Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR DETECTING ARCS
AND CONTROLLING SUPPLY OF ELECTRICAL POWER
The present invention relates generally to detecting and controlling
electrical
arcs, and specifically to detecting and controlling electrical arcs occurring
in a cleaning
cell of an electronic air cleaner.
Electronic air cleaners are currently available that filter particles from the
air by
charging the: particles so that they have an electrostatic charge, and then
passing the
charged particles between high voltage plates. The plates have an electric
potential
between them, and the charged particles are attracted to and collected on the
plate that
has a polarity opposite to the charge on the particles. Thus, the particles
are removed
from the air. For example, if the particles are given a positive charge and
then passed
between two plates that have an electric potential between them, the particles
will be
attracted to the plate that is connected to the lesser voltage.
Arcing can occur when accumulated debris narrows an effective gap between the
high voltage: plates. Since the electric potential between the plates is
typically large, for
example at lleast several thousand volts ) when the effective gap becomes
small an arc
will occur along a path across the gap. Current flows between the plates along
the path,
generating a high rate of change in current flow, i. e. , a large dI/dt. The
large dIldt
creates a burst of electromagnetic noise that often has frequency components
in the 300
kHz range, a short duration on the order of several microseconds or less, and
a
relatively high local intensity in comparison to other electromagnetic signal
sources
when measured near the arc. This electromagnetic noise burst often interferes
with the
electronics within the air cleaner as well as with other electrical devices
near the air
cleaner, such as television sets, radios, and personal computers. The burst of
electromagnetic noise resulting from the arcing affects digital circuits and
microprocessors, because the conductive components in the circuit and
microprocessors
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act as antennae that receive the noise signal and generate erroneous pulses.
These
erroneous pulses cause the digital circuits and microprocessors to reset or
malfunction
in unpredictable ways.
In addition, sound created by arcing in an electronic air cleaner can be
especially
annoying to a user because arcs typically occur in rapid succession. The arc
ionizes the
air in the inunediate vicinity of arc's path, which increases the conductivity
of the path
and therefore the likelihood that subsequent arcs will occur. Where the arcing
is caused
by large debris trapped between cell plates in the air cleaner, arcing can
continue
indefinitely until the debris either burns away or falls from between the cell
plates, or
until a user disconnects the air cleaner's power source.
Arcing can also be undesirable for other reasons. For example, arcing
generates
ozone which can be harmful. Arcing can also overload the air cleaner power
supply as
well as consume unnecessary amounts of electrical power.
The invention solves the foregoing problems and provides additional
advantages,
by providing a method and apparatus for detecting arcs and controlling a power
supply
that powers the arcs . In accordance with an exemplary embodiment of the
invention, an
arc detection circuit and a power supply control circuit are provided. The arc
detection
circuit includes an antenna, a filter, and a single shot timer. The antenna
receives a
portion of tlhe electromagnetic noise generated by an arc. The antenna is
connected to
the filter, which filters out received signals not generated by the arc. An
output of the
filter is provided to the single shot timer, and an output of the single shot
timer is
provided to the relay control circuit. When activated, the power supply
control circuit
stops the arcing by disconnecting the power supply. When the timer receives a
signal
from the antenna via the filter that corresponds to an arc, the timer
generates a pulse
that endures for a predetermined amount of time. The pulse activates the power
supply
control circuit, which disconnects the power supply until the timer ceases to
generate
the pulse. Thus, arcing can be reduced.
According to another exemplary embodiment, a microprocessor can be provided
between the: single shot timer and the power supply control circuit, to allow
for more
sophisticated control of the power supply in response to detected arcing. For
example,
the microprocessor can be configured to vary the time during which the power
supply is
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disconnected, depending on how often the arcs occur. The microprocessor can
also be
configured to initiate other actions when arcing conditions exceed
predetermined
parameters. For example, when arcing occurs the microprocessor can be
configured to
generate a warning signal to alert a user, andlor initiate an automatic wash
cycle to
flush away debris that has collected in the region where the arcs are
occurring.
According to another exemplary embodiment, an additional filter is provided to
prevent transients in a power source supplying the arc detection circuit from
causing the
arc detection circuit to erroneously detect an arc.
Additional features and advantages of the invention will become apparent from
the following description of the preferred embodiments, taken in conjunction
with the
accompanying drawings. The accompanying drawings illustrate, by way of
example,
the principlfa of the invention. Like elements are designated with like
reference
numerals. Like elements in the drawings have been designated by like reference
numerals.
FIG. 1 is a block circuit diagram of an arc detection circuit and a power
supply
control circuit according to a first embodiment of the invention.
FIG.. 2 is a block circuit diagram of a filter for filtering power supplied to
the
arc detection circuit.
