>  
>  due to rising voltage across LC as circulating current increases to max
>  (XL-Xc=0 so Igen = Vin/Rdc).
>  
>  Hope I have this right now, and that it is relevant !
>  
>  Regards, Dale

Hope I got it right, too. It would seem to me that the induced currents on
the secondary,similar to that on a transformer, are 180 phased as regards
its causitive source by mutual induction. Thus the currents on the secondary
are 180 out of phase with that primary current from the tank circuit. The
currents on the secondary are given an increased resonant rise of voltage
because that side of the equation is a series resonance, Not another tank
circuit. In this way we can view both the resonant rise of amperage occuring
on the tank circuit, simultaneous to a resonant rise of voltage on the
secondary.

>  
>  -----Original Message-----
>  From: Tesla List [mailto:tesla-at-pupman-dot-com]
>  Sent: Sunday, December 19, 1999 4:23 PM
>  To: tesla-at-pupman-dot-com
>  Subject: RE: Series or Parallel resonant ? ( was: New pics and scope
>  waveforms)
>  
>  Original Poster: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> 
>  
>  Hi Dale,
>  
>  > Original Poster: Dale Hall <Dale.Hall-at-trw-dot-com> 
>  > 
>  > Hi Malcom,
>  > Thanks for your response.
>  > Please see my earlier reply to Richie's feedback.
>  > 
>  > I disagree with your response:
>  
>  > >The truth is that both 
>  > >types exhibit a current maximum and a voltage maximum across 
>  > >their individual components at resonance. 
>  > 
>  > I believe the essence of whether LC parallel components
>  >  are series or parallel resonant depends upon where 
>  >  the source generator is in the circuit.
>  
>  How one classifies the circuit depends on how one applies energy 
>  to it, that I agree with. However, any tuned circuit has a circulating 
>  current which is a maximum at resonance and byu Ohm's law, the 
>  voltage across each individual component in it is a maximum also.
>  
>   Series resonance: generator is part of the series LCR.
>  > All Rdc's are in series.
>  > 
>  > Parallel resonance: generator is across "Both" L and C physically
>  parallel.
>  >   The generator sees L's resistance different than in the series model
>  >   in that C is across the generator, L+RdcL is across the generator.
>  
>  The generator sees the shunt impedance of the circuit in this case 
>  whereas in series resonance, the generator sees the ESR. 
>  
>  > In this context, I stand by my original statements.
>  
>  I must differ on the contention that voltage is minimum across a 
>  parallel circuit at resonance.
>  
>  > I agree this is all very confusing, I hoped to make it clear (?) sorry.
>  > 
>  > There appears to be easy confusion stemming from components in parallel
>  > contrasted to how they are driven,
>  >   generator in series with parallel components (Igen=max) or
>  >   a generator driving across parallel components (Igen=min).
>  
>  Agree
>  
>  > In your radio set front end example
>  >  assuming parallel resonance,
>  >  the incoming signal (a generator) appears across both L & C at same
time,
>  >  the voltage must be minimum else the current couldn't be minimum
>  >  to represent minimum load to the incoming signal at Fo.
>  
>  Aha!  Suppose the voltage was a minimum. The circuit would 
>  present a near short circuit to the aerial. Aerial current is a minimum 
>  as you say but the circulating current in the tuned circuit is a 
>  maximum.
>  
>   I agree with 
>  > >the secondary is more driven at Fr than by an impulse,
>  > sorry if I was misleading....
>  > 
>  > even the Primary simply and highly selectively at Fr extracts the
>  > fundamental
>  >  of the square impulse provided by a spark gap switch.
>  >  Current injected by the gap switch is accepted by the Pri LC
>  sinusoidally,
>  >  not as rectangular impulse, due to the frequency selectivity of the LC
>  >  and that rectangular waves are composed of sinewaves which LC is able
to
>  > isolate.
>  >  The LC actually highly rejects all energy outside the fundamental
>  resonant
>  > freq.
>  >  High order harmonics see a very high impedance producing little
current
>  >  due to their divergence from the highly selective resonant frequency. 
>  > 
>  > Experiment: set up a lowZ (simulating Rgap) square wave generator
driving
>  >  a HI-Q toroid inductor and mica cap in series resonance.
>  >  The fundamental sinewave provides most of energy at resonance
benefiting
>  > from 
>  >  Vpk_fund = 4/Pi*Vpk_squarewave peak {flat top] amplitude !
>  > 
>  >  Placing a high value load resistor across LC demonstrates
>  >   affects of De-Q'ing, equivalent series resistance, etc.
>  >   simulating Spark loading,  without sparking !
>  
>  I think a resistor is a poor representation of an arc discharge as the 
>  characteristic is wrong.
>  
>  Regards,
>  Malcolm
>  <snip>
>  
>  
>  
>  


Binary Resonant System
http://www.insidetheweb-dot-com/mbs.cgi/mb124201





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