Table of Contents
Advertisement
10. SIGNAL COMPARATORS AND FUNCTION SWITCHES
a.
Relay Comparator
(1)
General Description.
The Relay Comparator consists of a high-gain
amplifier and a double-pole, double-throw relay.
The amplifier compares a variable
input voltage to an arbitrary reference input voltage and operates the relay when
the weighted algebraic sum of the input voltages is negative.
The relay is de-
energized when the weighted algebraic sum of the input voltages is positive.
The circuit configuration of the relay comparator is shown in Figure
23a~
The
signal input is applied to IN
l
; the reference input is applied to IN
2
.
When the
inputs produce a negative voltage at the summing junction of the amplifier, the
amplifier energizes the relay and the relay arms are connected to the minus con-
tacts.
The relay is de-energized when the summing junction is positive or when
no inputs are applied; the relay arms are connected to the plus contacts.
Since
the input resistors, Rl and R2, have different values, the voltages applied to INI
and IN2 have different weights in their effect on the summing junction voltage.
Therefore, the setup procedure described below must be followed if precise switching
levels,are desired.
(2)
Adjustment of Voltage Switching Level.
To obtain a precise voltage
switching level, say +5 volts, proceed as follows:
(~)
Refer to Figure 23b.
Connect a coefficient potentiometer to the
input of an amplifier and adjust the wiper until the output of
the amplifier is at the desired switching level (+5 volts in this
example).
Connect the output of the amplifier to the INI termin-
ation of the comparator.
(£)
Connect the appropriate computer reference voltage (-10 vdc in
this case) to a second potentiometer.
Connect the wiper to the
IN2 termination.
(£)
Adjust the wiper of the second potentiometer until switching
occurs.
The switching action can be observed by patching ref-
erence voltage into a relay arm and monitoring the voltage on
a contact with the voltmeter.
(~)
Remove the amplifier input to INI and apply an arbitrary signal
input.
b.
Electronic Comparator
The Model 40.538 Electronic Comparator .(Figure 24) is a versatile high-speed
switching device.
The unit operates in conjunction with external operational
amplifiers, and consists of a comparator unit which produces binary output levels,
and two electronic switch units.
These units may be combined or used independ-
ently, depending on the circuit requirements and the patching arrangements.
47
Advertisement
Table of Contents
