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Патент USA US3073966

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Jan. 15, 1963
R. R. HOGE
3,073,956
NUCLEAR INSTRUMENTATION
Filed April 30, 1959
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INVENTOR.
ROBERT R. HOGE
BY
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ATTORNEY
Jan. 15, 1963
R. R. HOGE
3,073,956
NUCLEAR INSTRUMENTATION
Filed April 30, 1959
Z‘Sheets-Sheet 2
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BIAS (INPUT) VOLTAGE
FIG-2
INVENTOR.
ROBERT R. HOGE
ATTORNEY
ice?
Patented Jan. 15, 1963
1
3,073,956
cillator; the bridge components having a shield or con
ductive enclosure therearound with the secondary wind
Bendix tlorporation, a corporation of Delaware
ing leads extending through the conductive enclosure and
with the extended portion of the secondary winding being
NUCLEAR INSTRUMENTATEQN
Robert R. Hoge, Farmington, Mich, assignor to The
Filed Apr. 30, 1959, Ser. No. 8139360
12 Claims. (Cl. 250-—83.1)
shielded by an outer conductor connected to the bridge
shield and with the transformer core, primary winding,
and oscillator being without the conductive enclosure.
This invention pertains to nuclear instrumentation
It is a still further object to provide a method of am
wherein a signal from an ionization chamber which estab~
plifying small electrical signals comprising the steps of
lishes a current in response to neutron bombardment is 10 feeding said signal between a pair of semiconductor de
greatly ampli?ed, and the method of amplifying said
signal.
vices, applying a level of alternating voltage across the
semiconductor devices below the conduction level of the
It is an essential object of this invention to provide a
devices, amplifying, phase inverting, and rectifying the
nuclear instrumentation which receives a very small sig
output across the semiconductor devices, and applying
nal from an ionization chamber and accurately ampli?es 15 through a logarithmic device the recti?ed output between
this signal with the tolerances of the instrumentation
the semiconductor devices.
components being large and the instrumentation controls
being simpli?ed.
These and other objects will become more apparent
when a preferred embodiment of this invention is de~
It is another object of this invention to provide in such
scribed in connection with the drawings in which:
instrumentation, a bridge circuit having a pair of adja~ 20
FlGURE 1 is a block schematic diagram of a nuclear
cent connected arms each of which has a semiconductive
reactor instrumentation system; and
device acting as voltage variable capacitors placed there
‘FIGURE 2 is a plot of the capacitances of the semi
in in a common direction, and with these arms connected
conductive devices as they vary with bias voltage.
to a pair of resistive arms which are connected to each
This invention pertains to instrumentation for ampli
other through a rheostat slide wire, and with a high fre
fying very small currents to usable currents and has the
quency alternating current source being between the
advantages of low power requirements, mechanical and
semiconductive half of the bridge circuit and the resistive
electrical stability, long life, simplicity of adjustment,
half of the bridge circuit; a rheostat contact slidable along
low initial and maintenance costs, and accuracy of ampli
the rheostat wire between the resistive arms so that the
bridge may be balanced by movement of the contact along
the rheostat wire, whereby the application of an input
signal at a point between the semiconductive devices will
bias these devices, changing their capacitance, to unbal
ance the bridge, thereby providing an ampli?ed output
?cation. This invention provides an instrumentation sys
tern wherein a semiconductive bridge circuit is used
to invert a small direct current to an ampli?ed alternat~
ing current which is further ampli?ed, phase inverted,
and then recti?ed to a direct current. The bridge por
tions are effectively shielded and a “feedback” or shunt
signal corresponding to the unbalance resulting there 35 circuit is provided to stabilize the instrumentation action
resulting in highly accurate performance.
from.
It is a further object of this invention to provide in
The bridge comprises two semiconductive devices act
such a bridge a conductive enclosure for the bridge com
ing as voltage variable capacitors connected in a common
ponents to shield them from the high frequency alternat
direction in adjacent arms of a bridge circuit. A high
ing current source which comprises a shielded coaxial 40 frequency oscillator source is connected across the arms
cable connected across the semiconductive arms and
extending through the enclosure, the coaxial cable being
and a rheostat means is also connected across the arms
wound as a secondary about a transformer core located
with the rheostat pointer being connected to the output.
