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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a master station apparatus for a remote
supervisory control system. More specifically, it relates to a master
station apparatus for remotely monitoring the status of devices included
in remote stations such as power stations and substations of a power
system while remotely controlling a device selected at need.
2. Description of the Prior Art
A master station apparatus for a remote supervisory control system
comprises a monitor panel for constantly remotely monitoring the status of
devices included in remote stations and a control panel for selectively
remotely on-off controlling one of the devices. In general, the monitor
panel and the control panel for such a master station apparatus are
provided in most suitable structure for each supervisory control system in
response to the type and the scale of the system. With recent development
of a general video display employing a CRT, the monitor panel can be
provided in fixed hardware structure which is common to various systems.
However, the control panel or a console is still prepared for each system
in a custom-made manner, for the following reason:
A console in generality may be provided with alphanumeric keys so that an
arbitrary remote station or device can be selected through key operation.
However, designation of the remote station or device number through
combination of such alphanumeric keys requires complicated operation in
multiple stages. Further, a major accident may be caused by erroneous key
operation for selection and control, and the probability of such erroneous
key operation is extremely increased in the aforementioned selective
combination of the alphanumeric keys.
This goes against basic conditions of such a console, which is mainly
adapted to prevent erroneous device selection or control. Further, while
it is necessary to inspect a circuit breaker or a disconnector in a remote
station of, e.g., a power system with safety locking for disabling
operation of the device, such safety lock processing and confirmation of
the result of the processing cannot be easily performed in the
aforementioned console including the alphanumeric keys.
The inventor has proposed a master station apparatus for a remote
supervisory control system having a control panel of fixed hardware with
no such problems in Japanese Patent Laying-Open Gazette No. 39195/1983,
U.S. patent application No. 404,913 (Aug. 3, 1982) and German Patent
Application No. DE3231042A1. In this master station apparatus for a remote
supervisory control system, the control panel is formed by fixed hardware
with a general video display and a general card reader, and selection
cards corresponding to respective devices are previously prepared for
remote supervisory control so that an operator can insert a card in the
card reader and confirm the selection of the device by the video display,
thereby to control the device.
In this master station apparatus for a remote supervisory control system,
however, the operator must pick up a card for selecting the corresponding
device to insert the same in the card reader for every control operation,
leading to complicatedness in handling.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a master
station apparatus for a remote supervisory control system comprising fixed
hardware integrating a monitor panel and a control panel, through which an
operator can easily and reliably select and control a target device of a
target remote station by merely touching a touch panel provided on the
front surface of a video display.
According to the present invention, touch panel means is provided on the
display screen of video display means to discriminate the coordinates of a
position touched on the touch panel means. Status memory means stores the
current status of controlled devices, and pattern memory means stores
pattern data of connection or arrangement previously set in correspondence
to the respective monitored/controlled devices. Symbols indicating the
respective monitored/controlled devices are displayed on the video display
means, and when a part of the touch panel means corresponding to one of
the symbols is touched, the position coordinates thereof are read to
specify the corresponding one of the monitored/controlled devices and the
pattern data of the corresponding device and the symbol indicating the
current status of the same are displayed on the display means. When the
part corresponding to one of the displayed symbols is touched and the
position coordinates thereof are discriminated, a control command is
supplied to the corresponding monitored/controlled device.
Thus, according to the present invention, a target monitored/controlled
device can be selected by merely touching the touch panel means, whereby
complicatedness in operation can be eliminated.
In a preferred embodiment of the present invention, a plurality of
monitored/controlled devices are included in remote stations, and each
remote station supplies a status indication signal of the
monitored/controlled device included therein to the master station
apparatus in response to a control command from the same and in case of
automatic status change, and the master station apparatus updates the
content of the status memory means on the basis of the status indication
signal.
In the preferred embodiment of the present invention, therefore; it is
possible to continuously store the current status of the
monitored/controlled devices in the status memory means.
