JPH11127178A - Feeder for signal transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for labor and time for matching a polarity and to attain simple connection, when connecting the feeder to a signal transmission line. SOLUTION: This feeder 1 is provided with a polarity detection section 4, a polarity changeover section 5 and a control circuit section 6. The polarity detection section 4 detects the polarity (polarity of a DC voltage applied to a signal transmission line 20) of a signal transmission line 20. Further, the polarity changeover section 5 switches the polarity of a DC voltage applied from a power supply section 2 to the signal transmission line 20. Then, the control circuit section 6 switches and controls the polarity switching section 5, so that the polarity of the signal transmission line 20 detected by the polarity detection section 4 coincides with the polarity of the DC voltage applied from the power supply section 2. Thus, the polarity of the DC voltage applied from the power supply section 2 is made to automatically match with the polarity of the signal transmission line 20, then a worker connects the feeder 1 without being aware of the polarity of the signal transmission line 20 and labor and time to make them match with the polarity are not required in the connection of the feeder 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for a signal transmission system used for an air conditioning system, a lighting control system, and the like in a building or an apartment house.

[0002]

2. Description of the Related Art A conventional signal transmission system of this type is shown in FIG. 8 (see "Home Bus Development Research", page 37 (July 1985, Home Bus System Development Research Committee). ). As shown in FIG. 8, a plurality of signal transmission devices 10 and a power supply device 40 are connected to a two-wire signal transmission line 20, and both ends of the signal transmission line 20 are terminated by terminating resistors Rt.

The power supply device 40 includes a DC power supply 41 for obtaining a DC from a commercial AC power supply and the like and a choke coil 3 for removing a signal component flowing through the signal transmission line 20. Is transmitted to the signal transmission path 20 via the choke coil 3. On the other hand, the signal transmission device 10 includes a power receiving circuit 11 that receives the DC power transmitted to the signal transmission line 20 to obtain an operation power source, and a signal component removing device provided between the signal transmission line 20 and the power reception circuit 11. , A pulse transformer 13 connected to the signal transmission path 20, and a power supply from the power receiving circuit 11. The power supply circuit 11 operates and receives illumination according to a control signal from control means (not shown) or a switch operation signal. And an interface unit 14 for outputting a signal or the like for controlling a load to the signal transmission line 20 via the pulse transformer 13.

In the above conventional system, the pulse transformer 1 is transmitted from the interface unit 14 of each signal transmission device 10.
By transmitting a bipolar pulse signal (bipolar pulse signal) to the signal transmission line 20 via the signal transmission line 3, communication between the signal transmission devices 10 is performed, and power is supplied using the low-pass filter characteristic of the choke coil 12. The power supply by the device 40 and the communication by the signal transmission device 10 are both performed on the common signal transmission path 20.

When the system is relatively small as in the above-described conventional example, power can be supplied by a single power supply device 40. However, when the number of signal transmission devices 10 increases and the system becomes large, the entire system becomes large. Therefore, the power consumption supplied to the signal transmission line 20 needs to be increased accordingly. In this case, the simplest method of increasing the power supply capacity is to connect a plurality of power supply devices 40 to the signal transmission line 20 with their polarities aligned as shown in FIG.

As another method, as shown in FIG.
No. transmission line 20 is connected to trunk line 21 and branch line 22 ₁, 22_Two... and minute
Ke, each branch line 22₁... Capacitor C for DC cut₁To
Provide each branch line 22₁... a signal from one power supply device 40 for each
There is a method of feeding power to the transmission device 10 (Japanese Patent Laid-Open No. 3-2).
No. 4837). As still another method, FIG.
As shown in FIG.
Sa C_TwoBy connecting the plurality of signal transmission paths 20 in a DC manner.
And the power is supplied to each of the divided areas of the signal transmission path 20.
A method of providing power by providing an electric device 40, the concept of a trunk line
Although there is no, it is based on the same idea as the above method
(See JP-A-9-64894).

[0007]

However, in any of the above-mentioned methods, there is a restriction that the polarities of the plurality of power supply devices 40 are matched, or the places where the power supply devices 40 can be connected are limited. Therefore, the power supply device 40 must be connected to the signal transmission line 20 after being designed in advance. There is also a method of using a connector or the like so that the polarity can be easily changed. However, there is a possibility that erroneous connection between the wiring in the signal transmission device 10 and the connector may occur.

The present invention has been made in view of the above circumstances, and an object thereof is to eliminate the trouble of adjusting the polarity when connecting a power supply device to a signal transmission line, thereby enabling easy connection. It is an object of the present invention to provide a power supply device for a simple signal transmission system.