Moving the pointer until the output is zero provides a
outside the conductive enclosure, and with the transformer
simple balancing means and bridge component charac
core having a primary winding connected to an oscillator
teristics can be easily balanced out.
The current output of an ionization chamber is con
nected between the semiconductive devices and biases
one semiconductive device in a forward direction and the
other semiconductive device in a reverse direction to op
device.
It is a further object to connect to such a bridge in the
above instrumentation system an ampli?er, a phase in
verter, a demodulator, and a feedback or shunt circuit
which comprises a diode connection between the output
of the demodulator and the input to the bridge circuit
which converts the output voltage to a logarithmic func~
tion of the input current.
It is a further object to provide an inverter bridge hav
positely affect their capacitances which unbalances the
bridge circuit resulting in an ampli?ed alternating output
corresponding to the unbalance. Inputs as low as 10-10
amperes are sufficient to unbalance the circuit to get a
corresponding output which can be ampli?ed as high as
ing in one half two semiconductor arms with each arm 55 twentyfold without the use of a separate ampli?er. The
having a semiconductor device acting as voltage variable
capacitors connected in a common direction, and in the
other half two resistive arms, with the diagonal between
the semiconductive and resistive arms including a high
frequency alternating current source, and with a rheostat 60
wire connection connecting the two resistive arms so that
inverter bridge is connected to an ampli?er which may
amplify in the order of 1000 times and then to a phase
inverter, the output of which is connected through a diode
back to the input to stabilize the ampli?cation of the
instrument.
Referring now to the drawings and particularly FIG
movement of a rheostat pointer will balance the output
URE 1, a block schematic diagram of an instrumentation
of the bridge and application of a direct current input sig_
system of this invention is seen. A high voltage source
nal between semiconductive devices will bias the semicon
29 is connected through a shielded cable 22 to the outer
ductive devices, changing their capacitances and un 65 surface of ionization chamber 24. A chamber electrode
balancing the bridge resulting in an alternating output
26'extend from within the chamber 24 through a shielded
corresponding to the unbalance.
cable 28 and a conductive enclosure 30 to inverter bridge
It is a further object to provide in the bridge circuit
32. Enclosure 30, While represented by a dashed line,
of the previous paragraph a high frequency alternating
is continuous in nature and completely encloses the ele
current source comprising a transformer core with the 70 ments indicated therein. The material used for enclosure
secondary winding connected along the aforementioned
39 may be brass or any other suitable shielding material.
diagonal and the primary winding connected to an os
Bridge 32 is connected to ampli?er 34 which in turn is
3,073,956
4
3
voltage to be V1, reference to FIGURE 2 will show that
connected to phase inverter and demodulator 36. A feed
back line 37 from the output of phase inverter ‘and de
modulator 36 to the input of bridge 32 contains a diode
the capacitances of the semiconductors will assume new
values uubalancing the bridge circuit. Each different
value of the input voltage will result in different capaci—
38 therein. Of course, more than one diode may be used
and in addition, as later explained, other type electrical
components could serve in its place for particular pur
tive values of the semiconductors 44, 46 as determined
by the curves 44a, 46a, respectively. This unbalance will
result in a corresponding alternating output of the bridge
circuit to ampli?er 34 and with the embodiment shown,
poses.
The bridge circuit 32 comprises a pair of lines 40, 42
between which are a pair of connected semiconductive
ampli?cation may be up to 20‘ times. If a minus input,
devices 44, 46 about which are shown in dashed lines 10 such as V2, is inserted at point 78, then a phase reversal
variable capacitors 43, 50, respectively. As will become
will occur at the bridge output with the absolute value of
the input corresponding to the amplitude of the alter
nating current output.
