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July 9, 1946- ~
-
R. c. SANDERS. JR
2,403,615
FREQUENCY RESPONSIVE CIRCUIT
'
Filed Nov. 30, 1942
F/90M1H9U0D7/p.
Bnventor
‘Dovo-en C?anDeQ/JQ:
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Patented July 9, 194a
' 2,403,615
. r umrso STATES rA'rsnrol-"Fics
FREQUENCY RESPONSIVE CIRCUIT
Royden C. Sanders, Jr., Hightstown,_N. J., assignor '
to Radio Corporation of America, a corporation
of Delaware‘ '
Application November 30, 1942,- Serial No. 467,445
3 Claims._ -(Cl.- 175-4320) '
tion is connected to ground through to a capaci
tor 2|. The grid 23 of an ampli?er tube 25 is con- '
nected to the diode plate 19 through a resistor
21. A load resistor 28 is'connected from the an
ode IQ to the arm 3| of a tap switch 33. A plu
rality of resistors 35 are connected in series with
an adjustable resistor 31 across a direct current
source-38. The taps 38 of the switch 33 are con
be used to control motors or indicators in re
sponse to changes in‘the frequency of an alternat
ing current source of relatively low‘ power capa
2
is grounded, and the anode I! of the other sec
This invention reiates to frequency responsive
circuits, and more. particularly to a ‘system for
operating a relatively rugged relay in response to
signals of predetermined or selected frequencies.
when the input is above a preselected frequency,
the relay is operated to one position; when the
input is below’ this frequency the relay is oper
ated to another position. Thus the device may
10 nected between the resistors 35 so that an adjust
able portion of the direct current voltage may be
applied to the load resistor 29. A relay ll is con=
nected in the anode circuit of the tube 25.
One application of this system is in the control
The device operates as iollows:
of aircraft by means of a radio altimeter of the
type described on pages 86-90 of Civil Aeronautics 15 Audio frequency voltage applied across the re
bility.
'
- -
sistor I is ampli?ed in the tube l. The amplitude
of the input voltage is made high enough to cut
Bulletin No. 29, published by the Civil Aero
nautics Administration. The radio altimeter pro
vides an audio frequency output directly propor
tional in frequency to the height of the airplane
03 the tube on the negative peaks and cause satu
ration on the positive peaks. This clips the peaks
of the ampli?ed voltage, producing an output of
rectangular wave form. The time constant of
above the ground. The airplane may be con
trolled to ?y at some selected level by operating
motors connected to the elevator surfacesin re
sponse to variations in the output frequency of
the altimeter from the frequency corresponding
to the selected level. A frequency responsive re
lay system for this purpose must withstand the
vibration and acceleration forces occurring in
?ight without failure or false operation.
Accordingly, it is one object of this invention
to provide an improved method of and means for 30
the condenser 8 and the resistor ‘i is made so small
that the condenser 9 will be almost 109% dis
charged or charged in one half cycle of the high
est frequency at which this device is to operate.
The positive half cycle of the rectangular wave
causes the condenser 9 to be charged through the
diode section I3, H. The negative half cycle of
the rectangular wave discharges the condenser Si
mined value in the frequency of an alternating
through the diode section i5, 59 into the con»
denser 2| and hence stores its discharge current
in the condenser 2|. The condenser 2i discharges
through the load resistor 29, potentiometer 3i and
voltage.
the direct current source 38. The condenser e
controlling a relativelyheavy and insensitive re
lay in response to variations from a predeter
_
-
.
Another object is to provide an improved de 35 charges and discharges through a voltage range
Esw equal to the peak'to peak amplitude of the
vice which is uniformly sensitive to frequency
rectangular wave voltage across the resistor '5
variations, independent of the selected frequency.
minus any average negative voltage Ef developed
A further object is to provide an- improved
across the ‘condenser 2|. Hence every cycle,
method .of and means for controlling the damp
(Esw-t-Ej) C. Coulombs or (Esw+E.f) (C) (F)
ing of a relay or other electromagnetic device, to
amperes will be passed by the diode section 15, i9,
prevent erratic operation in response to sudden
where F is the frequency of the applied signal.
variations of the control voltage or received
signal.
and C is the capacitance of the capacitor H. H '
Eb is the positive bias potential developed between
These and other objects will become apparent
to those skilled in the art upon consideration of 45 point SI and ground, and R. is the resistance or
the following description. with reference to the
the resistor 29, then
accompanying drawing, which is a schematic cir
E‘!=Eb— (EswieEf) (C) (F) (R)
cuit diagram of an embodiment of the invention.
