U.S. patent number 3,710,373 [Application Number 05/036,368] was granted by the patent office on 1973-01-09 for signal discriminating system.
Invention is credited to Fumio Aoki, Shigeru Kawano, Hiroshi Oishi, Kozo Ozaki, Seizi Watanabe.
United States Patent |
3,710,373 |
Watanabe , et al. |
January 9, 1973 |
SIGNAL DISCRIMINATING SYSTEM
Abstract
An improvement in a signal discriminating system used in a
monitoring and control system for a low voltage commercial power
distribution line, in which a high frequency signal is superimposed
on the power current of 50 or 60 Hz, as a communication medium
between a monitoring spot and consumers connected to the
distribution line; the improvement resides in that in the
centralized reading of the meters of respective consumers, the
monitoring channel is time-divided or frequency-divided in order to
provide a reference signal level peculiar to each consumer.
Inventors: |
Watanabe; Seizi (Midori-ku,
Yokohama, JA), Ozaki; Kozo (Minato-ku, Tokyo,
JA), Oishi; Hiroshi (Kohoku-ku, Yokohama,
JA), Aoki; Fumio (Minami-ku, Yokohama, JA),
Kawano; Shigeru (Adachi-ku, Tokyo, JA) |
Family
ID: |
26377899 |
Appl.
No.: |
05/036,368 |
Filed: |
May 11, 1970 |
Foreign Application Priority Data
|
|
|
|
|
May 14, 1969 [JA] |
|
|
44/38630 |
May 14, 1969 [JA] |
|
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44/38633 |
|
Current U.S.
Class: |
340/870.02;
340/13.2; 307/3 |
Current CPC
Class: |
H02J
13/00009 (20200101); Y04S 40/121 (20130101); Y02E
60/7815 (20130101); Y02E 60/00 (20130101); Y02B
90/20 (20130101) |
Current International
Class: |
H02J
13/00 (20060101); G08c 015/10 () |
Field of
Search: |
;340/177CA,188.5CH,183,310 ;307/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Habecker; Thomas B.
Claims
What we claim is:
1. Apparatus for remotely monitering at least one consumer load
sensing means connected to low voltage commercial power
distribution lines for measuring a load connected across said
distribution lines, comprising:
injecting means for injecting a high frequency signal having at
least one frequency component into said distribution lines, wherein
the portion of said high frequency signal alloted to a given
consumer has a reference signal portion and a measuring signal
portion;
flow path circuit means providing a signal flow path for said
reference signal portion;
switching means for selectively connecting said flow path circuit
means across said distribution lines in parallel with said
load;
load sensing means operative in response to the state of said load
to create a flow path for said measuring signal portion through one
of said flow path circuit means and said load, depending upon the
state of said load;
detector means for detecting said reference signal portion and said
measuring signal portion; and
comparing means for comparing the levels of the detected reference
and measuring signal portions to obtain information relating to the
state of said load.
2. Apparatus as defined in claim 1, wherein said high frequency
signal comprises one frequency component; and said flow path
circuit means comprises a series resonant circuit tuned to said
high frequency signal.
3. Apparatus as defined in claim 1, wherein said high frequency
signal comprises first and second frequency components to be
concurrently injected serving as said reference signal portion and
said measuring signal portion, respectively; and said flow path
circuit means comprises first and second series resonant circuit
means tuned to said first and second frequency components,
respectively.
4. A system as defined in claim 1, wherein said load sensing means
comprises a watt-hour meter, and said means operative in response
to the state of said device comprises a switch contact which
operates once for each time said watt-hour meter reads a
predetermined amount of power consumption in said load.