condensers varying according to the input voltage applied
The ampli?er 34 ampli?es the signal as desired, which
to the devices 44, 46. Semiconductors manufactured by 15 may be 1000 times, ‘and passes the ampli?ed signal to
Hughes Aircraft Company and having a product number
a phase inverter 36 which recti?es and inverts all voltages
going thereto 180°, reversing their sign. This ampli?ed,
HC-700S and manufactured by' Paci?c Semiconductor,
Inc. with product number V~100 have been successfully
reversed voltage is applied at one terminal of a semi
evident, the semiconductive devices 44, 46 act as variable
condensers in the bridge circuit, with the capacity of the
conductor 38 which has its other terminal connected to
used in the circuit. It is desirable to use a semiconductor
which has a high rate of capacitive change per incre 20 the bridge circuit 32 input. In this manner, a feedback
ment of bias or input voltage to provide the desired sensi
is applied at the input of the bridge circuit 32 so that
tivity. Also, the semiconductors should be chosen to
the output is converted to a logarithmic function of the
have very small leakage current.
input current at point '78. The ampli?er 34 supplies
The lower half of the bridge circuit comprises resist
power gain su?icient to drive other equipment, such as
ances 52, 54, 56 with resistance or rheostat 54 having 25 meters, automatic controls, alarms and so forth.
an adjustable contact connected to line 42. The values
Brie?y, the operation is as follows. A high voltage
of the resistances 52, 54, 56 may be respectively 300, 100
from source 20 is applied to the outer surface of chamber.
and 300 ohms.
24 creating a potential gradiant from the walls of cham
A high frequency oscillating source is connected across
ber 24 to electrode 26. When chamber 24 is sub
the semiconductive and resistive portions of the bridge 30 ject to neutron bombardment, the gaseous medium is
circuit. Connected between points 60 and 62 of the bridge
ionized resulting in current conduction to the electrode
circuit is a secondary winding 64 which extends through
26 and to line 40 of bridge circuit 32. This causes a bias
the conductive enclosure 30 and is wound about a trans
voltage across semiconductors 44, 46 which in turn varies
former core 65. Those portions of the secondary Winding
the capacitance of the semiconductors according to the
outside of the enclosure 30 are shielded by an outer 35 respective semiconductor curves shown in FIGURE 2.
cable 68 which is connected to the enclosure 30. The
transformer core 65 is energized by primary 66, which is
This in turn unbalances the bridge and the high fre
quency alternating voltage across points 60 and 62 is’
impressed in an amount corresponding to the unbalance:
across the bridge output to ampli?er 34. The signal
frequency of the voltage impressed at points 60 and 62 40 here is greatly ampli?ed and passed to a phase inverter‘
may be for a particular application approximately 10
36 where the signal is reversed in sign, recti?ed and fed
kilocycles and it has been found that advantageous opera
to a feedback line 37 and across diode 38. The output
connected across oscillating source 67, which may gen
erate a square, sinusoidal or other periodic wave. The
tion is obtained when the operating root mean square
is available across resistor 80 and since a diode is in
voltage between points 60 and 62 is between 100 and
the feedback line through which the input current ?ows,
200 millivolts with very satisfactory operation occurring 45 the output will be in a logarithmic ratio to the input.
at 1'50 millivolts.
If desired, a resistor could be substituted for diode 38
so that the output would be in linear proportion to the
Further elements of the bridge circuit include resist
input.
ance 70 which may be 750 kilohms and which is used to
isolate the output from the input. A resistance 72
In this description circuit 37 has been de?ned as a
shunting the bridge represents the leakage resistance of 50 “feedback” circuit and is a feedback circuit insofar as the
the semiconductors 44, 46 and is for the semiconductors
voltage from inverter and demodulator 36 is fed back
mentioned approixmately 1010 ohms. Also located in
to one terminal of diode 38. The current flow in circuit
line 40 is a blocking condenser 74 which blocks the direct
37 is in the direction of the arrow of diode 38 and for
current input from the alternating current output going
this reason the circuit has also been referred to as a
to ampli?er 34. Inductance 76 is adjusted so that the
capacitive effects of the bridge as seen by ampli?er 34
are substantially reduced.
The operation of the bridge circuit will be more easily
understood with reference to FIGURE 2 which shows a
pair of curves 44a and 46a representing the plots of 60
capacitance, measured along the ordinate, of semicon
ductors 44, 46, respectively, versus the bias or input
' voltage masured along the abscissa.
The ?rst step in the operation of the circuit is to
adjust potentiometer 54 until the bridge output is bal
anced or zero. With this single adjustment the bridge
output is balanced and any irregularities in the circuit
components or semiconductors are balanced.
