U.S. patent number RE29,143 [Application Number 05/637,583] was granted by the patent office on 1977-02-22 for fail-safe apparatus for checking the presence of flame in a burner.
This patent grant is currently assigned to Societa Italiana Elettronica S.p.A.. Invention is credited to Gianni Bianchini.
United States Patent |
RE29,143 |
Bianchini |
February 22, 1977 |
Fail-safe apparatus for checking the presence of flame in a
burner
Abstract
A control device for monitoring the presence or absence of a
flame through the use of an ionization tube sensitive to radiation
of a predetermined wavelength and which is emitted by the flame.
Energy storage means are employed to accumulate the signals
generated by the ionization tube. The stored energy is periodically
pulsed to discharge the stored energy in an intermittent manner
thereby delaying the generation of a signal representing the
absence of a flame. The state of the energy storage means is
digitized at the aforesaid periodic rate and is restored generally
to its undigitized form before controlling the delayed generation
of a flame-out signal.
Inventors: |
Bianchini; Gianni (Reggio
Emilia, IT) |
Assignee: |
Societa Italiana Elettronica
S.p.A. (Milan, IT)
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Family
ID: |
27273391 |
Appl.
No.: |
05/637,583 |
Filed: |
December 4, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
462190 |
Apr 18, 1974 |
03914662 |
Oct 21, 1975 |
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Foreign Application Priority Data
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May 22, 1973 [IT] |
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24389/73 |
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Current U.S.
Class: |
361/175; 340/507;
340/577; 340/578; 340/530 |
Current CPC
Class: |
F23N
5/082 (20130101); F23N 5/242 (20130101); F23N
2227/18 (20200101) |
Current International
Class: |
F23N
5/24 (20060101); F23N 5/08 (20060101); H01H
047/24 () |
Field of
Search: |
;340/228.2,227R
;431/79,24,69 ;250/372 ;307/233 ;328/6 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moose; Harry
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen
Claims
What is claimed is:
1. A flame control device usable with a detector head exposed to
the radiation of a flame to be monitored, said detector head
preferably comprising an ionization tube which develops an output
signal in the presence of flame, said flame control device
comprising:
a chain of stages being connected in cascade fashion, each stage
including at least one electrical component;
a first stage of said chain being coupled to said detector
head;
a first one of all remaining stages including dynamic coupling
means to stop the continuous components and to translate only
energy given by the alternate components of the input signal;
a second one of said remaining stages including energy storage
means for storing energy furnished by said coupling means and
generating an electrical signal representative of the signal
developed by said detector head;
a third one of said remaining stages including first chopper means
for sampling said electrical signal;
a fourth one of said remaining stages including a threshold circuit
measuring the level of the sampled signal, for developing an output
signal having a first level in the presence of a flame and for
developing an output signal of a second level within a
predetermined period after the absence of flame.
2. The apparatus of claim 1 wherein said remaining stages further
comprise a fifth stage comprising energy storage means coupled to
said threshold circuit for converting the output state of the
intermittently operated threshold circuit to a continuous
signal;
a sixth stage comprising a final output stage; and
a seventh stage comprising second chopper means for intermittently
coupling the output of said fifth stage to said final output stage
in a periodic manner.
3. The apparatus of claim 2 further comprising relay means coupled
to the final output stage.
4. The apparatus of claim 2 wherein the final output stage
comprises transformer means coupling the intermittent signal to
said relay means.
5. The apparatus of claim 1 wherein said first chopper means is
periodically operated by signal generator means whose operating
frequency controls the sampling rate of said first chopper
means.
6. The apparatus of claim 2 wherein said second chopper means is
periodically operated by signal generator means whose operating
frequency controls the sampling rate of said second chopper
means.
