U.S. patent number 3,573,777 [Application Number 04/782,382] was granted by the patent office on 1971-04-06 for combustion products detector control apparatus.
This patent grant is currently assigned to Honeywell Inc.. Invention is credited to Arlon D. Kompelien.
United States Patent |
3,573,777 |
Kompelien |
April 6, 1971 |
COMBUSTION PRODUCTS DETECTOR CONTROL APPARATUS
Abstract
A combustion products detector system having a central station
and one or more remote ionization type sensing stations
interconnected to the central station by a three conductor line and
further having a solid-state end-of-line supervision circuit which
reports back on one line that all three lines are in good
condition. The remote station has an ionization detector across
which is maintained a substantially constant voltage and through
which a current flows, the current being reduced in the presence of
combustion products. The circuit is specially designed to provide
an output current which changes in direct proportion to the sensor
current.
Inventors: |
Kompelien; Arlon D. (Richfield,
MN) |
Assignee: |
Honeywell Inc. (Minneapolis,
MN)
|
Family
ID: |
25125882 |
Appl.
No.: |
04/782,382 |
Filed: |
December 9, 1968 |
Current U.S.
Class: |
340/629;
356/439 |
Current CPC
Class: |
G08B
17/11 (20130101); G08B 29/06 (20130101) |
Current International
Class: |
G08B
29/06 (20060101); G08B 17/11 (20060101); G08B
29/00 (20060101); G08B 17/10 (20060101); G08b
017/10 () |
Field of
Search: |
;340/227,228,237,228.
(1)/ ;340/237 (S)/ ;356/207 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Partridge; Scott F.
Claims
I claim:
1. Control apparatus for a products-of-combustion detector
comprising:
a source of potential having a first terminal and a common
terminal;
means for developing a first reference potential with respect to
said common terminal;
means for developing a second reference potential with respect to
said common terminal;
differential amplifier means having an input stage comprising a
field effect transistor, said amplifier means including said means
for developing a first reference potential;
further amplifier means comprising second transistor means which
has a plurality of electrodes including a control electrode and a
first and second current carrying electrode, said first electrode
being conductively connected to said first terminal and said second
electrode being connected by junction means and impedance means to
said second reference potential;
a sensing circuit connected in controlling relation to said field
effect transistor signal electrode including products-of-combustion
sensing means and resistive feedback means, said feedback means
being connected to said junction means and normally biasing said
field effect transistor signal electrode to a potential equal to
said second reference potential whereby the potential existing
across said feedback means remains of essentially the same
magnitude as the potential existing across said impedance means so
that the current flowing through said impedance means is
proportional to the current flowing in said high impedance sensing
circuit.
2. The apparatus of claim 1 in which said amplifier means, junction
means and impedance means further comprises a potentiometer, one
terminal of which is conductively connected to said second
transistor means, the other terminal of which is conductively
connected to said second reference potential and the adjustable
wiper of which is connected to said resistive feedback means, so
that when over a period of time said products-of-combustion sensing
means loses its original degree of sensitivity, its effective
impedance increases and said normal biasing potential tends to
change, a readjustment of said adjustable wiper to restore said
normal biasing potential simultaneously changes the gain of said
amplifier means to compensate for the decreasing sensitivity of
said products-of-combustion sensing means.
