Note: Descriptions are shown in the official language in which they were submitted.
CA 02380397 2002-O1-21
WO 01/06808 PCT/US00/19898
-1-
METHOD AND APPARATUS FOR SUPERVISING AN AUDIO
CIRCUIT WITH CONTINUOUS AUDIO
This application claims the benefit of U.S. Provisional Application
No. 60/144,718 filed on July 20, 1999, which is herein incorporated by
reference.
The present invention relates to a method and apparatus for
monitoring an electrical circuit. More particularly, the invention relates
to a method and apparatus for monitoring an audio circuit while the audio
circuit is simultaneously generating a continuous audio signal.
BACKGROUND OF THE DISCLOSURE
Commercial facilities, such as manufacturing plants, office
buildings and the like, often have comprehensive and sophisticated facility
alarm system. Such facility alarm system may include a fire alarm
system, a paging system, a security system and the like. Since safety is a
paramount goal, stringent requirements or governmental codes must be
satisfied in the deployment of such systems.
Specifically, fire alarm system is traditionally deployed separately
from that of a voice announcement or paging system. The rationale for
such duplicity is the high priority that is placed with the fire alarm
system, where its proper operation is paramount. To ensure that the fire
alarm system is extremely reliable, regulations often prohibit the sharing
of fire alarm system components for other functions, such as paging,
thereby requiring duplication and increasing the cost of deployment of
such systems.
However, as reliability of fire alarm systems have been
demonstrated over the years, regulations have been relaxed and there is a
trend where fire alarm system components can be shared with other
systems, provided that fire alerting functions are given priority over that
of other secondary functions such as paging. The ability to share system
components is desirable and will significantly reduce the cost of deploying
such systems. For example, the speakers that are deployed for
broadcasting fire alarms can now be adapted to provide voice
announcement functions.
CA 02380397 2002-O1-21
WO 01/06808 PCT/US00/19898
-2-
However, fire alarm system often requires constant supervision of
its alert components to ensure that they are in proper operating order.
For example, a fire alarm system often polls its alert components and/or
wiring in regular time periods, e.g., every 90-200 seconds, to verify that
there is no short circuit, open circuit or fault at any of its alert
components. This creates an unique problem, if the speakers of the fire
alarm system also serve voice announcement functions. Namely, a voice
announcement may be interrupted every 90 seconds when the fire alarm
system is performing its supervising or monitoring functions. In fact, if
the speakers of the fire alarm system are used to provide continuous
broadcast, e.g., providing background music in an elevator, then the
continuous broadcast will be interrupted every 90 seconds. Such
interruptions are simply impractical.
Thus, there is a need for an apparatus and method for monitoring
an audio circuit while the audio circuit is simultaneously generating an
audio signal.
SUMMARY OF INVENTION
In one embodiment of the present invention, an apparatus and
method for monitoring an audio circuit while the audio circuit is
simultaneously generating an audio signal is disclosed. Specifically, an
AC audio signal and DC current source supervision signal are
superimposed over a speaker circuit.
In operation, an AC current source (audio signal) is passed through
a first DC filter to the field wiring, whereas a DC current source flows
through a first AC filter to the field wiring. These signals are
superimposed at the junction where the first DC filter and the first AC
filter are connected. The field wiring may consist of supervised speakers
and an end of line resistor (EOLR). Second DC filter at each speaker
blocks DC current flow, when the AC signal is played through the
speakers. This unique configuration provides the ability to monitor an
audio circuit for fault conditions while the audio circuit is simultaneously
generating an audio signal. The detected fault conditions may include
open circuit and short circuit.
CA 02380397 2002-O1-21
WO 01/06808 PCT/US00/19898
-3-
BRIEF DESCRIPTION OF THE DRAWINGS
The teachings of the present invention can be readily understood by
considering the following detailed description in conjunction with the
accompanying drawings, in which:
FIG. 1 depicts a block diagram of a monitoring apparatus of the
present invention;
FIG. 2 depicts a schematic block diagram of the monitoring
apparatus of FIG. 1; and
FIG. 3 depicts an alternate schematic block diagram of the
monitoring apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
In a typical audio system, the wiring of the system is supervised for
an end of line device in the normal (stand-by) state. However, when the
audio signal is played, the supervision function stops. Such interruption
in the supervision function may not meet fire alarm system requirements.
Conversely, if supervision function is consistently maintained, then the
audio signal may have to be interrupted during broadcast, which is
undesirable in practice.
FIG. 1 depicts a block diagram of a monitoring apparatus 100 of the
present invention. This circuit allows simultaneous supervision of fault
conditions, i.e., supervision of the end of line device, and the playing of an
audio signal through one or more speakers. The monitoring apparatus
100 comprises a monitoring circuit 110 (e.g., a DC current source and
detect circuit), an audio amplifier 120, an AC (alternate current) filter 130,
DC (direct current) filters 140 and 150$_n, an end of line device 160 and one
or more audible devices 170$_n (e.g., speakers).