FIG. 3 is a circuit diagram of a conventional low-pass filter typically used
on an
inputloutput line of an integrated circuit.
FIG. 4 is a block circuit diagram showing a microprocessor connected between
an output oiF either an antenna or a single shot timer, and an input of a
power supply
control circuit.
FIG. 5 illustrates an exemplary antenna configuration consistent with the
invention.
FIG. 1 shows a block circuit diagram of a first preferred embodiment of the
invention for use in an electric air cleaner having a high-voltage power
supply) which
includes an arc detection circuit 100 and a power supply control circuit 101.
The arc
detection circuit 100 includes an antenna 102 connected to a single shot timer
112 via a
filter formed by a filter resistor 106 and a filter capacitor 108. The power
supply
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control circuit 10l includes an input resistor 118 connected between an output
line 116
from the single shot timer 112, a transistor l20) a diode 122, a solenoid coil
124 and a
normally-closed solenoid switch 126.
The voltage Vdd shown in FIG. 1 is the voltage provided by a power supply for
the air cleaner, and is always present during normal operation of the air
cleaner. The
voltage Vtt is a switchable output of the power supply, and can be turned off
or on by
the power supply control circuit 101. The voltage Vcc is a voltage that is
derived from
the voltage Vdd and used to power the solenoid coil 124 and the filter formed
by the
filter resistor 106 and the filter capacitor 108. The voltage Vcc is also used
to power
integrated circuits (IC's) within the air cleaner and provide a logic voltage
level source
for any digital circuits incorporated in the air cleaner.
In operation, the antenna l02 receives an electromagnetic noise signal
produced
by an arc. The signal passes through the filter formed by the resistor 106 and
the
capacitor 108 to the input line 114 of the single shot timer 112. In response
to the
signal, the single shot timer 112 outputs a pulse on the output line 116 for a
predetermined amount of time. The pulse on the output line 116 turns the
transistor 120
on so that current flows through the transistor 120 and the solenoid coil 124,
thus
causing the solenoid coil l24 to operate as an electromagnet that opens the
solenoid
switch 126 and disconnects the power supply line 128. When the predetermined
amount
of time expires, the single shot timer 112 stops outputting the pulse, the
transistor 120
turns off, anal the solenoid switch 126 closes to reconnect the power supply
line 128.
The diode 1:Z2 provides a path for receiving current produced when the
magnetic field
generated by the solenoid coil collapses after the transistor 120 is turned
off.
The filter resistor 106 and the filter capacitor 108 together form a filter
for
filtering out transients not caused by an arc. The filter resistor 106 is
selected so that its
resistance is large enough to prevent the single shot timer 112 from being
triggered by
normal transients caused by the system turning on or by electromagnetic
signals from
other source's such radio stations, cordless phones, and so forth. However,
the resistor
106 is also selected so that its resistance is small enough to allow
electromagnetic noise
due to arcing to be reliably detected. For example, the filter resistor 106
can be chosen
to have a value near l00 kilohms. The filter capacitor 108 offers additional
immunity to
undesired transients, and is typically small in value. For example, the filter
capacitor
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108 can be selected to have a capacitance near 0.02 microfarads. However, the
filter
capacitor 108 and the filter resistor l06 can have other values consistent
with particular
applications of the invention. In many cases, the filter capacitor 108 can be
omitted.
This is because the conductive paths of the arc detection circuit 100,
particularly when
implemented on a printed circuit board, have a sufficient amount of inherent
capacitance to form an effective filter with the filter resistor l06.
According to an embodiment of the invention, the single shot timer 112 and the
resistance value of the resistor l I8 are chosen so that the pulse output from
the single
shot timer 'l12 has sufficient amplitude to drive the transistor 120 into
saturation. The
predetermined amount of time that the single shot timer outputs a pulse can be
chosen
according to specific requirements for a particular application. For example,
in one
embodiment the predetermined amount of time can be between 4 and 10 seconds,
to
allow the arc to fully subside and the ionized path across which the arc
passed to fully
dissipate.
The. single shot timer I 12 can be implemented using an IC such as a 555
timer.
Other circuits or IC's capable of performing the same function can
alternatively be
used, in accordance with single shot timer designs and operating principles
well known
in the electrical arts.
A power line filter such as that shown in FIG. 2 can also be provided, to
prevent
non-arc related transients that occur on a power line (not shown) supplying
the arc
detection c ircuit 100 from adversely affecting performance of the arc
detection circuit.
As shown in FIG. 2, resistor 206 and capacitor 204 together form a low-pass
filter to
suppress transients. A zener diode 202 acts as a voltage clamp to further
limit
transients. The power line filter shown in FIG. 2 also doubles as a voltage
regulator for
providing the voltage Vcc given the source voltage Vdd.