Because
of this balancing, the circuit components and assembly
“shunt” circuit and might be referred to as a “feed
around” circuit.
The level of the alternating voltage impressed between
points 60 and 62 may assume various values and is below
the conduction values of the semiconductors. The semi
conductors act, therefore, as voltage responsive capaci
tors and not as conduction devices.
Although this invention has been disclosed and illus
trated with reference to particular applications, the prin
ciples involved are susceptible of numerous other appli~
65 cations which will be apparent to persons skilled in the
art. The invention is, therefore, to be limited only as.
indicated by the scope of the appended claims.
Having thus described my invention, I claim:
1. Nuclear instrumentation system comprising an ion-v
costs are reduced and simpli?ed since tolerances may 70
ization chamber responsive to reactor neutron bombard
be correspondingly large. If an input current, as from
ionization chamber 24, is inserted at point 78 in line
40 in a positive direct-ion, semiconductor 44 will be
biased in a reverse direction and semiconductor 46 will
ment and emitting a direct current signal proportional
thereto, a bridge circuit having two semiconductor de
vices connected in a common direction, an alternating
be biased in a forward direction. Assuming the input 75 current source being placed across said semiconductor
5
3,073,966
devices, the voltage output of said alternating current
source being less than the conduction level of said semi
conductor devices, resistive means being placed across
said semiconductor devices, an output contact being con
nected to said resistive means, bridge input means con
necting said ionization chamber and a point between
said semiconductor devices, with the capacitances of
said semiconductor devices varying according to the
means comprising a conductive enclosure for shielding
?rst portion of said alternating current source from said
semiconductor devices, said resistive means and said
secondary windings.
4. Nuclear instrumentation system comprising an ion
izing chamber responsive to neutron bombardment and
emitting a direct current signal proportional thereto,
abridge circuit having two series connected semiconductor
amount of input voltage applied therebetween to un
devices connected in a common direction, an alternating
balance said bridge circuit and correspondingly in?uence 10 current source being placed across said semiconductor
the bridge output, output blocking means being in said
devices, the voltage output of said alternating current
bridge input means, amplifying means being connected
source being less than the conduction level of said semi
to said output contact, a phase inverter and demodulator
conductor devices, resistive means being placed across
being connected to the output of said amplifying means,
said semiconductor devices, an output contact being con_
and a stabilizing circuit connected from the output of 15 nected to said resistive means, bridge input means con
said phase inverter and demodulator to the bridge input
necting said ionization chamber and a point between said
means on the input side of said output blocking means.
semiconductor devices, with the capacitances of said
2. Nuclear instrumentation system comprising an ion
semiconductor devices varying according to the amount
ization chamber responsive to neutron bombardment and
of input voltage applied therebetween to unbalance said
emitting a direct current signal proportional thereto, a 20 bridge circuit and correspondingly in?uence the bridge
bridge circuit having two series connected semiconductor
output, output blocking means being in said bridge input
devices connected in a common direction, an alternating
means, amplifying means being connected to said output
current source being placed across said semiconductor
devices, the voltage output of said alternating current
contact, input blocking means being placed between said
output contact and said amplifying means, a phase in
source being less than the conduction level of said semi 25 verter and demodulator being connected to the output
conductor devices, resistive means being placed across
of said amplifying means, logarithmic conversion means
said semiconductor devices, an output contact being
being in a circuit connected from the output of said phase
connected to said resistive means, bridge input means
inverter and demodulator to the input means of said
connecting said ionization chamber and a point between
bridge circuit on the ionization chamber side of said
said semiconductor devices, with the capacitances of 30 output blocking means, said alternating current source
said semiconductor devices varying according to the
amount of input voltage applied therebetween to un
balance said bridge circuit and correspondingly in?uence
having a ?rst portion comprising a magnetic core, pri
mary winding and oscillator means, said primary wind
ing being wound about said core and excited by said
oscillator means, secondary windings being wound about
the bridge output, output blocking means being in said
bridge input means, amplifying means being connected 35 said core and connected across said semiconductor de
to said output contact, a phase inverter and demodulator
vices, conductive shielding means comprising a conduc
being connected to the output of said amplifying means,
tive enclosure for said semiconductive devices, said re
a stabilizing circuit connected from the output of said
sistive means, and said secondary winding.
phase inverter and demodulator to the input means of
5. Nuclear instrumentation system comprising an ion
said bridge circuit on the ionization chamber side of 40 izing chamber responsive to neutron bombardment and
said output blocking means, diode means being in said
emitting a direct current signal proportional thereto, a
stabil'ming circuit for current flow in a direction from
bridge circuit having two series connected semiconductor
said input means, said output contact being adjustable
devices connected in a common direction, an alternating
along said resistive means to provide a balancing means
current source being placed across said semiconductor
for said bridge circuit.