These and other objects, features, aspects and advantages of the present
invention will become more apparent from the following detailed
description of the present invention when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram showing an embodiment of the present
invention;
FIG. 2 is a schematic block diagram showing the structure of a line
interface as shown in FIG. 1;
FIG. 3 illustrates exemplary display of poke points for selecting remote
stations on a video display as shown in FIG. 1;
FIG. 4A illustrates exemplary structure of a touch panel;
FIG. 4B illustrates detailed conductor matrix detail of FIG. 4A;
FIG. 5 illustrates examples of a remote station diagram and device status
displayed on the video display as shown in FIG. 1;
FIG. 6 illustrates other examples of a remote station diagram and device
status displayed on the video display; and
FIGS. 7A, 7B and 7C are flow charts for concretely illustrating the
operation of the embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic block diagram showing an embodiment of the present
invention and FIG. 2 is a schematic block diagram of a line interface as
shown in FIG. 1, while FIG. 3 illustrates examples of poke points for
selecting remote stations displayed on a video display as shown in FIG. 1
and FIG. 4 illustrates the exemplary structure of a touch panel.
Referring to FIGS. 1 to 4, description is now made on the structure of the
embodiment of the present invention. A master station apparatus 1 is
connected with remote stations 11, 12, . . . , 1n (where n is the total
number of the remote stations) through transmission lines L.sub.1,
L.sub.2, . . . , L.sub.n. The remote stations 11, 12, . . . , 1n are
connected with monitored/controlled devices 111, . . . , 11m(1), 121, . .
. , 12m(2), . . . , 1n1, . . . , 1nm(n) respectively, where m(n) is the
total number of the controlled apparatuses in the n-th remote station.
The master station apparatus 1 includes a control circuit 2, a video
display 3 and a touch panel 4. The control circuit 2 includes a CPU 21, a
pattern memory 22, a status memory 23, an output control circuit 24, an
input control circuit 25, a line interface 5 and an alarm circuit 27,
which are connected with each other through a data bus 26. The pattern
memory 22 is adapted to store symbols of the respective remote stations
12, . . . , 1n and pattern data indicating connection or arrangement of
the controlled devices 111, . . . , 11m(1), 121, . . . , 12m(2), . . . ,
1n1, . . . , 1nm(n) displayed on the video display 3. The status memory 23
is adapted to continuously update and store the content thereof in
response to the status of the respective monitored/controlled devices 111,
. . . , 11m(1), 121, . . . , 12m(2), . . . , 1n1, . . . , 1nm(n) and
telemeters. The output control circuit 24 controls the display on the
video display 3. The input control circuit 25 analyzes coordinate input
signals of positions touched by an operator on the touch panel 4.
As shown in FIG. 2, the line interface 5 includes a microprocessor 6, a bus
interface 7, line buffers 81, 82, . . . , 8n and modems 91, 92, . . . ,
9n. The modems 91, 92, . . . , 9n are connected with the transmission
lines L.sub.1, L.sub.2, . . . , L.sub.n. These modems 91, 92, . . . , 9n
are adapted to perform frequency shift modulation (for example) of control
command signals against noise and for convenience of transmission to
transmit the same to the respective remote stations 11, 12, . . . , 1n
while demodulating codes transmitted from the respective remote stations
11, 12, . . . , 1n to rectangular pulses. The line buffers 81, 82, . . . ,
8n convert bit parallel codes supplied from the microprocessor 6 into bit
serial codes and add error checking codes to supply the same to the modems
91, 92, . . . , 9n while converting bit serial codes transmitted from the
respective remote stations 11, 12, . . . , 1n through the modems 91, 92, .
. . , 9n into bit parallel codes while performing code error checking. The
bus interface 7 is adapted to transfer data between the microprocessor 6
and the CPU 21 included in the control circuit 2 through the data bus 26.
Description is now briefly made on the operation of the line interface 5.
Signals from the respective remote stations 11, 12, . . . , 1n are
transmitted to the master station 1 through the transmission lines
L.sub.1, L.sub.2, . . . , L.sub.n, to reach the modems 91, 92, . . . , 9n
of the line interface 5. The modems 91, 92, . . . , 9n demodulate the
received signals to rectangular pulses, to supply the same to
corresponding ones of the line buffers 81, 82, . . . , 8n respectively.
The line buffers 81, 82, . . . , 8n convert bit serial codes of the
inputted rectangular pulses into bit parallel codes while checking code
errors, to supply interruption signals to the microprocessor 6 upon
receiving correct codes. The microprocessor 6 reads the received codes
from the line buffers providing the interruption signals, to supply the
same to the bus interface 7. The bus interface 7 receiving the codes
supplies interruption signals to the CPU 21 through the data bus 26.