3. Control apparatus for use with a high impedance condition sensor
comprising:
direct coupled amplifier means having a first and a second terminal
to be energized from a source of potential and further
including;
a field effect transistor having a pair of current carrying
electrodes and a signal electrode, the signal electrode providing a
potential sensitive input stage;
a reference voltage of a predetermined magnitude with respect to
one of said terminals;
an output transistor having current carrying electrodes and a
control electrode;
resistive means having first and second extremities and an
intermediate tap;
a series circuit connected from said first terminal to said
reference voltage, said circuit comprising the current carrying
electrodes of said output transistor in series with said tapped
resistive means, one of said electrodes being connected to said
first terminal and one of said extremities being connected to said
reference voltage, the other electrode and second extremity being
connected together;
a sensing circuit having a current flow therethrough and connected
in a controlling relation to said amplifying means input stage,
said circuit including a products-of-combustion sensor of the
ionization chamber-type connected between said input stage and said
second terminal, and resistor feedback means connected to said
input stage, said current flowing through said resistor feedback
means and ionization chamber biasing said signal electrode to a
voltage which is equal to said predetermined potential magnitude;
and
conductive connecting means connecting said resistor feedback means
to said intermediate tap of said resistive means so that the
potential existing across said resistor feedback means changes with
and remains of substantially the same magnitude as the potential
existing across said resistive means portion between said tap and
said reference voltage whereby the amplified current flowing
through said resistive means is proportional to the current flowing
in said sensing circuit.
4. The apparatus of claim 3 in which said resistive means comprises
a potentiometer, one terminal of which is connected to said output
transistor, the other terminal of which is conductively connected
to said reference potential and the adjustable wiper of which is
connected to said resistor feedback means, so that if the
sensitivity of said condition sensor decreases whereby its
effective impedance increases, and the biasing of said signal
electrode tends to change from said predetermined potential
magnitude, a readjustment of said adjustable wiper to restore said
signal electrode to said predetermined potential magnitude
simultaneously increases the gain of said amplifier means to
compensate the control apparatus for the decreasing sensitivity of
said condition sensor.
5. The apparatus of claim 3 wherein said sensing circuit is subject
to undesired leakage currents to surrounding structure, the
apparatus further comprising: guard ring means energized from said
reference voltage and positioned to effectively isolate said
sensing circuit from the surrounding structure to eliminate said
leakage currents.
6. The apparatus of claim 3 in which said reference voltage
comprises:
a tapped voltage divider network energized from said first and
second terminal; and
further transistor means having its input electrodes connected
between a tap on said voltage divider network and one terminal of
impedance means the other terminal of which is connected to said
second terminal whereby said reference potential is maintained
across said impedance means.
Description
SUMMARY OF THE INVENTION
A combustion products detector system having an ionization type
sensor which is to be operated at a constant voltage and through
which a current flows, the current being reduced as the presence of
combustion products increases. The circuit associated with the
sensor is especially designed to provide an amplified output
current the magnitude of which changes in direct proportion to the
sensor current.
DESCRIPTION OF THE DRAWINGS
In the drawings, FIG. 1 is a diagrammatic representation of the
system of a combustion products detector;
FIG. 2 is a schematic representation of the combustion products
detector sensing head and the associated electronics; and,
FIG. 3 is a graphical representation of certain operating
characteristics of the apparatus disclosed in FIG. 2.
DETAILED DESCRIPTION
This apparatus is concerned with a superior alarm which will
provide reliable fire alarm and more specifically will provide an
alarm in the presence of combustion products such as smoke visible
or invisible. A solid-state end-of-line circuit provides line
supervision of all three conductors between central station and the
remote sensing stations, this line supervision intelligence being
transmitted back to the central station on one of the three lines.
The remote sensor stations have an ionization type detector which
is maintained at a constant voltage and through which a minute
current flows, the current being reduced in the presence of
combustion products. The ionization detector current amplifier
circuit is of a special stabilized type to provide an output
current which changes in direct proportion to the sensor
current.
Referring now to FIG. 1, there is disclosed a supervisory or
central station receiver 10 and a plurality of remote sensing units
or remote sensing stations coupled by a three conductor line and
terminating in a unique end-of-line line supervision apparatus. The
central station has a pair of power terminals 11 and 12, terminal
11 being positive with respect to terminal 12 and providing a
regulated voltage, and a third terminal 13 for receiving the signal
current which is indicative of sensed conditions. Remote conductors
14, 15 and 16 are connected to terminals 11, 12 and 13,
respectively, and make contact with terminals 20, 21 and 22,
respectively, of each of the remote sensors which here have been
identified as sensors No. 1, No. 2 and No. 3.