5. Apparatus as defined in claim 1, wherein: said high frequency
signal comprises:
a starting signal portion for putting a second load into a
controllable condition,
first and second command signal portions for controlling said
second load,
a second reference signal portion, and
a second measuring signal portion; and
the apparatus further comprises:
starting means responsive to said starting signal portion of said
high frequency signal for initiating the control operation of said
second load;
first control circuit means responsive to said first command signal
portion of said high frequency signal for generating a first
control signal;
second control circuit means responsive to said second command
signal portion of said high frequency signal for generating a
second control signal;
further switching means for selectively connecting said first and
second control circuit means in parallel with said starting means;
and
relay means connected to the outputs of said first and second
control circuit means for connecting said second load and said flow
path circuit means to said distribution lines, wherein said relay
means connects said second load and said flow path circuit means to
said distribution lines in response to said first control signal
and disconnects said second load and said flow path circuit means
from said distribution lines in response to said second control
signal and wherein said flow path circuit means provides a signal
flow path for said second reference signal portion;
wherein said detecting means and said comparing means respectively
detect and compare said second reference and measuring signal
portions in the same manner as the first reference and measuring
signal portions.
Description
This invention relates to a signal discriminating method and system
used in a monitoring and control system for the low voltage
commercial power distribution line, in which a high frequency
signal superimposed on the power current serves as a communication
medium between a monitoring spot and consumers, the function of the
system including the automatic and centralized reading of the
consumers' watt-hour meters, the remote control of the consumers'
loads, and other metering for surveillance of the distribution
system.
In the modern commercial power distribution system, high frequency
signals are used for the purpose of control and monitoring, the
signals being injected to the distribution lines in a superimposed
manner on the commercial current of 50 or 60 Hz. Usually, the
voltage level of such a signal at consumer's ends varies depending
on various causes including differences in the length of the
distribution lines connected to consumers, variation in the
injection level of the signals and differences or changes in the
loads of the consumers.
The main object of this invention is to provide an improved signal
discriminating method and system which allows the above-mentioned
reading of the consumer's meters to be effected in a stable and
reliable manner notwithstanding the above-mentioned variation of
the signal level.
Another object of this invention is to provide such a method and a
system also including functions of allowing the centralized control
of the consumer's loads and the confirmation of the results of the
control to be effected in a single monitoring cycle including the
periods for the above-mentioned reading of the consumers'
meters.
In order to achieve the above objects, this invention provides an
improvement in the signal discriminating method used in the
monitoring and control system having functions of injecting high
frequency signals to the distribution line at a monitoring spot,
detecting a predetermined degree of variation in the injected
signal due to a change in the channel of the signal and a function
provided at each consumer for changing the state of the signal flow
path depending on the condition which is the object of the
monitoring, said change in the state of the flow path being made
effective during predetermined periods allotted to the consumer;
the improvement residing in that a further function is provided at
each consumer to produce a reference state of the signal flow path
during said allotted period regardless of said change in the flow
path, and that said detection of the variation in the signal is
performed by comparing the levels of two signals resulting from
said two functions provided at the consumer.
The features and merits of this invention will be clarified by the
following description given in connection with embodiments of the
invention and in comparison with the prior art and further with
reference to the accompanying drawings, in which;
FIG. 1 is a block diagram of the conventional monitoring or
metering system for a power distribution line;
FIG. 2 is a diagram showing waveforms found in the system shown in
FIG. 1;
FIG. 3 is a block diagram of a monitoring system including an
embodiment of this invention;
FIG. 4 is a diagram illustrating waveforms found in the system
shown in FIG. 3;
FIG. 5 is a block diagram of an essential part of the system shown
in FIG. 3;
FIG. 6 shows waveforms for explaining the operation of the circuit
shown in FIG. 5;
FIGS. 7 and 9 are block diagrams relating to other embodiments of
this invention; and
FIGS. 8 and 10 show waveforms observed at essential points in the
systems shown in FIGS. 7 and 9.
First, the conventional system will be described with reference to
FIGS. 1 and 2.
