RE: Gap Question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Luke" <Bluu-at-cox-dot-net> 

Antonio:
Thank you for taking the time to help me wrestle this concept!!
It is appreciated a lot.

Ok then the time concept can be ignored and the instantaneous values are
ok.

Is it safe to say that a device that displays negative resistance,
refers to a components ohmic value decreasing when there is an increase
of voltage or current?  And yes I realize that this would only occur at
certain areas on the V I curve.

Sorry I misinterpreted the resistor placement in your example.

Thanx

Luke Galyan
Bluu-at-cox-dot-net
http://members.cox-dot-net/bluu

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, February 25, 2004 4:13 PM
To: tesla-at-pupman-dot-com
Subject: Re: Gap Question

Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
  >
  > Original poster: "Luke" <Bluu-at-cox-dot-net>
  >
  > Antonio:
  > You mention that a relay with the coil wired in parallel with the
  > contacts can not be forced into the negative resistance area.  With
this
  > arrangement you are representing a switch that is controlled by a
  > voltage.  But you are also representing a switch that will shut off
as
  > soon as it conducts or breaks down.  The contacts will close and
short
  > circuit the coil and the contacts will open.
  >
  > A spark gap will stay on as long as the voltage is still present. So
  > coil in parallel with the contacts is not a good representation of a
  > spark gap.

I said to put a resistor in series with the contacts. In this way
the relay will not short-circuit itself.

  > To represent a spark gap you would need to make a circuit that would
be
  > a switch controlled by voltage and be able to stay on after that
voltage
  > has closed the switch like a spark gap.

A resistor in series with the relay contacts does this.

  > A better representation might be a relay with a resistor wired across
  > the normally open contacts and the coil wired in series with this
pair.

Works too, but may stress the relay coil, as the excess of current will
pass through it.

  > Applying a voltage to this circuit would result in a current limited
by
  > the series circuit of the resistor and the coil.  Increasing the
applied
  > voltage would continue increasing the current until the coil
magnetized
  > sufficiently to close the contacts.  At this point (breakdown) the
  > current in the circuit would be limited only by the coil since the
  > contacts have bypassed the resistor.  So the current would go up and
the
  > voltage applied to the circuit would be the same. So there would be a
  > negative resistance curve.

Ok.

  > So with this arrangement you have:
  > 1.      A voltage controlled switch like a spark gap.
  > 2.      A switch that stays closed after break down like a spark gap
  > 3.      A switch that displays a negative resistance characteristic.
  >
  > Just wanted to show that standard electronic components could be
wired
  > together and looked at a unit rather than the individual components
that
  > shows a negative resistance curve.
  >
  > In every mention of the term negative resistance it seems there is a
  > component of time usually implied assumed etc.  Seems one has to
realize
  > that the term negative resistance is actually referring to:

There is no time involved in this. Resistors are ideally
"instantaneous".

  > A decrease (negative) in ohmic value over a period of time when only
a
  > voltage or current is changed to the component.

?!

  > Am I on the right track here?

Ok for the relay model, but resistors are not affected by time. In the
relay model, just observe the instantaneous voltages and currents,
not considering in which order in time they appear.

Antonio Carlos M. de Queiroz