when
E!
is negative only. It is seen therefore
A pentode ampli?er tube i is provided, with a
grid leak 3, a self bias resistor I, and a load re
sistor 1. The plate of the tube I is coupled
through a capacitor 9 to a double diode II. The
plate I! of one diode section and the cathode I!
of the other diode section are connected to the
capacitor I. The cathode II of the ?rst section
50 that the voltage E! is the resultant some at the
positiveibias voltage Eb from point 3| to ground
and the negative voltage developed across the re“
sister 2! due to the current (Esw-l-Ef) (C) (F).
when E! is negative, the above relations hold ex
actly. However if the current (Esw+El) (C) (F)
9,408,015
-
'
4
is not su?icient to make El negative, then enough '
steady D.-C. current will flow thru the diodes
quency responsive circuit for operating a relay
in
to input of a predetermined fre
quency. a unidirectional voltage, related in mag
II, II and II, I! to maintain E! at approximately
sero volts. Thus El‘ will not vary appreciably
with frequency until the current
'
nitude to the frequency of the input, is derived. ,
An adiustable unidirectional voltage is opposed '
.
to the frequency derived voltage, and the result
ing diiference voltage is used to control an am
is large enough to cause E! to become negative. I
pli?er tube connected to the relay.
Above that point E1‘ will vary with frequency be
1 claim. as my invention:
coming more nonlinear as E] becomes an appre
1. A frequency responsive relay system com
ciable part of Esw. The rate of change of E!
with respect to frequency is:
prising a limiter, a recti?er coupled to the out
put of said limiter through a capacitor, a second
'
capacitor in series with said recti?er, a discharge
path for said second capacitor including a direct
in- 2811+ E1). we)
df
l-CJ'R
‘
i
The condenser 21 discharges through the loa
resistor II, potentiometer 3! and the direct cur
rent source 8|.
Thus the negative voltage E! increases with fre
quency, becoming nonlinear with respect to fre
quency when E! is an appreciable fraction of the
square wave voltage Esw.
The voltage at the Eb
tap ll is adjusted to a value correspondingtothe
frequency at which the relay is to beoperated.
. when the frequency is below the selected value,
‘ the grid 23 of the tube II is positive and the relay
is energized. maintaining the contacts 43 in their
ll current source connected to oppose the voltage
produced across said second capacitor by the
current ?owing through said recti?er, a second
recti?er connected across said second capackor
and said ?rst recti?er and poled oppositely there
to, an ampli?er tube with-its control grid coupled
to said discharge circuit, a relay connected in
._ the anode circuit of said ampli?er tube, and
means for adjusting the voltage of said direct
current source which is-applied to said discharge
circuit, whereby said voltage overcomes the volt;
age produced across said second capacitor at a
upper positions. When the voltage!!! becomes
slightly greater in magnitude than the voltage at
the tap II, the grid 23 becomes negative and the
anode current of the tube 2| decreases, reducing
the energization of the relay II and causing the
movable contacts 4! to go to their lower positions. '
In order to vary the frequency at which the
relay 4| is operated the tap 3|‘ may be moved to
,th
~~
then ope
'
:
contact II.
The system is
described above, cutting of! the
tube 2! as the frequency increases about the
selected value. Thus the same number of cycles
predetermined frequency or input to said limiter.
2. The method of operating a relay in response
to variations in the frequency of an alternating
voltage comprising the steps of deriving a uni
directional voltage related in magnitude to said
frequency, opposing said voltage to a second uni
directional voltage of adjustable magnitude, con- '
trolling a power circuit in accordance with the
amount by which said second voltage exceeds said ,
?rst voltage, and energizing said relay with said
power.
3. The method of operating a relay in response
to variations in the frequency of an alternating
per second deviation will actuate thereigy at any 40 voltage comprising the steps of deriving a uni
selected frequency.‘ The resistor 21 and the ca
directional voltage related in magnitude to said.
pacitor 2| are so proportioned as to have a time
constant equal to’or greater than that of the _ I
frequency, opposing said voltage to a second uni- '
directional voltage of adjustable magnitude, con
capacitor 2i and resistor 2!. This causes the
a direct current in accordance‘ with in
anode current of the tube 25 to change at the l5 trolling,
amount by which said second voltage exceeds said
same rate.with a decrease in frequency as 'it
does with an increase in frequency, preventing
erraticopcrationoftherelayll.
-
The invention has been described‘ as a fre
?rst voltage, and energizing said relay with said
current.
-
a
ROYDEN C. SANDERS, Js.
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