3. Nuclear instrumentation system comprising an ion
izing chamber responsive to neutron bombardment and
emitting a direct current signal proportional thereto, a
bridge circuit having two series connected semiconductor
devices connected in a common direction, an alternating
current source being placed across said semiconductor
devices and having an operating voltage range between
100 and 208 millivolts, root mean square, resistive means
devices, the voltage output of said alternating current
source being less than the conduction level of said semi
conductor devices, resistive means being placed across
said semiconductor devices, an output contact being con—
nected to said resistive means, bridge input means con
necting said ionization chamber and a point between
said semiconductor devices, with the capacitances of said
semiconductor devices varying according to the amount
of input voltage applied therebetween to unbalance said
bridge circuit and correspondingly influence the bridge
output, output blocking means being in said bridge input
means, amplifying means being connected to said output
contact, input blocking means being placed between said
being placed across said semiconductor devices, an output
contact being connected to said resistive means, bridge
input means connecting said ionization chamber and a
point between said semiconductor devices, with the
capacitances of said semiconductor devices varying ac
output contact and said amplifying means, a phase in
cording to the amount of input voltage applied there
verter and demodulator being connected to the output
between to unbalance said bridge circuit and correspond 60 of said amplifying means, a feed circuit connected from
ingly in?uence the bridge output, output blocking means
the output of said phase inverter and demodulator to
being in said bridge input means, amplifying means being
the input means to said bridge circuit on the ionization
connected to said output contact, a phase inverter and
chamber side of said output'blocking means, said alter
demodulator being connected to the output of said
nating current source having a ?rst portion comprising
amplifying means, a feed circuit connected from the 65 a magnetic core, primary winding and oscillator means,
output of said phase inverter and demodulator to the
said primary winding being wound about said core and
input means of said bridge circuit an the ionization
excited by said oscillator means, secondary windings be
chamber side of said output blocking means, logarithmic
ing wound about said core and connected across said
conversion means being connected in said feed circuit,
semiconductor devices, conductive shielding means com
said alternating current source having a ?rst portion com~ 70 prising a conductive enclosure for said semiconductive
prising a magnetic core, primary winding and oscillator
means, said primary winding being wound about said
core and excited by said oscillator means, secondary
windings being wound about said core and connected
across said semiconductor devices, conductive shielding
devices, said resistive means, and said secondary winding,
said conductive enclosure including an outer shielding
cable for that portion of the secondary winding extending
outside of said enclosure and wound about said core.
6. Nuclear instrumentation system comprising an ion
3,073,956
8
izing chamber responsive to reactor neutron bombard
ment and emitting a direct current signal proportional
thereto, a bridge circuit having two series connected
semiconductor devices connected in a common direction,
an alternating current source being placed across said
semiconductor devices, resistive means being placed
across said semiconductor devices, an output contact
‘being connected to said resistive means, bridge input
nected to ‘the output of said amplifying means, a feed
back circuit connected from the output of said phase
inverter to the input means of said bridge circuit, said
resistive means in said bridge circuit at one of said out—
put connections, one output connection being an adjust
able contact along said resistive means to provide a bal~
ancing means for said bridge circuit.