At the end of the remote line, here shown at sensor No. l, there is
connected an end-of-line (E.O.L.) unit which comprises connected
between conductors 14 and 15 a series circuit including an
impedance means or resistor 23, a junction 24 and an impedance
means or resistor 25. Connected in parallel with the resistor 23 is
an emitter-base circuit of a PNP transistor 26. Transistor 26
operates as a current control means and the collector circuit of
the transistor 26 is connected through a current limiting impedance
means or resistor 27 to the conductor 16. This end-of-line unit is
effective to provide a current on line 16 to terminal 13 of the
receiving unit which indicates that all three lines 14, 15 and 16
are in good condition. Under normal conditions, that is, conditions
of clean air free from combustion products or smoke, the only
current flowing in the conductor 16 is due to the E.O.L. circuit.
If any one of the three lines 14, 15 or 16 becomes open, the
current from the collector of transistor 26 is interrupted. An open
condition of line 15, for example, would remove the bias from
transistor 26 turning it off and reducing the current to receiver
terminal 13.
The central station receiver 10 has apparatus which is sensitive to
and responds to either an increase in current on conductor 16 to
terminal 13 or a decrease in such current as is known in the art.
Although this apparatus may take many forms and be in the form of
solid-state circuitry or relays, for explanatory purposes, the
circuit within station 10 from terminal 13 is a voltage source
transistor 18, a marginal relay 30 and a normally energized relay
31 to the negative terminal 12. Relays 30 and 31 might also be in
the form of a three position relay which is normally biased to the
center position and which will move to a third position with an
increase in current and drop to a first position with a decrease in
current. In the embodiment shown, the normal current flowing
through transistor 26, resistor 27 and conductor 16 is sufficient
to maintain relay 31 energized but is not sufficient to energize
marginal relay 30. An increase in current will cause marginal relay
30 to be energized to indicate alarm and a decrease in current will
cause the normally energized relay 31 to drop out and indicate
trouble. By referring to sensor No. 1, it can be seen that in the
event of the sensing of smoke or combustion products, a partial
short will be placed across the conductors 14 and 16. This is, in
effect, a resistive circuit in parallel with transistor 26 and
resistor 27 so that the current flowing in conductor 16 towards
terminal 13 will be increased.
Referring now to the schematic diagram of FIG. 2 which discloses
the individual condition sensor circuits, power input terminals 20
and 21 are connected respectively, to conductors 34 and 35.
Connected across conductors 34 and 35 is a multistage direct
coupled amplifier means including a differential amplifier
comprising a field effect transistor Q1 and NPN transistor Q2. The
FET provides a high impedance input current, and has a potential
sensitive signal or gate electrode. The drain D of transistor Q1 is
directly connected to the emitter of transistor Q2 at a junction 36
which is further connected through a common impedance means or
resistor 37 to the negative conductor 35. A bias circuit for the
transistor Q2 is a tapped voltage divider network from conductor 34
to conductor 35 including a resistor 40, a potentiometer 41 and a
resistor 42. The adjustable wiper of potentiometer 41 is directly
connected to the base electrode of the transistor Q2. The collector
electrode of transistor Q2 is connected through a junction 43 and
resistor 44 to the positive conductor 34.
In parallel with resistor 44 is the emitter-base circuit of a PNP
transistor Q3, the base electrode being directly connected to
junction 43. The collector electrode of transistor Q3 is connected
through further impedance means including a potentiometer 45, and a
variable resistor 46 to a reference potential junction 47. A
resistor 50 connects junction 47 to the negative conductor 35. The
junction 47 is connected to the emitter of an NPN transistor, the
base of which is connected to the junction 42a of the voltage
divider, whereby current flows through the base-emitter of
transistor Q4 and resistor 50 to keep the potential at junction 47
maintained at a reference potential or fixed level E1.
