
Circuit Switchers and High-Current Generator Breakers with Isolating Contacts
A-26
72A-1898 Rev. A 11/01
Monday
, November 26, 2001 1:09 pm
When contact #2 is still open (step-down voltage is not applied to
point A), all capacitors are charged according to the circuit parameters
(C
2
in series with C
1
//C
3
– see Figure A.26 on page A-25). As soon as the
step-down voltage is applied, the capacitors discharge (C
1
in series, with
C
2
//C
3
) and due to the current through Rg1, the voltage at point B drops.
When the discharge process is completed, and the capacitors are
charged according to the new circuit condition, the potential at point B
returns (no current through Rg1).
The voltage at point B is monitored by the comparators that follow the
open-to-close transition of contact #1. The temporary voltage drop can
be misinterpreted as a change in the state of contact #1. This
phenomenon results in
cross-talk
between the contact operation
measurement channels. The cross-talk occurs within the module and
between all the modules in a phase. It produces erroneous contact state
transition information.
Although it is desirable to distinguish between real contact activity and
cross coupled signals with 2
µ
s resolution, this is neither a practical nor
realistic task because fast contact bounces and cross-talk appear as
identical events. The cross-talk is dealt with by using a Digital
Discriminator.
The Digital Discriminator is a digital filter circuit located on each
channel of the Main Contact Board
.
The device is located downstream of
the comparator circuit, and qualifies the data before it is stored in
memory. The Digital Discriminator operates upon any type of contact
activity, and qualifies both Main Contacts and resistor switch data.
The filter time can range from 4 to 100
µ
s and is set by the Test Plan in
2
µ
s increments.
The Digital Discriminator circuit is triggered when a bounce is first
detected, and sets up a
window
in time equal to the Filter Time. Bounces
with durations equal to or greater than the Digital Filter Time are passed
through and stored in memory as valid contact data, while bounces with
durations less than the Filter Time are rejected and not recorded. The
TDR9000 does, however, flag these events so they are not used when
calculating the resistor value.
Содержание TDR9000
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