In operation, an audio signal (e.g., an AC signal) and a supervision
signal (e.g., a DC current source supervision signal) are superimposed
over a speaker circuit. The audio signal is optionally received and
amplified by the audio power amplifier 120, which is then passed to the
DC filter 140 (first DC filter). The DC current through the audio power
amplifier is blocked by the DC filter 140.
Similarly, the supervision signal is generated and monitored by the
monitoring circuit 110, which is then passed to the AC filter 130 (first AC
filter). The AC current through the monitoring circuit 110 is blocked by
CA 02380397 2002-O1-21
WO 01/06808 PCT/US00/19898
-4-
the AC filter 130. Both, the audio signal and the supervision signal are
superimposed at junction 145.
DC filters 150$_n (second DC filter) are deployed with corresponding
audible devices, i.e., speakers 170a_n, to block DC currents. An end of the
line device 160 is deployed to assist in the wire monitoring function.
FIG. 2 depicts a schematic block diagram of the monitoring
apparatus 100 of FIG. 1. Audio signal from the power amplifier 120 is an
AC current source (audio signal) coupled through the transformer (T1) and
through the DC filter 140 (C1) to the field wiring. The power amplifier
120, transformer (T1), and DC filter 140 (C1) are coupled in series. DC
current through the amplifier is blocked by C1. It should be noted that
the transformer T1 is optional depending on the amplifier design. For
example, the output of the amplifier can be capacitively coupled using the
same ground reference as that of the circuit, e.g., changing the value of
C1.
The monitoring circuit 110 comprises two comparators (U1 and U2)
210 and 212, a resistor (R1) 214 and a capacitor (C2) 216. In operation,
DC flows through resistor R1 and inductor L1 to the field wiring. Thus,
the supervision signal and the audio signal are superimposed at the
junction 145, where inductor L1 and capacitor C1 are connected. The field
wiring consists of one or more supervised speakers 170a_n and an end of
line resistor (EOLR). The DC filters 1508_n (i.e., bypass capacitors (Cs)) at
each speaker block DC current flow as the AC signal is played through the
speakers.
In one embodiment, R1 and EOLR are of equal value and form a
voltage divider (the resistance if the inductor is small compared to Rl).
The two comparators form a window of accepted resistance for EOLR. For
example, an open circuit in the speaker circuit wiring or missing EOLR
will cause V sense to go above 2/3 VDC and cause comparator U1's output
to go low, thereby indicating an open circuit condition. Conversely, a short
circuit in the speaker wiring will cause V sense to go below 1/3 VDC and
cause comparator U2's output to go low, thereby indicating a short circuit
condition.
Table 1 provides actual values for various components of FIG. 2 in
one embodiment. It should be noted that the values of these components
can be adapted and modified as required in a particular application.
CA 02380397 2002-O1-21
WO 01/06808 PCT/US00/19898
-5-
Component Values
C 1 470uf
C2 100uf
C s l0uf
R1 lOk
EOLR lOk
L1 1 H
Table 1
FIG. 3 depicts an alternate schematic block diagram of the
monitoring apparatus 100 of FIG. 1. Specifically, the alternate schematic
block diagram of FIG. 3 is identical to that of FIG. 2 with the exception of
an additional RC (resistor-capacitor) circuit (second AC filter) serving as
an additional AC filter. Resistor (R2) 320 and capacitor (C3) 310 are
placed at the input to smooth out any AC transient signal. The additional
AC filter may be useful where the size of the inductor L1 is reduced for
different application to ensure AC filtering.
Table 2 provides actual values for various components of FIG. 3 in
one embodiment. It should be noted that the values of these components
can be adapted and modified as required in a particular application.
Component Values
C 1 220uf
C 2 l0uf
C 3 1uf
C s l0uf
R1 lOk
R2 100k
EOLR lOk
L1 1.4 MH
Table 2
CA 02380397 2002-O1-21
WO 01/06808 PCT/US00/19898
-6
Although the present invention is illustrated as being deployed in
part or in whole within a fire panel, it should be noted that the present
invention is not so limited. Namely, the present invention can be
implemented as a separate module disposed between the fire panel and
the speakers.
It should be noted that although the present invention is described
using various resistor, capacitor and inductor combinations to implement
various filters, those skilled in the art can implement these filters in view
of the present disclosure using other components or combinations to effect
similar results. Thus, although various embodiments that incorporate the
teachings of the present invention have been shown and described in
detail herein, those skilled in the art can readily devise many other varied
embodiments that still incorporate these teachings.