The adjustable wiper of potentiometer 45 is connected through a
high impedance resistive feedback means 49, which may be in the
order of 10,000 megohms, to the gate electrode of FET transistor
Q1. The gate electrode of the transistor Q1 is also connected
through a high impedance ionization chamber 51 to the negative
conductor 35. This combination by suitable adjustment of
potentiometer 41 biases the gate electrode to a predetermined
potential magnitude which is the same as E1. The sensor 51 is a
combustion detector of the ionization chamber type, and may be, for
example, of the type shown in the copending application of Skildum,
Ser. No. 657,826, filed Aug. 2, 1967, and assigned to the same
assignee as the present invention.
The sensor 51 has a single sensing chamber formed by a cylindrical
cathode and a centrally located pinlike anode which carries a
radioisotope serving as a source of beta particles. In operation,
when smoke enters the interelectrode space, a decrease in current
is observed. A guard ring for the high impedance anode of the
sensor 51, the feedback resistor 49 and the gate of Q1 is connected
to the junction 47 and is biased by the reference potential E1
developed across resistor 50.
The collector electrode of transistor Q4 is connected by means of a
conductor 60, a junction 61 and a resistor 62 to conductor 34. The
resistor 62 provides the bias for a further transistor Q5, which
has its base directly connected to junction 61 and its emitter
connected by a resistor 63 to the conductor 34. The collector of
transistor Q5 is connected to the input of a discriminator to be
described below. The discriminator comprises two normally
nonconductive transistors Q6 and Q7, transistor Q6 being an NPN
type transistor and Q7 being a PNP type. A circuit path may be
traced from the conductor 34 through a resistor 64, the
collector-emitter of transistor Q6, output terminal 22, the
emitter-collector circuit of transistor Q7, and through a resistor
65 to the negative conductor 35. A further biasing portion of the
discriminator may be traced from the conductor 34 through a
resistor 66, a junction 67 which is directly connected to the base
electrode of transistor Q7, a resistor 68, a junction 69, and
resistor 70 to the negative conductor 35. The collector electrode
of Q5 is directly connected to the base electrode of transistor Q6
and to the junction 69.
OPERATION
In considering the operation of the system disclosed in FIG. 1, let
it be assumed that all of the sensors are enveloped in clean air,
that is, there is an absence of products of combustion such as
smoke in the environment of the sensors. Under these conditions,
the current I.sub.sig. flowing into terminal 13 is determined by
the magnitude of resistance 27 and the voltage between terminals 11
and 13. It may be seen that a current will flow from positive
terminal through conductor 14, resistors 23 and 25 and conductor 15
to terminal 12 to thereby bias to a saturated state of conduction
the E.O.L. transistor 26. The resulting current flowing in the
conductor 16 will be limited not by the transistor but by resistor
27. The magnitude of I.sub.sig. is of such a value that relay 31 is
energized and marginal relay 30 is not energized. If any of the
sensors detects the presence of combustion products there will be,
in effect, a resistive path connected between terminals 20 and 22
to parallel the E.O.L. current and increase the value of I.sub.sig.
on conductor 16. An increase in current on conductor 16 will be
effective to actuate the marginal relay and operate the alarm
controlled by the marginal relay. A decrease in the value of
I.sub.sig. caused by an open in one of the conductors 14, 15 or 16
or by trouble in one of the sensors will allow relay 31 to drop out
and actuate the trouble indicator in the central station receiver
10.
Turning now to the operation of FIG. 2, it should first be noted
that there are several requirements which the operating circuit
must meet. A first of these requirements is that the voltage
existing across the ionization sensing element 51 between anode and
cathode remain constant. It is also a necessary requirement that
the circuit be capable of being calibrated for decreasing sensor
cell-sensitivity wherein the gain of the amplifier is increased as
the circuit is recalibrated.
The ionization chamber-type combustion products detector has a pair
of spaced anode and cathode electrodes wherein the anode carries
thereon a radioactive source of beta particles such as Ni 63 for
rendering the air in the chamber conductive and causing an
ionization current in the interelectrode space. The magnitude of
the ionization current depends upon whether the ions are formed in
pure gases such as air, or in gases that are mixed with products of
combustion such as air mixed with smoke and the various gases given
off as a result of combustion. The ions are produced in the space
between the electrodes by means of the radioactive source. To
insure stable operation, an electrostatic shield is provided by
means of a third electrode surrounding the first two
electrodes.
