Fluke PM6681 - Page 26

Block
Diagram
Description
General
The PM 6681
Timer/Counter consists of
three
main units:
-
Front unit
-
Main board unit
-
Rear panel unit
Several options can
be added, these are:
-
Prescalers
(1.3
GHz PM
9621,
2.7
GHz
PM
9624,
4.2 GHz PM
9625B, and 4.5
GHz
PM
9625)
“
Oscillators
(TCXO PM
9678B and oven
oscillators’
PM 9690 and PM
9691)
-
Rack
mount adapter (PM
9622)
-
Rear panel
inputs (PM
9611/81)
The
chassis of the counter
consists of a front piece
molded
in aluminum, an aluminum
rear panel, and three
aluminum
profiles that
hold the
front and rear panels
together. This
unit can be
slid
into the aluminum
cover of the
instrument.
The front unit
contains all
functions needed for
the user
communication. A
flat
cable connects the
front
unit to the
main board unit,
and
the molded
front-piece
screws onto
the two
aluminum
profiles.
Most
functions, such as the
following, are
placed
on
the
main
board:
-
Input amplifiers
with
trigger level
circuits
-
Power supply
-
Measurement logic
“
Microcomputer
circuitry
-
GPlB-bus
“
Analog
output
“
External reference input
-
External
arming
input
Some
outputs, such as the
TRIGGER
LEVEL
and PROBE
COMPENSATION
VIEW
outputs are
directly mounted on
the main board.
The
rear
panel unit is an
aluminum
panel with
a
number
of
mounted connectors.
Most of
the
connectors
are soldered
directly
to the main board. The
rear panel
screws onto
the
two aluminum profiles.
NOTE:
Simplified extractions
from the
Schematic diagrams
are used
in
this
chapter. For
complete information,
see
Chapter
8,
Schematic
Diagrams.
4-2
Block
Diagram
Description