[0009]

According to a first aspect of the present invention, in order to achieve the above object, a plurality of signal transmission devices and one or more power supply devices are connected by a signal transmission line, and a signal is transmitted from the power supply device. A power supply for a signal transmission system that applies a direct current to a transmission line to supply power to each signal transmission device and transmit signals between the signal transmission devices via the signal transmission line, and detects the polarity of the signal transmission line. Polarity detecting means, and polarity switching means for switching the applied polarity to the signal transmission path so as to match the polarity detected by the polarity detecting means, the applied polarity of the power supply device of the signal transmission path Since the switching is automatically performed according to the polarity, it is not necessary to adjust the polarity when connecting the power supply device to the signal transmission line, and the connection can be easily performed.

According to a second aspect of the present invention, in the first aspect of the present invention, the polarity detecting means is turned on / off according to the polarity of the signal transmission path.
It is characterized by having a switch element that turns off, and can detect the polarity of the signal transmission path with a simple configuration. According to a third aspect of the present invention, in the first or second aspect, a timer means for performing a predetermined time count at the time of a power failure, and a nonvolatile memory for storing the polarity of the signal transmission path before the time count by the timer means is started. Storage means, and the polarity switching means switches the polarity so that the polarity detected by the polarity detection means and the polarity applied to the signal transmission path coincide with each other when power is restored after the time count in the timer means is completed, When the power is restored before the end of the time counting by the timer means, the polarity is switched so that the polarity stored in the storage means and the applied polarity to the signal transmission line coincide with each other. If power is restored before, it is determined that a short-term power failure such as an instantaneous power failure has occurred, and the polarity is switched to the polarity stored in the storage means, and time counting is performed. If the power supply device operates after a short-term power failure such as an instantaneous power failure, it is determined that the power supply has been disconnected from the signal transmission path for a long period of time if the power failure continues, and the polarity is detected by the polarity detection means. Can be smoothly resumed.

According to a fourth aspect of the present invention, in order to achieve the above object, a plurality of signal transmission devices and one or more power supply devices are connected by a signal transmission line, and a direct current is applied from the power supply device to the signal transmission line. A power supply device for a signal transmission system that supplies power to each of the signal transmission devices and performs signal transmission between the signal transmission devices via the signal transmission path. Power supply polarity detection means for detecting the polarity of alternating current, polarity detection means for detecting the polarity of the signal transmission path, and power supply when the polarity detected by the power supply polarity detection means matches the polarity detected by the polarity detection means. Control means for supplying power from the means to the signal transmission line, so that it is not necessary to adjust the polarity when connecting the power supply device to the signal transmission line, and the connection can be easily performed.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the power supply polarity detecting means performs a half-wave rectification of the alternating current supplied from the power supply means, and a capacitance element charged via the rectification element. And the configuration of the power supply polarity detecting means can be simplified.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a block diagram showing a signal transmission system according to the present embodiment. The configuration of a signal transmission device 10 and the like other than the power supply device 1 which is the gist of the present invention is common to the conventional example. Therefore, common portions are denoted by the same reference numerals and description thereof is omitted, and only the power supply device 1 which is a feature of the present embodiment will be described.

The power supply device 1 of the present embodiment includes a power supply unit 2 for generating a DC power supply from a commercial AC power supply or the like, and a signal transmission path 20.
Choke coil 3 for removing signal components flowing through
A polarity detector 4 for detecting the polarity of the signal transmission line 20 (the polarity of the DC voltage applied to the signal transmission line 20), and a polarity switching for switching the polarity of the DC voltage applied from the power supply unit 2 to the signal transmission line 20 And a control circuit unit 6 for switching the polarity switching unit 5 so that the polarity of the signal transmission path 20 detected by the polarity detection unit 4 and the polarity of the DC voltage applied from the power supply unit 2 match. ing.

The power supply unit 2 has a configuration in which, for example, a commercial AC power supply is stepped down to an appropriate level by a transformer (not shown) and rectified and smoothed to obtain a DC voltage. Figure 2 shows the configuration of the polarity detection unit 4, the signal transmission line 20 connected to the line 20 ₁ ', 20 _2' resistance R ₁ between the Zener diode ZD ₁ and the input side of the photocoupler PC ₁ (emission Diode LD ₁ ), a resistor R ₂ , a Zener diode ZD ₂ and a photocoupler P
The input side (light emitting diode LD ₂ ) of C ₂ is connected in series in the opposite direction, and the output side (photo transistor PT ₁ , PT ₂ ) of each photocoupler PC ₁ , PC ₂ is connected to the control circuit section 6.
Connected to That is, when the polarity of one of the lines 20 ₁ ′ is positive and a voltage higher than the zener voltage of the zener diode ZD ₁ is applied, the zener diode Z 1
Photocoupler PC ₁ is turned on by D ₁ becomes conductive, the Zener diode ZD ₂ is photocoupler PC ₂ is turned off in a non-conducting. On the other hand, when the polarity of the other line 20 ₂ ′ is positive and a voltage equal to or higher than the Zener voltage of the Zener diode ZD ₂ is applied, the Zener diode ZD ₂ conducts and the photocoupler PC ₂ is turned on, and the Zener diode ZD ₂ turns on. diode ZD ₁ photocoupler PC ₁ is turned off in a non-conducting. As a result, the photo couplers PC ₁ and PC ₂ are turned on and off.
By turning off, the polarity of the signal transmission line 20 can be detected in the control circuit unit 6. Note that the photocouplers PC ₁ , P
When both C ₂ are off, a state where no DC voltage is applied to the signal transmission path 20 (for example, a power failure or signal transmission path 2
0 is a state in which no power supply device 1 is connected).