An overall view of the quiescent operation of the circuit of FIG. 2
shows a constant current flowing through resistor 37 with this
current being split between currents flowing through the FET
transistor Q1 and transistor Q2. Similarly, a constant current is
flowing through the resistor 50 with this current being the sum of
the currents flowing through transistors Q3 and Q4. The current
flowing in transistor Q5, which controls the discriminator, is a
function of the current in transistor Q4. Under normal operating
conditions, that is, when there is no smoke being sensed by the
sensor 51, neither of the discriminator transistors Q6 nor Q7 is
conductive.
Two reference potentials are maintained in the circuit with respect
to negative conductor 35, the first reference potential E.sub.1
being at junction 47, that is, the constant voltage across resistor
50 is maintained by the fact that the voltage drop from base to
emitter of transistor Q4 is approximately 0.5 of a volt, and the
base electrode of transistor Q4 is connected to a fixed point on
the voltage divider comprising resistors 40, 41 and 42. Because the
transistor Q4 maintains a constant potential at junction 47, the
resistor 50 may be thought of as a constant current generator, if
desired. The transistors Q3 and Q4 are both normally conductive and
it should be apparent that with a constant current flowing through
the resistor 50 a change in the conduction of transistor Q3 results
in an equal and opposite change in the conduction of transistor
Q4.
The second reference potential E.sub.2 at junction 36 is maintained
by the transistor Q2 since its base electrode is connected to the
adjustable wiper of potentiometer 41 of the voltage divider. The
junction 36 is thus clamped to a voltage of about 0.5 volts less
than the setting of the wiper on potentiometer 41. The fixed
reference voltage E.sub.2 at junction 36 results in a constant
current flowing through the resistor 37 which may be thought of as
a constant current generator, if desired. Thus the differential
amplifier comprising transistors Q1 and Q2, both of which are
normally conductive, divide up the current flowing through resistor
37 and an increase in the current through transistor Q1 results in
an equal and opposite decrease in the current flowing through
transistor Q2.
In a typical operating circuit as shown in FIG. 2, the resistive
feedback means 49 may be of a value in the order of 10,000 megohms
and the clean air impedance of sensor 51 may be in the order of
27,500 megohms so that about 180 .times.10.sup.-.sup.12 amperes
flows through the sensor 51 from anode to cathode, and a voltage of
5 volts is maintained at the gate electrode of the transistor Q1.
Approximately 0.8 of a volt bias exists between gate and drain of
transistor Q1 and therefore the reference E.sub.2 is maintained at
5.8 volts by adjusting the wiper on potentiometer 41 to a setting
of approximately 6.3 volts. Since the voltage at the gate of
transistor Q1 is 5 volts, the guard ring surrounding the anode of
the cell 51 and the feedback resistor is also maintained at 5
volts, this reference E.sub.1 being maintained by having the base
electrode of Q4 tied to a voltage of approximately 5.5 volts on the
voltage divider.
The guard ring is necessary because of the extremely high impedance
circuit to the gate of FET transistor Q1 to prevent leakage
currents from disturbing the balance of the system.
Let it now be assumed that products of combustion become present in
the area of ion sensor 51. The presence of products of combustion
in the chamber of the sensor reduces the ionization current flow
through the sensor and in effect, increases the interelectrode
impedance. Turning momentarily to a consideration of FIG. 3, it may
be seen that curve a shows the current versus voltage curve for
clean air of sensor 51 while curve b shows the current versus
voltage curve for air which includes a given quantity of combustion
products. This reduction in current through the sensor will tend to
increase the potential at gate G of transistor Q1 with the result
that the current flowing through the output circuit of transistor
Q1 tends to increase. As has been explained above, any incremental
increase in the current flowing through Q1 results in an
incremental decrease of the same amount in the collector current of
transistor Q2. Direct coupled amplifier Q3 amplifies this
incremental reduction in current of Q2 so that less current flows
through Q3 and resistors 45 and 46. The potential at the wiper of
potentiometer 45 moves in a less positive direction, that is, the
potential E4 is reduced. The voltage E3 across feedback impedance
49 is also reduced to restore the potential at gate G towards its
steady state value.