Upon the receipt of the interruption signals, the CPU 21 receives the codes
from the bus interface 7 through the data bus 26 to update the contents of
the status memory 23. The data may be directly transmitted from the bus
interface 7 to the status memory 23 in case that a direct memory access
system is adopted.
In order to supply a control command to one of the remote stations 11, 12,
. . . , 1n, the CPU 21 provides the bus interface 7 with the control
content and the number of the target remote station through the data bus
26. Then the bus interface 7 supplies an interruption signal to the
microprocessor 6. Receiving the interruption signal, the microprocessor 6
reads the content inputted in the bus interface 7, to supply a code
indicating the control content to one of the line buffers 81, 82, . . . ,
8n on the basis of the number of the target remote station. The line
buffer supplied with the code converts the same from a bit parallel one
into a bit serial one while adding an error checking code, and supplies
the same to the corresponding one of the modems, which in turn performs
frequency shift modulation of the code to transmit the same to the target
remote station through the corresponding transmission line.
The touch panel 4 is a transparent panel which is mounted in proximity to
or in close contact with the front surface of the video display 3, so that
the position coordinates of a part touched by the operator are supplied to
the input control circuit 25 in the control circuit 2. Referring to FIGS.
4A and 4B, description is now made on the exemplary structure of the touch
panel 4. A base plate BP of a transparent insulator such as glass is
provided thereon with a plurality of transparent conductors H.sub.n,
H.sub.n+1, . . . in the horizontal direction and a plurality of
transparent conductors V.sub.m, V.sub.m+1, . . . in the vertical
direction, in the form of a matrix. Transparent insulators I are provided
in intersection points between the conductors H.sub.n, H.sub.n+1, . . . ,
and V.sub.m, V.sub.m+1, . . . Electrodes h.sub.n, h.sub.n+1, . . . and
v.sub.m, v.sub.m+1, . . . are mounted on edges of the conductors H.sub.n,
H.sub.n+1, . . . and V.sub.m, V.sub.m+1, . . . . The electrodes h.sub.n,
h.sub.n+1, . . . are externally provided with sequential control voltage
to perform scanning for checking voltage developed on the electrodes
v.sub.m, v.sub.m+1, . . . so that a potential is caused by contact
resistance through finger touch to enable detection of the coordinates of
the touched position by scanning timing, although the electrodes are
normally not in conduction.
The video display 3 may be formed by a CRT display, a liquid crystal
display, a projection type television display or the like.
The video display 3 displays poke points for selecting the remote stations
as shown in FIG. 3 so that, when the operator touches the poke point NORTH
S/S for example, the touch panel 4 inputs the coordinates of the position
displaying the poke point NORTH S/S in the input control circuit 25. The
CPU 21 confirms selection of NORTH S/S from the position coordinates
detected by the input control circuit 25 to read the pattern data of
connection or arrangement of NORTH S/S from the pattern memory 22 and
supply the same to the output control circuit 24, while reading the
current status of the controlled devices of NORTH S/S from the status
memory 23 to supply the same to the output control circuit 24. The output
control circuit 24 displays the connection or arrangement of NORTH S/S
superposing the status of the controlled devices (e.g., red in closed
status and green in open status) on the video display 3.
FIG. 5 illustrates examples of a remote station diagram and device status
displayed on the video display 3 as shown in FIG. 1. Referring to FIG. 5,
symbols 52R1 and 52R2 indicate receiving breakers, symbols 52P1 and 52P2
indicate transformer primary breakers, symbols 52S1 and 52S2 indicate
transformer secondary breakers, symbol 52T indicate a bus tie breaker and
symbols 52F1, 52F2, . . . , 52F6 indicate feeder breakers. The symbols are
displayed in red when the corresponding devices are in closed status while
being displayed in green when the same are in open status. Poke points OP
and CL are adapted to supply commands for switch control as hereinafter
described, and a reset poke point RS is adapted to regularly return the
display to the poke points for selecting the remote stations.
FIGS. 7A, 7B and 7C are flow charts for concretely illustrating the
operation of the embodiment of the present invention.