In FIG. 1, reference numeral 1 designates a signal injection
terminal; 2 a signal injector (illustrated as a current injection);
3 a series resonant circuit tuned to the frequency of the injected
signal; 4 a synchronous motor; 5 an auxiliary circuit which
integrates the signal received through the resonant circuit 3 in
order to enhance the assuredness of the signal and then actuates a
relay incorporated therein to start the synchronous motor 4; and
numeral 6 designates another series resonant circuit. Though
separate resonant circuits 3 and 6 are shown in the FIGURE for the
convenience of explanation, it is a usual practice to use a single
resonant circuit commonly for both circuits 3 and 6. Numeral 7
designates a switch operated with a timing peculiar to each
consumer as the synchronous motor 4 rotates; 8 another switch to
keep the resonant circuit 3 off the distribution line 14 after the
start of the motor 4 until the end of the intended metering cycle;
9 a further switch arranged to close and open for once each time
the consumer's watt-hour meter 10 reads another 1 kWH, for example;
11 a signal detector; 12 an output signal terminal; 13 the
consumer's load; and 15 another branch of the distribution line
extending from a pole transformer 16 to other consumers.
In FIG. 2, index (a) designates a waveform of the signal at the
signal injection terminal 1; (b) an example of waveform of the
signal as detected at the signal detector 11, showing the changes
in the signal level which reflect the states of watt-hour meters in
the respective consumers; and (c) to (h) timing pulses which allow
the distribution line to be used as the time-divided communication
channel, each pulse corresponding to the operation of the switch 7
shown in FIG. 7.
The operation of the system shown in FIG. 1 will be described
hereunder also with reference to FIG. 2. A radio-frequency or an
audio-frequency signal (a) shown in FIG. 2 is injected into the
distribution line 14 through the signal input terminal 1 and the
signal injector 2 to be superimposed on the power current. The
superimposed signal is led to the resonant circuit 3 through the
distribution line 14. The resonant circuit 3 detects the signal and
has the synchronous motor 4 started with the assistance of the
auxiliary circuit 5. The same operations concurrently occur at
other consumer devices connected to other branches 15 originating
from the same transformer 16. Thus, the synchronous motors at
respective consumers concurrently start to thereby close and open
the respective switches 7 according to predetermined timing
allotted to the consumers. When the switch 7 is in the closed
state, the resonant circuit 6 is ready to be connected across the
distribution line. The mutual relation in the timing of the
operation of the switch 7 at the respective consumers is shown in
FIG. 2 by waveforms (c) to (h) as mentioned previously. Whether the
resonant circuit 6 is actually connected across the distribution
line while the switch 7 is closed, or not, depends on the state of
the switch 9 which represents the state of the watt-hour meter and
which is connected in series with the switch 7. The switch 8 is
opened after the synchronous motor 4 is once started, so that the
resonant circuit 3 is kept off the distribution line 14 during the
allotted monitoring period. Therefore, the insertion of the
resonant circuit 6 to the line is the decisive factor to greatly
change the impedance of the signal channel or flow path. If the
resonant circuit 6 is connected across the line reflecting a start
of the watt-hour meter, the injected signal is led through the
resonant circuit 6 and undergoes only a small loss. If, on the
other hand, the resonant circuit 6 is removed from the line
reflecting the other state of the meter 10, the signal is led by
the route of the consumer's load and undergoes a heavy loss. Thus,
the state of the meter can be determined from the magnitude of the
signal detected in the signal detector 11.
In the above-described conventional system, however, the detected
signals for different periods allotted to respective consumers have
different signal levels even if a similar resonant circuit is in
closed state at each consumer, as indicated by reference numerals
22, 23 in the waveform (b) shown in FIG. 2. Such difference in the
detected signal levels is due mainly to the difference in the
length of the branches. Further, signal level at the signal
injector also is not necessarily constant. Therefore, the signal
level detected while no resonant circuit is connected to the line,
may also vary over a long period, as indicated by 21 and 24 in
waveform (b) of FIG. 2. Thus, it is possible to happen that the
signal level detected in a readout cycle without a consumer's
resonant circuit 6 connected is very near to that detected in
another readout cycle with another consumer's resonant circuit 6
connected to the line. In such a case, it is impossible to set a
proper threshold lever 25 for discriminating two kinds of
signals.
Thus, according to the conventional system, an assured and reliable
detection of the state of consumers' meters cannot be achieved
unless a limitation is set with respect to the variety in the
length of respective branches, the magnitude of consumer's loads
and the injection level of the signal.