Depending on the IC or circuit chosen to implement the single shot timer 112,
other inputs (not shown) to the single shot timer 112 besides the input line I
14 might
require an input/output (I/O) line filter such as that shown in FIG. 3, to
ensure proper
operation of the single shot timer I12. The other inputs might be, for
example, inputs
that configure the single shot timer 112 and that should be free of transients
from arcs
or other sources. As shown in FIG. 3, a resistor 304 is connected between the
input line
and the IC.', and a capacitor 306 connects the junction between the resistor
304 and the
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IC to ground. Other IC's or circuits used in the arc detection circuit I00
might also
require an a/O line filter such as that shown in FIG. 3, for similar reasons.
In another embodiment of the invention, a microprocessor 402 is connected
between the single shot timer 112 and the output line 116 as shown in FIG. 4.
The
microprocE;ssor 402 allows the power supply to the arc source to be controlled
with
greater sophistication. For example, the microprocessor can vary the time
during which
the power supply is discontlected, depending on how often the arcs occur. For
example,
the discomaect time can be based on how much time elapsed between the most
recent
two arcs) or on how many arcs occur within a predetermined period of time. The
microprocessor can also be configured to initiate other actions when arcing
conditions
exceed predetermined parameters. For example, when arcing occurs the
microprocessor
402 can be configured to generate a warning signal to alert a user, and/or
initiate an
automatic wash cycle to flush away debris that has collected in the region
where the
arcs are occurring. The microprocessor 402 can also be used to create a record
of arc
occurrences over a period of time. This record can be used, for example, to
schedule or
evaluate periodic maintenance of the electric air filter) or to troubleshoot
the filter when
performing repairs.
Depending on the configuration of the filter formed by the resistor 106 and
the
capacitor 108 and on how the input of the microprocessor 402 is internally
buffered and
configured, the microprocessor 402 can replace instead of augment the single
shot timer
112. In addition, a signal output from the antenna 102 could be otherwise
conditioned
for input to the microprocessor, in accordance with techniques well known in
the
electrical arts. For example) the signal could be input to a threshold device
which would
output a digital signal while the input signal from the antenna remained above
a
threshold.
The antenna 102 can be configured in different ways. According to an
embodiment of the invention, the antenna 102 is configured in a shape 502 as
shown in
FIG. 5) so that portions of the antenna 102 lie in each of three mutually
perpendicular
planes. For example, the antenna can be formed using conductive traces along
two axes
of a printed circuit board (PCB), with an additional segment of the antenna
looping
away from and then back toward the PCB in a direction substantially
perpendicular to
the PCB. The Iength of the loop and the lengths of the conductive traces on
the PCB can
CA 02228724 1998-02-04
affect the sensitivity of the antenna, and thus can be chosen to obtain an
antenna with a
desired sensitivity that matches the filter formed by the filter resistor 106
and the filter
capacitor 108. The antenna 102 can also be placed at different locations in
the electric
air filter relative to the arc source, based for example on factors such as
available space
within the air filter given a specific physical configuration of air filter
components, and
relative strength of arc-sourced electromagnetic signals at different
locations within the
available space. In addition, the antenna can also be configured differently,
for example
in a toroid.
In summary, the disclosed embodiments of the invention variously provide
multiple advantages, especially when implemented in an electronic air cleaner
that uses
a high voltage power supply to filter particles out of the air. First, noise
generated by
arcing is linuted to a short duration tapping sound instead of a rapid
succession of pops
and crackles, because the power supply for the arcs is disconnected when an
arc is
detected. Second, subsequent arcs are prevented when an arc across debris
trapped
between arcing surfaces is detected, because disconnecting the power supplying
the arc
allows the debris to fall out from between the arcing surfaces within a
cleaning cell, or
to pass through the cleaning cell with an air flow. Third, a microprocessor
included in
the arc detection and power supply control circuits allows arcing to be
monitored and
power to beg controlled in sophisticated ways that optimize performance and
user-
friendliness of the system. Fourth, arc-generated interference with other
devices such as
televisions ;end radios is reduced. Additional advantages will be apparent to
those skilled
in the art.
The principles, preferred embodiments and modes of operation of the present
invention have been described in the foregoing specification. However, the
invention
which is intended to be protected is not to be construed as limited to the
particular
embodiments disclosed. Further, the embodiments described herein are to be
regarded
as illustrative rather than restrictive. The invention could be used with
devices other
than electric air filters to control arcing, for example with any device that
generates
undesired arcs that can be interrupted or controlled if detected. Variations
and changes
may be made by others, and equivalents employed, without departing from the
spirit of
the present invention. Accordingly, it is expressly intended that a11 such
variations,
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changes and equivalents which fall within the spirit and scope of the present
invention
as defined in. the claims be embraced thereby.
