Thanks for the thorough explanation.
Regards
Titoy
----- Original Message -----
From: <HI100@xxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Thursday, January 18, 2001 3:40 PM
Subject: Re: [OM] T20 inop on Auto
> litefoot@xxxxxxxxxxxxxxx writes:
>
> << Would you mind explaing briefly what and how a quench tube works? How
does
> it limit light output if as mentioned, the T20 actually makes a full dump
of
> output each time regardless of aperture?
> >>
>
> The point I was making in my followup post was that the T20 does NOT use a
> quench tube it uses an SCR series circuit.
>
> Early style auto flashes using quench tubes were invented and patented by
> Harold Edgerton, a professor at MIT.
>
> These flashes work like this:
> 1) a large capacitor is charged to a voltage usually between 330V and
550V .
> 2) this capacitor is connected across the flash tube with a current
limiting
> inductor in series .
> 3) when the flash is triggered by the camera, a large voltage (at low
> power) is applied to the outside of the tube triggering a very high
current
> to flow through the Xenon gas in the tube and emit light for a period of
time
> determined by the inductance in series with the tube and the energy stored
in
> the capacitor.
> 4) a second "quench" tube somewhat similar to a normal flash tube (with
> lower voltage cutoff ) is connected in parallel with the main flash tube
> 5) A light sensor detects light reflected back from the subject to be
> photographed and generates an integrated light signal proportinal to the
> accumulated light over time. When a predetermined amount of light has been
> recieved the second quench tube is triggered which diverts current from
the
> main tube and hence extinguishes it's light output. Diverting the
remaining
> energy from the flash capacitor into the internal quench tube wastes the
> remaining energy making it necessary to almost completely recharge the
> capacitor from scratch.
>
> In a more modern "series type circuit" like the T32/20 etc a very high
> current semiconductor switch like an SCR, GTO thyristor or IGBT is
connected
> in series with the flash tube. This switch is switched off (commutated
off)
> to interupt the current flow through the tube when enough light has been
> recieved. This saves the energy left in the capacitor for the next flash
and
> can greatly shorten the capacitor recharge time.
>
> The trigger signal used to stop the light output is often still called the
> "quench signal" even though flash quenching operates a bit differently in
a
> modern flash.
>
> Regards,
> Tim Hughes
> >>Hi100@xxxxxxx<<
>
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