7. A flame monitoring device, which receives at its input a pulse
signal originating from at least one detector head exposed to the
radiation of a flame, said detector head comprising at least one
ionization tube activated by the presence of the flame, said flame
monitoring device furnishing at its output a fail-safe signal, said
flame monitoring device comprising:
a chain of stages connected in cascade fashion, each stage
including at least one electrical component and generating a proper
output signal by the dynamic operation thereof in the event an
input of that stage receives a proper signal from an output of a
previous stage;
a first stage of said chain being coupled to said detector head for
receiving and shaping a pulse signal from said tube;
a second stage of said chain including dynamic coupling means for
translating only energy contained in a pulse signal output from
said first stage and for preventing coupling of the continuous
component of said first stage output;
a third stage of said chain including energy storage and
dissipation means for storing the energy furnished by said second
stage and generating an electric signal representative of the
signal developed by said detector head;
a fourth stage of said chain including first chopper means for
sampling said electrical signal from said third stage;
a fifth stage of said chain including threshold circuit means
measuring the level of the sampled signal for developing an output
signal having a square-wave shape in the presence of said flame and
for developing an output signal having a continuous level after the
absence of said flame;
a sixth stage of said chain comprising second energy storage means
utilizing a first level of said square-wave signals from said fifth
stage for restoring its own level of energy and utilized a second
level of said square-wave signal for making said energy available
for a next following stage;
a seventh stage of said chain comprising second chopper means for
intermittently transferring the energy stored in said second energy
storage means into an eighth stage, the energy stored being
completely exhausted within a predetermined period after the
absence of said flame; and
an eighth stage of said chain utilizing the energy intermittently
made available by said sixth stage for developing an output signal
having a square-wave shape in the presence of said flame and for
developing an output signal having a continuous level within a
predetermined time period after the absence of said flame.
8. The device of claim 7, wherein said third stage includes
adjustable resistor means for calibrating the sensitivity of the
device.
9. The device of claim 7, wherein said third stage includes
switching means for selecting the sensitivity of the device.
10. The device of claim 7, wherein said sixth stage includes
current limiting means for adjusting a delay time for response to
the absence of said flame by changing the rate of energy
discharge.
11. The device of claim 10, wherein said sixth stage includes said
switching means for selecting said delay time responsive to the
absence of said flame, by changing the energy discharge rate.
12. The device of claim 7, wherein the last stage of the chain
comprises relay means whose contacts form the output signal of the
device and transformer means coupled to the output of the previous
stage for transferring energy to said relay means responsive to an
alternation of output signal levels therefrom.
13. The device of claim 7, wherein a square-wave signal generator
controls said first and second chopper means.
Description
The present invention relates to devices for controlling the
continuity of flame, for the automatic protection and the safety of
a heating system based on the detection of characteristic
radiations emitted by the flame by means of ionization tubes, in
which by effect of the incidence of radiation in a particular
wavelength range (generally ultra-violet radiation) a series of
avalanche discharges is initiated, giving rise to a train of pulse
signals.
Generally the detection systems described consist of a detecting
head, with the tube exposed to the radiation of the flame, a line
for the power supply and the transmission of the pulse signals, and
an apparatus, commonly called a control station, which supplies
power to the tube, receives the pulse signals, measures the mean
frequency of the pulses with a circuit having special
characteristics, and energizes a relay which indicates the presence
of flame, called a flame relay, when the value measured exceeds a
pre-established threshold, and de-energizes the flame relay a
predetermined short time after the disappearance of the flame.
For the purposes of safety of the heating plant it is extremely
important not only to be able to have a highly dependable detector,
such as to give signals only for the actual presence of a flame,
but independently thereof the control station apparatus which
provides for the measurement of the signals and the flame
indication must also be effectively dependable and must on no
account give false indications of the presence of a flame.
While the ionization tube, if used correctly during its period of
useful life, has an extremely high degree of dependability, it is
extremely disadvantageous to use a control station which utilizes
complex electronic circuitry in which every component, with its own
probability of failure, multiplies the probability of misprotection
of the entire apparatus against a failure.
These disadvantages existing in apparatus presently in use can be
avoided only by means of a complex system based on a mechanical
shutter, which intermittently prevents the radiation from striking
the sensitive tube. This mechanism in all cases limits the maximum
sensitivity of the detection system, and in many cases, because of
the particular high-temperature ambient in which it is situated, is
destined to break down in a short time.
In addition thereto, the de-energization of the flame relay can
occur reliably only after a period of time substantially greater
than the obturation time of a tube.
BRIEF DESCRIPTION OF THE INVENTION AND OBJECTS
The present invention pursues the purpose of realizing a new and
improved control station with a highly dependable electronic
circuit, which avoids the above mentioned disadvantages, as its
safety is already continuously controlled and does not depend on
the manner of using the sensitive tube. The apparatus of the
present invention can be connected to an ionization detector
exposed to the radiation and operating either intermittently or
continuously. In either case the flame relay is energized only when
a series of pulse signals due to ionization is reliably present at
the input, while the absence of pulses at the input and other
dangerous conditions, especially those deriving from a possible
failure of any electronic component, cause in a pre-established
maximum time the de-energization of the flame relay. Throughout the
present description that prerogative is defined as "fail-safe
reliability."