9. Nuclear instrumentation circuit means comprising
means connecting said ionization chamber and a point
a bridge circuit having in each of two arms thereof a
tances of said semiconductor devices vary'ng accordi g
connected in a common direction, said bridge circuit hav
ing two resistive arms, an alternating current source being
between said semiconductor devices, with the capaci 10 semiconductor device, said semiconductor devices being
to the amount of input voltage applied therebetween to
connected along one diagonal of said bridge circuit, the
voltage output of said alternating current source being
ence the bridge output, output blocking means being in
said bridge input means, amplifying means being con 15 less than the conduction level of said semiconductor de~
vices, amplifying means being connected across the other
nected to said output contact, input blocking
being
diagonal of said bridge circuit, input means being con
placed between said output contact and said amplifying
nected between said semiconductor devices, with the
means, a phase inverter and demodulator being connected
capacitances of said semiconductor devices varying ac
to the output of said amplifying means, a diode being in
a circuit connected from the output of said phase in 20 cording to the amount of input voltage applied there
between to unbalance said bridge circuit and correspond
verter and demodulator to the input means to said bridge
ingly in?uence the bridge output, resistive means in said
circuit on the ionization chamber side of said output
bridge circuit at one of said output connections, said one
blocking means, said alternating current source having a
output connections being an adjustable contact along
?rst portion comprising a magnetic core, primary wind~
unbalance said bridge circuit and correspondingly in?u‘
ing and oscillator means, said primary winding being
wound about said core and excited by said oscillator
means, secondary windings being wound about said core
and connected across said semiconductor devices, con
ductive shielding means comprising a conductive en
25 said resistive means to provide a balancing means for
said bridge circuit.
‘10. Nuclear reactor instrumentation system compris
ing an ionizing chamber responsive to reactor eutron '
bombardment and emitting a direct current signal pro
closure for shielding said ?rst portion of said alternating 30 portional thereto, circuit means for receiving and invert
ing said signal to provide an ampli?ed alternating cur
current source from said semiconductive devices, said
resistive means and said secondary windings, said alter~
nating current source having a voltage in the range of
100~—200 millivolts, root-mean-square.
rent output, and having an operating voltage range be
tween lGO and 2.00 millivolts, root mean square, said
circuit means comprising a bridge circuit having two
35 semiconductor devices connected across said semicon
‘7. Nuclear instrumentation system comprising an ion
ductor devices in a common direction, an alternating cur
ization chamber responsive to reactor neutron bombard
rent source being placed across said semiconductor de
ment and emitting a direct current signal proportional
vices, resistive means being placed across said semicon
thereto, a bridge circuit having in each of two arms
ductor devices, an output contact being connected to said
thereof, a semiconductor device, said semiconductor de
vice being connected in a common direction, said bridge 40 resistive means, bridge input means being connected be
tween said semiconductor devices, with the capacitances
circuit having two resistive arms, an alternating current
of said semiconductor devices varying according to the
source being connected along one diagonal of said bridge
amount of input voltage applied therebetween to unbal
circuit, the voltage output of said alternating current
once said bridge circuit and correspondingly in?uence the
source being less than the conduction level of said semi
bridge output, output blocking means being in said bridge
conductor devices, amplifying means being connected
input means, amplifying means being connected to said
across the other diagonal of said bridge circuit, input
output contact, input blocking means being placed be
means connecting said ionization chamber and a point
tween said output contact and said amplifying means, a
between said semiconductor devices, with the capaci
phase inverter and demodulator being connected to the
tances of said semiconductor devices varying according
output of said amplifying means, a diode being in a feed
to the amount of input voltage applied therebetween to.
circuit connected from the output of said phase inverter
unbalance said bridge circuit and correspondingly influ
and demodulator to the input of said circuit means on
ence the bridge output, a phase inverter and demodula
the ionization chamber side of said output blocking
tor being connected to the output of said amplifying
means, said alternating current source having a ?rst por
means, a shunt circuit being connected from the output
tion comprising a magnetic core, primary winding and
of said phase inverter and demodulator to the input
oscillator means, said primary winding being wound
means to said bridge circuit.
about said core and excited by said oscillator means, sec
8. Nuclear instrumentation system comprising an ion
ondary windings being wound about said core and con
ization chamber responsive to reactor neutron bombard
nected across said semiconductor devices, conductive
ment and emitting a direct current signal proportional
‘thereto, a bridge circuit having in each of two arms 60 shielding means comprising a conductive enclosure for
said semiconductive devices, said resistive means, and
thereof a semiconductor device, said semiconductor de
said secondary winding, said conductive enclosure in
vices being connected in a common direction, said bridge
cluding an outer shielding cable for that portion of the
circuit having two resistive arms, an alternating current
secondary winding extending outside of said enclosure
source being connected across said semiconductor de
vices along one diagonal of said bridge circuit, the volts 65 and wound about said core, output signal impeding means
being placed in said signal input means and input signal
age output of said alternating current source being less
means being placed in said output.