Such a problem has been solved by this invention. Hereunder, this
invention will be described in detail in connection with an
embodiment of the invention.
The circuit shown in FIG. 3 is the same as that shown in FIG. 1,
components 101 to 116 in FIG. 3 corresponding to 1 to 16 in FIG. 1
respectively, except that the system shown in FIG. 3 is further
provided with an auxiliary switch 117 and a signal discriminator
118. In FIG. 4, index (i) designates the waveform of a signal
detected at the signal detector 111; (k) and (m) are waveforms
showing the operation of the auxiliary switches 117 which open and
close according to timings allotted to the respective consumers;
and (l) and (n) show the operation of switches 107 which correspond
to switches 7 in FIG. 1.
The operation of the system shown in FIG. 3 will be described
hereinafter also with reference to FIG. 4.
The signal injected through the signal input terminal 101 causes
the synchronous motor 104 to start by means of the resonant circuit
103 as explained in connection with the system shown in FIG. 1. The
synchronous motor 104 operates the switches 107 and 117 in a timing
peculiar to each consumer. In that case, a period allotted to the
consumer is divided into two parts, the first half being allotted
to the auxiliary switch 117 and the second half to the switch 107,
as indicated respectively by (k) and (l) for consumer No. 1, or by
(m) and (n) for consumer No. 2 in FIG. 4. That is, a detected
signal includes two pieces of information for each consumer. The
signal in the first half period represents the information of the
signal flow path with the resonant circuit 106 connected across the
consumer's load 113, the level of the signal depending on the
property and state of the line leading to the consumer and of the
consumer's load as well as on the level of the injection signal.
This detected signal is referred to as a reference signal
hereinafter. The level of the signal in the second half period
which is synchronized with the closure of the switch 107, varies
depending on whether the switch 109 is closed or opened, that is,
whether the resonant circuit 106 is connected across the load or
not. This signal in the second half period is referred to as a
readout signal hereinafter.
Thus, the entire sequence of the signal appearing at the output
terminal 112 of the signal detector 111 during a monitoring cycle
will be as shown in FIG. 4 (waveform (i)), for example. Such a
signal is led to the signal discriminator 118, the operation of
which will be explained with reference to the block diagram shown
in FIG. 5.
In FIG. 5 which is a block diagram example of the signal
discriminator 118, reference numeral 201 designates an input
terminal; 202 an input signal change-over circuit; 203 a signal
register; 204 a reference voltage producing circuit; 205 a voltage
comparator; 206 a timing control circuit which produces timing
pulses to coordinate the operation of respective component
circuits; 207 an input terminal for clock pulses; 208 to 210
control lines; and 211 an output terminal.
In the operation, a sequential signal such as the signal (i) shown
in FIG. 4 is applied to the input terminal 201. On the other hand,
a sequence of clock pulse is applied to the clock pulse input
terminal 207, the timing of the clock pulse corresponding to that
of the allotment of a monitoring period to each consumer. On the
basis of the clock pulse, the timing control circuit 206 provides
the change-over circuit 202 with an appropriate timing pulse
through the control line 208, by which the selection between the
reference signal and the readout signal is performed in the
change-over circuit. The firstly incoming signal, that is, the
reference signal is led to the register 203, and the peak value of
the signal is stored therein in an analogue mood. The reference
voltage producing circuit 204 multiplies an analogue voltage
imparted from the register 203 by a factor (not more than 1), for
example, by dividing the given voltage through a resistance voltage
divider to thereby produce the reference voltage. Meanwhile, the
next signal received during the ensuing half period, that is, the
readout signal, is changed over to the voltage comparator 205 by
the change-over circuit 202, where the readout signal is compared
with the reference voltage, an appropriate timing pulse being
applied to the comparator 205 from the control circuit 206 through
the control line 210. The result of the comparison appears at the
output terminal 211. A meter-reading for a consumer being thus
completed, a reset pulse is imparted to the register 203 through
the control line 209, and the signal discriminator becomes ready
for another meter-reading. The same operation is repeated for each
consumer.