With reference to FIGS. 1 to 5, 7A, 7B and 7C, description is now
concretely made on the operation of the embodiment. At a step SP1, the CPU
21 determines whether or not an interruption signal is supplied from the
input control circuit 25. If no interruption signal is supplied from the
input control circuit 25, the process is advanced to a step SP2, to
determine whether or not an interruption indicating some change of status
is transmitted from any of the remote stations 11, 12, . . . , 1n to the
line interface 5. When no such code indicating status change is received,
the process is returned to the step SP1. When neither the input control
circuit 25 nor the line interface 5 outputs an interruption signal, the
CPU 21 repeats the operation of the steps SP1 and SP2.
When the video display 3 displays the poke points as shown in FIG. 3 and
the operator touches a position of the touch panel 4, the input control
circuit 25 discriminates the input coordinates of the touched position to
supply the discrimination output to the CPU 21 with an interruption
signal. The CPU 21 judges that the interruption signal is supplied from
the input control circuit 25 at the step SP1, and the process is advanced
to a step SP3. At the step SP3, a check is made as to whether or not the
image displayed on the video display 3 through the output control circuit
24 is that of the poke points for selecting the remote stations. This
check is made referring to the memory of a command precedingly supplied
from the CPU 21 to the output control circuit 24. When the CPU 21 has
confirmed at the step SP3 that the poke points for selecting the remote
stations as shown in FIG. 3 are displayed, the process is advanced to a
step SP4. At the step SP4, the CPU 21 discriminates the selected remote
station from the coordinates of the position touched by the operator on
the touch panel 4 on the basis of the output from the input control
circuit 25, and stores the selection of the remote station in a memory
(not shown) within the CPU 21.
At a step SP5, the CPU 21 supplies pattern data on connection or
arrangement of the remote station stored in the pattern memory 22 to the
output control circuit 24, to display the pattern data on the video
display 3. At a step SP6, the CPU 21 provides the status of the
corresponding devices of the remote station stored in the status memory
23, to display the status of the devices superposed over the pattern
display of the connection or arrangement of the remote station displayed
on the video display 3 at the step SP4. Then, at a step SP7, the CPU 21
makes a check on presence non presence of registration for automatic
status change of the controlled devices. Such registration is made when
automatic status change of the controlled devices is caused as hereinafter
described. Since no such registration is present in this case, the process
is returned to the step SP1.
As the result of the aforementioned operation, the video display 3 displays
the pattern data on connection or arrangement of the selected remote
station and the status of the monitored/controlled devices corresponding
to the remote station. The display picture when the remote station NORTH
S/S is selected, for example, is as shown in FIG. 5.
When, for example, the operator touches the device symbol of the receiving
breaker 52R1 as shown in FIG. 5, a corresponding position coordinate
signal is inputted from the touch panel 4 to the input control circuit 25,
which in turn discriminates the position coordinates to supply a
discrimination output signal to the CPU 21. The CPU 21 responsively judges
that the output signal is supplied from the input control circuit 25 at
the step SP1, and the process is advanced to the step SP3. At the step
SP3, the CPU 21 judges that the pattern of connection or arrangement of
the remote station is already displayed, and the process is advanced to a
step SP9. At the step SP9, the CPU 21 judges that the operator touches the
device symbol 52R1, and the process is advanced to a step SP10.
At the step SP10, a check is made as to whether or not registration of
automatic status change of the device is made, similarly to the
aforementioned step SP7. Since no automatic status change currently takes
place, the process is advanced to a step SP13, at which the CPU 21
discriminates the selected device 52R1 from the position coordinates of
the inputted device symbol, and registers the selection of the device 52R1
in the memory within the CPU 21. At a step SP14, the CPU 21 supplies a
command signal to the output control circuit 24 for flashing the
corresponding device symbol in order to inform the operator of that the
selection is registered. Then the process is again returned to the step
SP1.
Then, when the operator touches the poke point CL as shown in FIG. 5, the
CPU 21 executes the processing of the steps SP1, SP3 and SP9 similarly to
the above, while the same judges that the operator touches no device
symbol at the step SP9, and the process is advanced to a step SP15 as
shown in FIG. 7. At the step SP15, the CPU 21 judges that the operator
touches the poke point CL, and the process is advanced to a step SP16. At
the step SP16, the CPU 21 supplies the line interface 5 with a control
command for closing the corresponding device of the registered remote
station. The line interface 5 transmits the control command signal to the
corresponding remote station. Then the process is advanced to a step SP17,
at which the CPU 21 flashes the control poke point, i.e., the poke point
CL in this case, to inform the operator of that the control command is
transmitted to the remote station.