It is, therefore, one object of the present invention to provide a
circuit for measuring pulse signals coming from a transducer, such
as an ionization tube sensitive to the radiations of a flame,
supplying, for example by energization of a relay, an indication of
presence of signal and hence of flame, in a fail-safe manner.
Another object of the present invention is to provide a device for
continuously controlling in a reliable and fail-safe manner the
perfect operation of all detection circuits present in a flame
control station, for example with ultraviolet radiations, without
the necessity of having to resort to the periodical obturation of
the sensitive tube which furnishes pulse signals by effect of the
radiation of the flame.
Another object of the present invention is to provide a new and
improved circuit, particularly useful in a device for the control
of ultraviolet radiation detected by ionization tubes and the like,
which permits an extremely high maximum sensitivity, a wide
possibility of calibration of threshold levels, a constancy of
response time after the disappearance of the input pulse signals
with fail-safe reliability, but without requiring that the
operation of the tube and hence the series of discharges due to
ionization must be somehow periodically interrupted.
Another object of the present invention is to provide, with a new
electronic circuit, a flame presence signal with fail-safe
reliability and thus to make it possible to carry out, with any
frequency and in an entirely independent manner, the periodic
verification of the aging of the tube, giving an independent signal
as soon as replacement of the tube becomes necessary.
In a flame control device, with possibility of calibrating the
sensitivity and the response times, which receives input pulses
derived from one or more detecting heads exposed to the radiation
of the flame and comprising preferably ionization tubes, and which
supplies at its output a fail-safe flame signal, the above stated
purposes are achieved, according to the invention, in that the
device is formed by a main chain of individually fail-safe stages,
the first stage receiving at the input the pulse signal not
necessarily modulated by a mechanical shutter, and the chain of
main stages is constructed so that the presence of the useful
signal at the input of each single stage is indispensable to form
the useful signal at the output of the main chain, and each stage
of the main chain is a stage of dynamic cyclic operation, in which,
under the action of a periodically variable electric test signal,
which is not necessarily the same for all stages, each component of
the stage can run through, periodically and continuously, all
points of its operating characteristic, and lastly each stage is
constructed so that the useful signal at the output of the stage
does not occur when at least one component indispensable for
fail-safe reliabiity does not continuously run through, for at
least a full cycle period, all points of its operating
characteristic.
BRIEF DESCRIPTION OF THE FIGURES
The invention and the above, as well as other, objects will be best
understood from a consideration of the following description and
drawings, in which:
FIG. 1 indicates the essential structure of the fail-safe flame
detecting system according to the invention;
FIG. 2 indicates a preferential block diagram of the essential part
of the control station in an example of realization, according to
the invention;
FIG. 3 indicates more in detail and in schematic form, a preferred
execution of the entire control station, according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
According to the principles of the invention, the flame detecting
system as a whole is composed essentially as described in FIG. 1,
namely:
A detector head A, to be placed near the combustion chamber D in
close optical relation with the flame F to be monitored and
controlled, and equipped with an ionization tube T sensitive to
ultraviolet radiation, polarization circuits, discharge control,
and transmission of the pulse signals;
A line B connected to the detecting head, by means of two or more
wires, to supply power to the head and to transmit the signals over
a distance;
An electronic control station C placed at a proper distance,
connected to line B, and having apparatus which performs the
following functions:
a. an electric power supply to supply power to the head at proper
voltage and power levels;
b. means for receiving and converting the received pulse signals to
develop a quantitative indication thereof, on local or remote
display instruments I;
c. means for receiving the pulse signals and, on the basis of their
intensity and sensitivity levels predetermined by calibration,
causing the flame relay to be energized or de-energized, for the
purpose of actuating the safety devices of the burner in case of
absence of flame.
This latter function (c) is by far the most critical for the
purposes of the safety of the entire system, and, therefore, a
special objective of the present invention, which consists of a new
and improved type of control station, which combines with excellent
performance the advantage of being fully fail-safe.
This characteristic is completely independent of whether or not
there are devices and/or circuits employed for the periodic
checking of the tube operating characteristics, which, therefore,
can be done at times and in ways most suitable for the particular
case.