As described above, the reference voltage given to the voltage
comparator 205 is reflecting factors particular to the distribution
line to the respective consumers. Thus, the threshold level for the
discrimination of signals automatically follows to the
above-mentioned factors of the respective consumer's lines, as the
reference voltage is renewed for each readout cycle as well as for
each consumer. The manner of the automatic adjustment of the
threshold level is shown in FIG. 6. Index (o) designates a detected
signal during a period allotted for a consumer who is distant from
the monitoring post and when the level of the injection signal is
low. It will be seen that the threshold level 301 is very low. On
the other hand, index (p) indicates a similar detected signal for
another consumer who is situated near to the monitoring post and
when the level of the injection signal is especially high. In such
a case, the threshold level 302 becomes high.
As the threshold level is automatically adjusted as described
above, the restrictions on the variety in the length of
distribution lines and in the consumer's loads as well as the
limitation on the deviation of the signal injection level can be
lifted, and a reliable readout operation is ensured.
Next, another embodiment of this invention will be described with
reference to FIG. 7 which shows a block diagram thereof and FIG. 8
which shows waveforms observed at an essential point in the
system.
In FIG. 7, circuit components designated by reference numerals 501
to 516 correspond to those designated by numerals 1 to 16
respectively. Therefore, explanation on these components will not
be repeated. Reference numeral 517 designates a further resonant
circuit tuned to a frequency near to but different from that of the
resonant circuit 506; numeral 518 a switch which closes and opens
in synchronization with the switch 507; numeral 519 a band-pass
filter; 520 an output terminal of the filter 519; numeral 521
another band-pass filter whose center frequency is different from
that of the filter 519; numeral 522 an output terminal of the
filter 521; numerals 523 and 524 integrators respectively; 525 a
voltage comparator; 526 an AND gate; 527 a control signal input
terminal of the AND gate 526; and 528 the output terminal of the
same AND gate.
In FIG. 8, index (q) indicates an example of the waveform of a
signal appearing at the output terminal 520, which has been
selected from the output of the signal detector 511 through the
filter 519; and the waveform indicated by index (r) is a signal
appearing at the output terminal 522, the output of the signal
detector 511 being filtered through the filter 521.
In the operation, two signals of near but different frequencies are
concurrently injected to the distribution line through the input
terminal 501 and the signal injector 502. In this respect, the said
two resonant circuits 506 and 517 are designed so as to
respectively tune with one and the other of the above two
frequencies. In the same manner as previously described in
connection with FIG. 1, one of the injected signals is picked up by
the resonant circuit 503 and causes the synchronous motor 504 to
start, which closes and opens the switch 507 in a timing such that
the availability of the distribution line as the signal channel or
flow path is allotted among all consumers by a time division
process. Also in the same manner as described previously, the
closure of the switch 507 makes it possible for the resonant
circuit 506 tuned to the said one frequency to be connected across
the consumer's load 513 when the switch 509 is closed. In this
embodiment, however, the switch 518 is closed concurrently with the
switch 507 to connect the resonant circuit 517 (which is tuned to
the said other frequency) across the load 513. Therefore, the
signal of the latter frequency necessarily passes the resonant
circuit 517 during the period allotted to the particular consumer
and it is detected by the signal detector 511. Such a detected
signal is also referred to as a reference signal.
On the other hand, the other signal having the said other frequency
is transmitted either through the resonant circuit 506 or by the
route of the load 513 and undergoing a heavy loss, depending on the
state of the watt-hour meter 510. Such a signal, as detected by the
signal detector 511, is also referred to as a readout signal.