Then the process is again returned to the step SP1, so that the CPU 21
repeats the operation of the steps SP1 and SP2. When the control command
is transmitted to the corresponding remote station and the
monitored/controlled device responds to the control command, the result is
transmitted as a status change signal from the remote station to the
master station 1, so that the line interface 5 receives the status change
signal. Receiving the status change signal, the line interface 5 supplies
an interruption signal to the CPU 21. The CPU 21 responsively judges that
the interruption signal is supplied at the step SP2, and the process is
advanced to a step SP20 as shown in FIG. 7C. At the step SP20, the CPU 21
supplies the status change signal received by the line interface 5 to the
status memory 23, to update its content.
Then the process is advanced to a step SP21. Since the target
monitored/controlled device is currently under selection, the process is
further advanced to a step SP22, at which the CPU 21 supplies the updated
content of the status memory 23 to the output control circuit 24. At a
step SP23, the CPU 21 stops flashing of the corresponding device symbol
52R1 and the control poke point CL. The selection of the remote station
and the monitored/controlled device, control of the device and the result
of the responsive operation thereof are confirmed by such operation.
The CPU 21 is again returned to its initial state, to repeat the operation
of the steps SP1 and SP2. When the operator confirms the responsive
operation of the monitored/controlled device and touches the reset poke
point RS as shown in FIG. 5, the process is advanced to the steps SP1,
SP3, SP9 and SP15, at which the CPU 21 judges that the poke points CL and
OP are not touched and the process is advanced to a step SP18. At the step
SP18, the CPU 21 cancels the registration of selection of the remote
station and the monitored/controlled device. Then the CPU 21 reads data
for displaying the image of the poke points for selecting the remote
stations from the pattern memory 22 at a step SP19, to supply the data to
the output control circuit 24 for making the video display 3 display the
image of the poke points for selecting the remote stations. Then the CPU
21 is returned to its initial state.
The aforementioned operation is adapted to select and control a target
device of a remote station. Description is now made on the case where
automatic status change has occurred in a remote station. The CPU 21
generally repeats the operation of the steps SP1 and SP2. When status
change has occurred in a remote station and an automatic status change
signal is transmitted to the master station 1, the line interface 5
receives the automatic status change signal and the CPU 21 judges that an
interruption signal is supplied from the line interface 5 at the step SP2,
and the process is advanced to the step SP20 as shown in FIG. 7C. At the
step SP20, the CPU 21 supplies the content received by the line interface
5 to the status memory 23, to update its content. Then the process is
advanced to the step SP21 to check whether or not registration of device
selection is made. When the result of the check is "No," the process is
advanced to a step SP24.
At the step SP24, the CPU 21 registers the situation that the status change
of the corresponding monitored/controlled device occurred without a
control command from the master station 1, i.e., that the device status is
automatically changed in the memory of the CPU 21. Then the process is
advanced to a step SP25 to check whether or not the pattern of connection
or arrangement of the corresponding remote station is currently displayed.
When the pattern of the corresponding remote station is displayed by
chance, the process is advanced to a step SP26. At the step SP26, the CPU
21 supplies the output control circuit 24 with data indicating a new
status stored in the status memory 23, and then the process is advanced to
a step SP27, to supply the output control circuit 24 with a command for
flashing the symbol of the corresponding device.
However, such automatic status change of the monitored/controlled device
rather rarely take place in the remote station whose pattern of connection
or arrangement is currently displayed. In this case, the result of the
check at the step 25 is "No," and the process is advanced to a step SP28.
At the step SP28, the CPU 21 checks whether or not another remote station
is displayed, and when no such display is made, i.e., when the poke points
for selecting the remote stations are displayed, the process is advanced
to a step SP30. At the step SP30, the CPU 21 flashes the poke point of the
remote station causing the automatic status change. If another remote
station is displayed by chance, the process is advanced to a step SP29, at
which corresponding data are read from the pattern memory 22 to be
supplied to the output control circuit 24 in order to display the poke
points for selecting the remote stations on the video display 3, and then
the process is advanced to the step SP30. At the step SP30, the poke
points for selecting the remote stations are flashed and a sound is
generated from the alarm circuit 27 at this time. Then CPU 21 is returned
to its initial state.