The invention is based on the following consideration:
For a complex electronic apparatus consisting of a series of stages
to be fail-safe, it is sufficient that the following two conditions
are met simultaneously:
a. each individual state must be fail-safe, in the above sense;
b. the series must be conceived so that non-occurrence of the
characteristic signal in any one stage prevents the output of the
characteristic signals in all subsequent stages.
To obtain the degree of safety required in flame detector stations,
an apparatus has been developed which meets these requirements and
which in its preferred realization operates according to the block
diagram of FIG. 2.
Independently of the methods of transmission of the pulse signals
to the control station, each stage, represented by a "block box,"
is made to operate dynamically, so that each component continuously
and periodically runs through all points of its operating
characteristic.
For this purpose, where necessary, periodic test signals of a
sufficiently high frequency (for example, 1 KHz) are introduced,
and the output relay can be energized only if the entire apparatus
correctly responds to the test signals.
In the diagram of FIG. 2, the oscillator stage O furnishes the test
signals, which may be rectangular wave signals of a given frequency
(for example 1 KHz) or other signals of properly defined
characteristics.
To prescind from the symbols used in the diagram, the nature of
function of each stage is as follows:
Stage 1 (preferably a transformer) receives the signals from the
line and transfers only the pulse signals, while adapting the
impedance of the line to the input impedance of the control
station.
Stage 2 (preferably a rectifier and pulse shaper) gives to the
signals a specific form and level.
Stage 3 (preferably a capacitor) utilizes the alternation of levels
to transfer energy to the following stages.
Stage 4 (preferably an adjustable potentiometer) calibrates the
sensitivity of the system, suitably proportioning the transfer of
energy.
Stage 5 (preferably a capacitor) stores the energy received from
the signals, giving at the output a voltage level corresponding to
the integral mean.
Stage 6 (preferably a controlled switch), by a special test signal,
samples the voltage at the input.
Stage 7 (preferably a trigger circit), generates a digital output
signal whenever in a sampled signal it exceeds a certain threshold
level chosen on the basis of the required maximum sensitivity.
Stage 8 (preferably a capacitor) utilizes this alternation of
levels to restore the level of energy stored by it and from which
it furnishes a continuous signal.
Stage 9 (preferably a controlled switch), by means of the test
signal, samples the input signal.
Stage 10 amplifies the available signal power.
Stage 11 (preferably a transformer) lastly transfers to the final
flame relay K the signals resulting from the chain in normal
operation, constituting a barrier for those signals which may
derive from breakdown or non-function of the preceding stages.
Other purposes, characteristics and advantages of the invention
will become evident from the following description, with reference
to the diagram shown in FIG. 3, which shows a preferred realization
of a complete control station for flame detection constructed
according to the invention.
To the terminals a and b is applied the feed voltage of the
apparatus, of 24 V d.c.
The voltage is stabilized by the transistor Q1 to a value of +15 V.
The transformer T1, with the transistor Q2 and Q3, operates as an
inverter self-oscillating at a frequency of about 1 KHz, which
furnishes the negative voltage of -15 V, the periodical test
signals of rectangular wave fluctuating between +1.5 V and -1.5 V
at 1 KHz and also furnishes via the diode 17, the capacitor 16 and
the protection resistor 13, to the terminals c and d, a continuous
voltage of 700 V, which is coupled to the detector head over a line
to provide the ionization tube the necessary voltage of the proper
polarity.
Using the wire coupled to terminal d as a common wire, the pulse
signals generated by the discharge of the tube due to the
ultraviolet rays reach the control station over a third wire ending
at the terminal e.
The pulse transformer T2 which corresponds to stage 1 in FIG. 2
transfers the signals separating the continuous voltage levels, and
brings about the best impedance adaptation for all alternate
components which constitute the signal. The diode Bridge 18, the
capacitor 22 and the amplifier formed by Q4 constitute the stage
which full wave rectifies and shapes the input to give to the
pulses a specific form (stage 2 in FIG. 2), as on the collector of
Q4 the voltage switches from 15 to 0 V and then goes up again.
The capacitor 26 with the diodes 27 and 28 (stage 3 in FIG. 2)
carries out a fail-safe coupling and stores energy while Q4 is
turned off (charging through 27), and then transferring a negative
voltage to the next stage when Q4 becomes saturated. The adjustable
potentiometers 30-31 (stage 4 in FIG. 2), properly limiting the
current flow, permit calibrating the sensitivity from the outside
of the control station to obtain the best discrimination between
near-by flames.
