Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Reexamination Certificate
2000-07-25
2003-03-25
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
Reexamination Certificate
active
06538865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication system that comprises a plurality of nodes connected in common to two-wire transmission lines and more particularly to a fault-detecting device for detecting a fault such as a break, a short circuit, and the like of transmission lines.
2. Detailed Description of the Related Art
As shown in
FIG. 1
, in a prior art communication system, two-wire transmission lines
1
,
2
are connected with transmission/reception circuits
3
1
-
3
n
at a plurality of nodes. All the transmission/reception circuits
3
1
-
3
n
comprise the same components. Positive potential Vcc (for example, 5 V) is supplied to one end of the transmission line
1
via a terminal resistor
4
and positive potential Vcc is supplied to the other end via a terminal resistor
5
in the same way. Ground potential Vg (for example, 0V) is supplied to one end of the transmission line
2
via a terminal resistor
6
and ground potential Vg is supplied to the other end via a terminal resistor
7
in the same way.
In the transmission/reception circuit
3
1
, a two-way I/O filter
11
is connected to the transmission lines
1
,
2
via a connector
12
. Connecting terminals A
1
, A
2
are provided for connecting the I/O filter
11
to the transmission lines
1
,
2
and connecting terminals B
1
, B
2
arranged as opposed to the connecting terminals A
1
, A
2
. A transmission signal is individually supplied to the connecting terminals B
1
, B
2
via a non-inverting amplifier circuit
13
and an inverting amplifier circuit
14
. In addition, bias circuits
17
,
18
are connected to the connecting terminals B
1
, B
2
of the filter
11
via AC coupling circuits
15
,
16
which comprise a resistor and capacitor, respectively. Each of the signals provided by the bias circuits
17
,
18
serves as a reception signal via a comparator
19
.
Upon outputting the transmission signal, the signal is amplified by the non-inverting amplifier circuit
13
and amplified in an inverting manner by the inverting amplifier circuit
14
as well. Transmission signals opposite in phase to each other are supplied to the filter
11
from the non-inverting amplifier circuit
13
and the inverting amplifier circuit
14
. The filter
11
serves as a low-pass filter to allow the transmission signals to pass individually therethrough. An output transmission signal from the non-inverting amplifier circuit
13
passes through the filter
11
and is thereafter supplied to the transmission line
2
as an information signal. An output transmission signal from the inverting amplifier circuit
14
passes through the filter
11
and is thereafter supplied to the transmission line
1
as an information signal.
On the other hand, the information signals, opposite in phase to each other and transmitted through each of the transmission lines
1
,
2
are supplied to the filter
11
. The filter
11
acts as a low-pass filter on each of. these information signals to output the signals to the AC coupling circuits
15
,
16
. Each of the AC coupling circuits
15
,
16
extracts AC components of the information signals and supplies the components to the bias circuits
17
,
18
, respectively.
For example, as shown in
FIG. 2A
, consider the case where a signal A transmitted through the transmission line
1
and a signal B transmitted through the transmission line
2
vary as opposed in phase to each other. As shown in
FIG. 2B
, the bias circuit
17
applies a bias voltage to the information signal A to obtain a biased signal BIASA, while the bias circuit
18
applies a bias voltage to the information signal B to obtain a biased signal BIASB. As shown in
FIG. 2C
, the comparator
19
detects each of the output signals BIASA, BIASB from the bias circuits
17
,
18
as a reception signal RX
0
.
When a break has occurred in the transmission line
1
, only signal B is transmitted in the transmission line
2
. Accordingly, as shown in
FIG. 2D
, the biased signal BIASA remains constant, whereas the biased signal BIASB, transmitted through the transmission line
2
, to which a bias voltage has been applied changes like the signal B. The comparator
19
compares the constant biased signal BIASA and the biased signal BIASB to obtain a reception signal as shown in FIG.
2
E. This holds true even when the transmission line
1
is grounded or when the transmission line
2
is broken or grounded.
Incidentally, no reception signals could be detected without the bias circuits
17
,
18
when a break occurs in the transmission line
1
since the signals A, B to be inputted into the comparator
19
would have the waveforms shown in FIG.
2
F.
A fault detecting device for detecting a fault such as a break or a short circuit or the like on the transmission lines
1
,
2
comprises comparators
20
,
21
and mismatch detecting circuits
22
,
23
. The comparator
20
compares the biased signal BIASA with a threshold value Vth. A high level output is obtained when the biased signal BIASA is equal to or less than the threshold value Vth, whereas a low level output is obtained when the biased signal BIASA is greater than the threshold value Vth. The output is supplied to the mismatch detecting circuit
22
as an individual reception signal RX
1
. The mismatch detecting circuit
22
reads, in phase with a sampling clock, each of the reception signals RX
0
, RX
1
of the comparators
19
,
20
. The mismatch detecting circuit
22
provides a low level output when the levels of the read reception signals RX
0
, RX
1
coincide with each other. On the other hand, when the levels of the reception signals RX
0
, RX
1
do not coincide with each other, the mismatch detecting circuit
22
provides a high level output that shows that a fault has occurred on the transmission line
1
.
Likewise, the comparator
21
compares the biased signal BIASB with the threshold value Vth. A low level output is obtained when the biased signal BIASB is equal to or less than the threshold value Vth, whereas a high level output is obtained when the biased signal BIASB is greater than the threshold value Vth. The output is supplied to the mismatch detecting circuit
23
as an individual reception signal RX
2
. The mismatch detecting circuit
23
reads, in phase with the sampling clock, each of the reception signals RX
0
, RX
2
of the comparators
19
,
21
. The mismatch detecting circuit
23
provides a low level output when the levels of the read reception signals RX
0
, RX
2
coincide with each other. On the other hand, when the levels of the reception signals RX
0
, RX
2
do not coincide with each other, the mismatch detecting circuit
23
provides a high level output that shows that a fault has occurred on the transmission line
2
.
In response to the high-level output showing a fault, for example, the transmission/reception circuit
3
1
activates fault corrective functions such as generating an alarm or stopping transmission and/or reception operation.
Other transmission/reception circuits
3
2
-
3
n
also have the same configuration and functions as those of the transmission/reception circuit
3
1
. Incidentally, a device that detects a fault on a transmission line based on signal levels are disclosed in Japanese Patent Laid-Open Publications No. Hei 5-147479 and No.Hei 5-75629.
However, once it is detected that the level of the signal transmitted through the transmission line
1
or
2
is abnormal in such prior art fault-detecting device of a communication system, the device judges immediately that a fault has occurred in the transmission line
1
or
2
. Accordingly, even a disturbance such as a noise that would never exert an adverse effect on the transmission/reception operation of the system would cause the device to judge that a fault occurred in the transmission line
1
or
2
. This would cause the fault corrective functions to work unnecessarily.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the aforementioned circumstances, an object of the present invention is to provide a fault-detecting device
Hashimoto Hiroshi
Iwamoto Kazuya
Nagatani Yuji
Honda Giken Kogyo Kabushiki Kaisha
Kitov Z
Sircus Brian
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