Table of Contents
Advertisement
(1)
The Comparator.
A functional block diagram of the comparator unit is
provided in Figure
25.
The analog voltages to be compared are applied to the in-
put of the amplifier, which is provided with a special feedback network within the
comparator.
This feedback network consists of two back-to-back diodes, and allows
the high-gain of the amplifier under open loop conditions
to provide highly accu-
rate switching.
The output of the comparator unit is provided at two terminals
designated DIG 1 and O.
Only two voltage levels are available at these terminals,
zero volts or +5 volts.
In addition, the voltages at the I and 0 terminals are
always complementary (opposite from each other).
For ,example, if the voltage at
the summing junction of the comparator amplifier is positive, the circuit will pro-
duce plus 5 volts at the 1 terminal and zero volts at the 0 terminal.
These levels
are referred to as binary ONE and binary ZERO respectively.
If the voltage at the
summing junction of the amplifier goes negative, the state of the circuit reverses
and a binary ZERO appears at the I terminal while +5
volts~inary
ONE) appears at
the 0 terminal.
In addition to the analog inputs, binary logic levels may be connected to the latch
(LTH) or unlatch (UNLTH) terminals to control the operation of the comparator.
If
a binary ONE (+5 volts) is applied to the latch terminal, the output of the com-
parator amplifier is effectively disconnected from the comparator unit, and the
binary output levels from the comparator remain in their. previous states.
If a
binary ZERO (ground or O'volt) is applied to the unlatch terminal, the analog in-
put voltages regain control of the comparator.
The binary ZERO applied to the un-
latch terminal overrides the binary ONE at the latch terminal, so that if both ~
applied together, the comparator responds to analog input voltages.
The binary output levels from the comparator unit may be connected to either or
both of the electronic switch units, trunked to another, computer, or used for other
special purposes.
(2)
The Electronic Switch.
Two electronic switches are included in the
comparator unit.
Figure 26 provides a block diagram of a switch unit.
Each switch
consists of a four-diode gate; precision input and feedback resistors; and a trans-
istorized control circuit.
When a binary ONE (+5 volts) is applied to the
digital input terminal, the gatelli opened and an analog current is passed through
the gate to the associated amplifier.
The analog input is normally connected to
the appropriate IN
terminal, then coupled through an input resistor and the gate
to the amplifier.
For special applications, the analog input may be connected to
the GJ (gate junction) terminal, which by-passes the input resistor and applies
the current directly through the gate to the amplifier summing junction.
Circuits
and patching for the electronic comparator are summarized in the appendix.
c.
Dual Function Switch Group 2.127
The Dual Function Switch Group consists of a patching module, Type 12.264, and a
Dual Function Switch Assembly, Type 20.366.
The function switches are mounted on
the Control Panel and are terminated on the patching module which is located in the
middle row of the patch panel.
Each function switch is a single-pole, double-throw
switch with a center-off position.
The upper switch is terminated on the upper
50
Advertisement
Table of Contents