The sensitivity of the control station may be changed by closing an
external contact 19 across the terminals h and i. This causes the
switching of contact S1 by coupling terminal 71 to 0 V (terminal 72
being coupled to -15 V). A visually observable light signal is
generated by means of the luminescent (i.e. light emitting) diode
L.
The capacitor 32, in the presence of flame signals (stage 5 in FIG.
2) establishes a voltage at terminal 32a which is negative relative
to ground bus 0 V, the mean value of which, as the frequency of the
pulses at the input increases, has an approximately logarithmic
response owing to the Zener diode 33 and the resistor 34.
An ideal response curve is thereby obtained in that it permits
maintaining the discrimination properties of the apparatus at an
optimum level within an extremely wide range of radiation
intensities, as they occur in practical cases, avoiding the
phenomena of uncertainty of measurement or saturation. The voltage
present on the capacitor 32 is applied to the following stages
intermittently, by effect of the transistor Q5 (stage 6 in FIG. 2)
piloted (i.e. alternately operated between conduction and
non-conduction) by the test signal coupled thereto by transformer
T1.
The next stage is a Schmitt type threshold discriminator (stage 7
in FIG. 2), comprising transistors Q6 and Q7, which, in turn,
detects the presence of the flame with fail-safe reliability as it
must continuously switch by effect of the flame signal.
In the preferred realization, the threshold of the Schmitt
discriminator is put at 2 V. That value is not determining for the
purposes of safety, but only to specify the sensitivity of the
trigger circuit.
Capacitor 40, in the same manner as capacitor 26, serves to make a
fail-safe connection. In particular the energy accumulated by
capacitor 40 in the switching cycles is sufficient to maintain in
operation the downstream circuits and hence to keep energized the
flame relay K for a pre-established time, after the non-occurrence
(i.e. termination) of the flame signals.
Resistors 43 and 44 serve to adjustably determine the
de-energization delay time of relay K, to a greater or smaller
elapsed interval according to the ohmic values of the resistors and
the position of switch G. (The capacitor 40 in combination with the
diodes 41 and 42 with either resistor 43 or 44 corresponds to stage
8 in FIG. 2).
Normally the de-energization time is 1 second. The transistor Q8
(stage 9 in FIG. 2) acts in a manner analogous to transistor Q5, to
make the transfer of the energy accumulated in capacitor 40 to the
following stages intermittent in nature.
The transistors Q9 and Q10 and the resistors 46, 47, 48 are the
components of the power amplifier stage (stage 10 in FIG. 2) which,
like the others, must operate dynamically. The two input terminals
of this stage are formed by the terminals 46a and 46b of resistor
46, while the two output terminals are represented by the collector
73 of Q10 and by the +15 V line coupled to terminal 74. For this
stage, the cyclic dynamic operation is achieved, for example, as
follows:
In this stage, the test signal coincides with the useful input
signal. This signal is periodically variable, as the preceding
stage (stage 9 in FIG. 2) furnishes a periodically sampled useful
signal. In every period of its cyclic dynamic operation, the stage
(10 in FIG. 2) can assume two extreme operating points,
corresponding to the simultaneous non-conduction or saturation of
the two transistors Q9, Q10. With the cyclic dynamic operation of
the stage, which occurs between said two extreme points, also each
component of the stage (Q9, Q10, 46, 47, 48) periodically and
continuously runs through all points of its operating
characteristic.
Lastly the transformer T3 with the diodes 49 and 50 (stage 11 in
FIG. 2) provides for the energization of relay K, in an absolutely
fail-safe manner.
A separate circuit, formed essentially by the operational amplifier
70, serves to provide a quantitative indication of the flame
intensity on a measuring instrument M1 included in the apparatus,
and, if further desired, on a remote instrument M2, assuming as
zero the minimum value which is sufficient to energize the flame
relay, regardless of the calibration sensitivity of the
apparatus.
The input signal at the amplifier 70 is obtained from the collector
of Q5 by means of the resistors 57, 58 and 59 and is filtered by
the capacitor 56. It follows that no energization of relay K can
result from any failure of the amplifier A.
While a preferred form of realization of the invention has been
illustrated and described, various modifications thereof will be
evident to the specialists, and it is therefore understood that the
invention is not limited to the form of realization set forth or to
the details thereof, and that it includes the departures therefrom
in the spirit and scope of the invention derivable from the
description, drawings and claims.
* * * * *