A consideration of FIG. 2 reveals that the voltage E3 across
feedback resistor 49 is equal to the voltage E4 which exists
between the wiper of potentiometer 45 and the reference potential
E1 at junction 47. This results because the voltage at the gate of
Q1 and the reference voltage E1 at junction 47 are initially set to
be identical, the upper terminal at which E3 and E4 are measured
(the wiper of potentiometer 45) is common, and the voltages E3 and
E4 increase and decrease together and remain equal. As a result,
the current I.sub.out flowing at the output of the primary portion
of the amplifier, that is, through impedance or resistors 45 and
46, is directly proportional to the current through sensor 51,
which is also the current through feedback resistor 49. It is
recognized that the current I.sub.out is of much larger magnitude
than the current in the sensing circuit.
The reduction in current I.sub.out through transistor Q3, and
resistors 45 and 46 results in an increase in collector current of
output conditioning amplifier transistor Q4 by an amount equal to
the decrease through Q3, since a constant current flows through
resistor 50. As a result, transistor Q5 conducts more, its
collector potential changes in a positive going direction and
discriminator transistor Q6 becomes conductive. Current then flows
from the positive conductor 20 through the resistor 64 and
transistor Q6 to the conductor 22. This has the effect of
increasing the value of I.sub.sig. to pull in the marginal relay 30
and actuate the alarm.
After several years of operation, depending upon the half-life of
radioactive material in the sensor 51, the sensitivity of the
sensor 51 will be decreasing, i.e., its interelectrode impedance
increases, and the curves showing current versus voltage for clean
air and for air containing products of combustion may now be
represented by curves a' and b' of FIG. 3. It will be understood
that there is a very gradual shift downward in the slope of these
curves as the radioactive element becomes less active. It will
further be noted from FIG. 3 that the curves a' and b' are not
separated by as large a current difference as are the original
curves a and b so that it may be said that the sensitivity of the
sensor 51 is decreased. The circuit is designed so that a
recalibration of the input to correspond to the new quiescent clean
air operating point of the sensor will also increase the gain of
the amplifier. When a recalibration becomes necessary, the wiper of
voltage divider 45 is moved in a downward direction to a less
positive setting so that the original voltage of the gate (in the
example, 5 volts) is again obtained. It will be noted that the
signal developed at the output of transistor Q3 appears across
resistors 45 and 46 but that as the wiper of potentiometer 45 is
moved downwardly, a lesser portion of the signal developed across
these resistors is applied as negative feedback through the
resistor 49. With less negative or degenerative feedback applied,
the gain of the amplifier is increased to compensate for the
reduction in sensitivity of the element 5l.
If during operation, the sensor 51 should somehow become shorted or
if various elements of the circuit should fail, so that the
conduction of transistor Q5 is reduced below its normal value the
potential at junction 69 will be less positive and transistor Q7
will receive a forward bias through resistor 68 whereby it becomes
conductive. This provides a resistive path between conductors 22
and 21 through the transistor Q7 and resistor 65 which has the
effect of reducing toward zero the current I.sub.sig. which flows
through conductor 16 to the terminal 13. The normally energized
relay 31 then drops out to give a trouble indication.
Resistor 65 is chosen so that the current through Q7 can cancel the
E.O.L. current flowing to terminal 13 of the central station
without excessive current through Q7. Resistor 64 is chosen so that
when transistor Q6 is switched on, it produces sufficient
additional current to terminal 13 to cause the marginal relay to
operate for alarm even if another sensor had already produced a
trouble indication. This allows alarm operation of the system even
while waiting repair of a trouble condition in one of the
sensors.
* * * * *