The reference signal and the readout signal appearing at the
terminal 512 through the signal detector 511, are separated from
each other through the band-pass filters 519 and 521 tuned to the
respective frequencies of two signals, and the readout signal as
indicated by index (q) in FIG. 8 appears at the terminal 520, while
the reference signal as indicated by (r) in the same FIGURE appears
at the terminal 522. As is seen from FIG. 8, when the switch 509 is
in closed state in response to the state of the watt-hour meter
510, level 601 of the readout signal is substantially equal to
level 602 of the reference signal; whereas with the switch 509 in
opened state, level 603 of the readout signal is lower than level
604 of the reference signal. The respective signals appearing at
the respective terminals 520 and 522 are applied to the voltage
comparator 525, after the assuredness of the signals has been
enhanced through the respective integrators 523 and 524. Thus, the
state of the switch 509 (therefore, the state of the watt-hour
meter 510) in each consumer can be read out by extracting the
output of the voltage comparator in a proper timing through the AND
gate 526, namely, a clock pulse being applied to the clock pulse
input terminal 527 of the AND gate 526 in synchronization with the
previously described switch operating pulses ((c) to (h) in FIG.
2). With this embodiment, as described above, a distribution line
as a signal flow path is utilized for both reference and readout
signals through frequency-division, whereby the threshold level for
discriminating the readout signal is automatically adjusted.
The application field of the method and device of this invention is
extended by adapting the system so that the signal flow path, time-
or frequency-divided or in a frequency-divisional manner as
described above, is utilized also for control of loads and
confirmation of the control. An embodiment of such a modified
system will be described hereunder with reference to the block
diagram shown in FIG. 9 and waveforms shown in FIG. 10.
In FIG. 9, the components designated by reference numerals 701 to
708 are equivalent respectively to those designated by numerals 101
to 108 in FIG. 3. Also, numerals 711 to 718 correspond respectively
with 111 to 118 in FIG. 3. Therefore, description about such
components is spared. Numeral 709 designates a switch which is
connected in series with another switch in the same manner as the
switch 109 shown in FIG. 3 but which is controlled by a relay 809.
Numerals 801, 802 and 803 respectively designate series resonant
circuits tuned to an identical frequency; 804 a timer; 805 an
auxiliary circuit which causes the timer 804 to start in response
to the signal received through the resonant circuit 801 and stops
the timer 804 after the completion of one operation cycle; 806 a
switch for keeping the resonant circuit 801 disconnected from the
distribution line 814 after the start of the timer 804 until the
completion of one operation cycle; 807 and 808 switches operated by
the timer 804 in predetermined timing; 809 an output relay for
operating the above-mentioned switch 709 and also a switch 812 that
is the final control device; 810 a control circuit for turning-on
the output relay 809 in response to the signal received through the
resonant circuit 802; 811 another control circuit for turning-off
the same relay in response to the signal received through the
resonant circuit 803; and 813 the load (for example, street lights)
to be controlled by this system which is situated at a place near
the particular consumer's load 713.
In FIG. 10, index (s) indicates an example of a sequence of signal
injected to the line 714 through the signal injection terminal 701
and the signal injector 702, and index (t) a signal appearing at
the output terminal of the signal detector 711. Indexes (u), (v),
(w) and (x) indicate the operation of the switches 807, 808, 717
and 707 respectively.