than the conduction level of said semiconductor devices,
11. Nuclear instrumentation system comprising an
amplifying means being connected across the other diag
ionization chamber responsive to reactor neutron bom
onal of said bridge circuit, input means being connected
to said ionization chamber and a point between said 70 bardment and emitting a direct current signal propor
tional thereto, a bridge circuit having two series con
semiconductor devices, with the capacitances of said
nected voltage responsive capacitors, an alternating cur
semiconductor devices varying according to the amount
rent source being placed across said capacitors, the volt
of input voltage applied therebetween ‘to unbalance said
age output of said alternating current source being less
bridge circuit and correspondingly in?uence the bridge
output, a phase inverter and demodulator being con 75 than the conduction level of said semiconductor devices,
3,073,956
resistive means being placed across said capacitors, an
output contact being connected to said resistive means,
bridge input means connecting said ionization chamber
and a point between said capacitors, with the capacitances
of said capacitors varying according to the amount of
input voltage applied therebetween to unbalance said
bridge circuit and correspondingly in?uence the bridge
output, output blocking means being in said bridge input
means, amplifying means being connected to said output
10
and demodulator to the input means to said bridge circuit
on the ionization chamber side of said output blocking
means, said alternating current source having a ?rst por
tion comprising a magnetic core, primary winding and
oscillator means, said primary winding being wound
about said core and excited by said oscillator means, sec
ondary windings being wound about said core and con
nected across said capacitors, conductive shielding means
comprising a conductive enclosure for shielding said ?rst
contact, a phase inverter and demodulator being con 10 portion of said alternating current source from said
nected to the output of said amplifying means, and a
capacitors, said resistive means and said secondary Wind
stabilizing circuit connected from the output of said phase
ings, said alternating current source having a voltage in
inverter and demodulator to the bridge input means on
the range of 100—200 millivolts, root-mean-square.
the input side of said ‘output blocking means.
12. Nuclear instrumentation system comprising an
References Cited in the ?le of this patent
ionizing chamber responsive to reactor neutron bombard
UNITED STATES PATENTS
ment and emitting a direct current signal proportional
2,088,584
Bucky ______________ __ Aug. 3, 1937
thereto, a bridge circuit having two series connected volt
2,544,928
Lahmeyer et al _______ __ Mar. 13, 1951
age responsive capacitors connected in a common direc
MacMahon et a1 ______ __ Aug. 14, 1951
tion, an alternating current source being placed across 20 2,564,626
2,581,273
Miller _______________ __ Jan. 1, 1952
said capacitors, resistive means being placed across said
2,675,484
Hepp _______________ __ Apr. 13, 1954
capacitors, an output contact being connected to said re~
2,681,430
Mouzon _____________ __ June 15, 1954
sistive means, bridge input means connecting said ioniza
2,839,678
De Witz _____________ __ June 17, 1958
tion chamber and a point between said capacitors, with
the capacitances of said capacitors varying according to 25
the amount of input voltage applied therebetween to un
balance said bridge circuit and correspondingly in?uence
the bridge output, output blocking means being in said
bridge input means, amplifying means being connected
to said output contact, input blocking means being placed 30
between said output contact and said amplifying means,
a phase inverter and demodulator being connected to the
output of said amplifying means, a diode being in a cir
cuit connected from the output of said phase inverter
2,899,561
White ______________ __ Aug. 11, 1959
2,909,662
Von Hippel et al _______ __ Oct. 20, 1959
2,917,633
2,917,717
2,955,213
2,956,234
Richards ____________ __
Thorsen _____________ __
Schaive _____________ __
Olsen _______________ __
Dec. 15, 1959
Dec. 15, 1959
Oct. 4, 1960
Oct. 11, 1960
OTHER REFERENCES
Bay: “Millimicrosecond Coincidence Circuits,” Nu
cleonics, April 1956, pages 56 to 60.
‘
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