The process is again returned to the step SP1 in the aforementioned manner,
and in this exemplary case, the video display 3 displays the poke points
for selecting the remote stations as shown in FIG. 3 and the poke point
for NORTH S/S having the automatic status change is flashed.
When the operator touches the flashed poke point NORTH S/S, an interruption
signal is supplied from the input control circuit 25 to the CPU 21, which
in turn discriminates the interruption signal at the step SP1, and the
process is advanced to the step SP3. At the step SP3, the CPU 21 judges
that the remote station selecting poke points are displayed, and the
process is advanced to the steps SP4, SP5 and SP6. At the steps SP4, SP5
and SP6, the CPU 21 registers the remote station selection and reads
pattern data from the area of the corresponding remote station in the
pattern memory 22 to supply the same to the output control circuit 24. The
CPU 21 further reads data indicating the status of the corresponding
monitored/controlled device from the status memory 23 to supply the same
to the output control circuit 24. Then the process is advanced to the step
SP7, at which the CPU 21 judges that the automatic status change is
registered through the step SP24 as hereinabove described with reference
to FIG. 7C, and the process is advanced to the step SP8 where the CPU 21
supplies the output control circuit 24 with a command signal for flashing
the symbol of the corresponding device.
Through the aforementioned operation, the video display 3 displays the
pattern of connection or arrangement of the remote station having the
automatic status change as shown in FIG. 5 for example, to flash the
symbol of the corresponding monitored/controlled device. If, for example,
the circuit breaker 52R2 in NORTH S/S has tripped, the symbol 52R2 in FIG.
5 will be changed to green display with flashing to indicate the switched
state. When the operator touches the flashed symbol 52R2, the CPU 21
discriminates an interruption signal from the input control circuit 25 at
the step SP1 as shown in FIG. 7A and performs the operation of the steps
SP3 and SP9, and the process is advanced to the step SP10. At the step
SP10, the CPU 21 judges that the automatic status change is registered,
and then cancels the registration of the automatic status change at the
step SP11. Then the CPU 21 supplies the output control circuit 25 with a
command signal to stop flashing of the symbol of the corresponding
monitored/controlled device at the step SP12. The operator completes
confirmation of the automatic status change of the corresponding
monitored/controlled device 52R2 by the stoppage of flashing of the
symbol.
When the operator touches the reset poke point RS as shown in FIG. 5, the
CPU 21 executes the operation of the steps SP1, SP3 and SP9 and the
process is advanced to the step SP15. At the step SP15, the CPU 21 judges
that the poke points CL and OP are not touched, and cancels registration
of remote station selection at the step SP18. The CPU 21 further reads
data for displaying the remote station selecting poke points from the
pattern memory 22 to supply the same to the output control circuit 24 for
display on the video display 3, and is returned to its normal state.
A dedicated poke point may be independently provided to commonly confirm
status change with respect to all of the controlled devices displayed on
the screen to stop flashing thereof.
Although a control command is immediately transmitted to the corresponding
device of the corresponding remote station when the operator touches the
poke point CL or OP for switch control in the above embodiment, it is also
possible to execute control operation to be performed upon confirmation
thereof in consideration of importance of the control operation.
Description is now made on such an embodiment.
FIG. 6 illustrates exemplary display on a video display in another
embodiment of the present invention.
The structure of FIG. 6 is different from that of FIG. 5 in that a poke
point EX for indicating execution is provided under switch control poke
points CL and OP. Further, no control code is transmitted immediately upon
touch on the switch control poke point CL or OP but the poke point CL or
OP is flashed to confirm control operation, and then the execution command
poke point EX is touched to transmit a control command signal for the
confirmed control operation.
Although selection of the remote station and the device is confirmed only
through the control circuit 2 of the master station 1 in the
aforementioned embodiment, another embodiment is possible where selection
code is transmitted to the corresponding remote station and the selection
is confirmed by the answer-back code.
The switch control in the aforementio | | |