In the operation, a high frequency signal (s) as shown in FIG. 10
is injected into the distribution line 714 by means of the signal
injector 702. The injected signal is picked up by the resonant
circuit 703 of each consumer and starts the rotation of the motor
(that is, a timer) 704 by means of the auxiliary circuit 705 in the
same manner as described in connection with FIG. 1 or FIG. 3. In
the present embodiment, however, the signal is also picked up by
the resonator 801, and the timer 804 is started by means of the
auxiliary circuit 805 substantially at the same time as the start
of the timer 704. Signal 901 shown in FIG. 10 indicates this
starting signal. The simultaneously started timers 704 and 804
close and open the respective switches 707, 717 and 807, 808 in the
timing shown in FIG. 10. (It is assumed that the circuit consisting
of components 801 to 812 is controller No. 2) That is, the switch
807 is first closed to connect the resonant circuit 802 across the
distribution line 714. If there is a signal 902 injected through
the signal injector 702 while the switch 807 is closed, as shown in
FIG. 10, that signal 902 is picked up by the resonant circuit 802
and conveyed to the control circuit 810 which turns on the output
relay 809 in response to the signal. Upon the actuation of the
relay 809, the switch (or contacts) 812 is closed to thereby turn
on the load 813. At the same time the switch 709 also is closed. As
will be clear from the above description, a command signal 902
intended to this controller No. 2 is detected exclusively by this
controller by preselecting the timings of the injection of the
command signal 902 and the closure of the switch 807 by the timer
804 so that both timings coincide with each other. During the
ensuing period 903, the switch 808 is closed ((v) in FIG. 10) to
connect the resonant circuit 803 across the line. In this example,
as shown in FIG. 10, there is no command signal during the period
903. Therefore, the control circuit 811 receives no signal from the
resonant circuit 803, and the output relay 809 maintains the closed
state. It will be understood, however, that if there is injected a
command signal during the period corresponding to the period 903 in
another control cycle, then the signal will be picked up by the
resonant circuit 803, and the relay 809 will be turned off by means
of the control circuit 811 thereby to cut the load 813. As
described above, a particular period in a monitoring and control
cycle is allotted to a particular command signal for a particular
controller, and the signal is received exclusively by the
particular controller by making a standby period at the said
controller coincide with the said particular period. Returning to
the operation of the system; as the timer 704 further rotates, the
switches 717 and 707 are closed and then opened in a timing
relation as indicated by (w) and (x) respectively in FIG. 10. By
this time, the signal is continuously injected as shown in the
waveform (s) of FIG. 10. With the switch 717 closed, therefore, the
injected signal 904 is necessarily transmitted through the resonant
circuit 706, and a reference signal 905 is detected by the signal
detector 711 in the same manner as described already in connection
with FIG. 3. During the ensuing period, the switch 707 is closed
either to connect the resonant circuit 706 across the line or not
depending on the state of the switch 709 also as described
previously. In this embodiment, however, the switch 709 represents
the state of the output relay 809 or the load switch 812.
Therefore, the readout signal 906 detected in the detector 711
reflects the state of the relay 809 or the switch 812. Thus, by
comparing the reference signal 905 and the readout signal 906,
response of the relay 809 to the above-mentioned command signal 902
can be confirmed at the site of the signal injection. Similarly, if
another controller, for example, controller No. 1, is connected to
another branch 715 of the distribution line, the controller No. 1
is controlled by a command signal which is injected in the period
907 or 908, and the operation of the controller can be confirmed by
comparing a reference signal 909 with the ensuing readout signal
910. In this example, the period ensuing from the end of the
response No. 2 is allotted to a sequential readout of watt-hour
meters of a number of consumers, the readout being performed in a
manner such as described in connection to FIGS. 3 and 4.
In the above embodiment, it has been assumed for the convenience of
the explanation that a plurality of timers (704, 804), resonant
circuits (703, 706, 801, 802, 803), control circuits (810, 811) and
auxiliary circuits (705, 805) are provided in each controller.
However, it will be understood that the plurality of components can
be respectively substituted by a single component, since those
plurality of components perform similar functions in different
periods respectively.
Summarizing the above description, a beginning portion of a
sequence of injected signal is allotted to control (or command)
signals and time divided among a plurality of controllers, and the
next portion to the response function in a similar manner, and the
last portion to the readout function for the consumer's watt-hour
meters. Therefore, control of loads and the confirmation thereof
can be achieved in a single operation cycle including the readout
of consumer's meters without impairing the meter-readout function
of the system.
Further, as the function of response or confirmation is similar to
that of meter-readout, the circuit components for the response
function can be replaced by those for the meter-readout. Moreover,
a single set of such components can be commonly used for both
functions simply by providing additional switches (not shown)
connected in parallel with the respective switches (for example,
switches 107, 109 and 117 in FIG. 3) and by setting the operation
periods of the additional switched differently from those of the
inherent switches (for example, switches 107 and 117). Thus, the
system is made simple and economical.
It will be understood that the order of the signal channels
allotted as shown in FIG. 10 can be changed if it is
desireable.
Moreover, though the object of the monitoring has been assumed to
be the meter-readout in the previous embodiments, it will be clear
that the same principle is applicable to other monitoring
functions.
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