The polarity switching section 5 includes a relay (not shown) driven and controlled by the control circuit section 6 and a pair of switching contacts 5a, 5a, 5b, 5b provided at an output end of the power supply section 2.
And a relay contact for switching to the common contacts 5c, 5c connected to the signal transmission path 20 via the choke coil 3. Thus, the common contacts 5c, 5c are replaced with the switching contacts 5a, 5
The polarity of the DC voltage applied from the power supply unit 2 to the signal transmission line 20 can be switched by switching connection to a, 5b, and 5b.

The control circuit section 6 has a CPU as a main component,
The detection signal (photocoupler PC ₁ , P
Depending on the C ₂ ON-OFF signal), as to switching control by driving the relay polarity switching portion 5 so that the polarity of the DC voltage applied from the polarity and the power supply unit 2 of the signal transmission path 20 matches is there. That is, in this embodiment, the control circuit unit 6 and the polarity switching unit 5 constitute a polarity switching unit. When no voltage is applied to the signal transmission line 20, the control circuit unit 6 controls the polarity switching unit 5 so as to have a default polarity stored in advance.

According to this embodiment, when a plurality of power supply devices 1 are connected to the signal transmission line 20, the polarity detection unit 4 of each power supply device 1 detects the polarity of the signal transmission line 20 and controls the control circuit unit. The switch 6 controls the switching of the polarity switching unit 5 so that the polarity of the DC voltage applied from its own power supply unit 2 can automatically match the polarity of the signal transmission path 20. Therefore, the installer can connect the power supply device 1 without being aware of the polarity of the signal transmission path 20, and there is no need to adjust the polarity when connecting the power supply device 1. It should be noted that the power supply apparatus becomes large if one power supply is used. However, if the power supply is distributed by a plurality of power supply apparatuses 1 as in the present embodiment, the individual power supply apparatuses 1 can be reduced in size. Since the power supply device 1 most suitable for the signal transmission system can be selected, there is an advantage that the system cost can be reduced.

FIG. 3 shows a transistor Q ₁ instead of a relay.
₃ shows an example in which the polarity switching unit 5 is configured by connecting the .about.Q4 in a bridge. Here, with the power supply unit 2 to the AC voltage AC is stepped down by the transformer T, to create a DC voltage to be supplied to the signal transmission line 20 is rectified and smoothed by the diode bridge DB ₁ and a smoothing capacitor C _3, the diode bridge The operation power supply of the control circuit unit 6 is created by rectifying and smoothing with the DB ₂ and the smoothing capacitor C ₄ .

If the polarity switching unit 5 is formed by using the bridge circuit of the transistors Q _{1 to} Q _{4 in} this manner, the size of the polarity detection unit 5 can be reduced as compared with the case where a relay is used, and the contact welding and the like can be performed. This has the advantage that the occurrence of the problem described above can be avoided. (Embodiment 2) FIG. 4 is a block diagram showing a power supply device 1 'of this embodiment. However, since the basic configuration is the same as that of the first embodiment, the same reference numerals are given to the common parts and the description thereof will be omitted, and only the features that are the features of the present embodiment will be described.

In the first embodiment, when an instantaneous power failure or the like occurs, the control circuit unit 6 switches the polarity by the polarity switching unit 5 in accordance with the detection result of the polarity detection unit 4 each time.
It takes time for the power supply device 1 to be connected to the signal transmission path 20, and there is a possibility that the power supply operation cannot be smoothly restarted. Therefore, in the present embodiment, a timer unit 7 that performs a predetermined time count at the time of a power failure and a non-volatile memory unit 8 that stores the polarity of the signal transmission path 20 before the timer unit 7 starts time counting. , Control circuit section 6
However, when the power is restored after the time count in the timer unit 7 is completed, the polarity detected by the polarity detection unit 4 and the signal transmission path 2
The polarity is switched by controlling the polarity switching unit 5 so that the applied polarity to 0 coincides with the polarity. When the power is restored before the time count in the timer unit 7 is completed, the polarity and the signal stored in the memory unit 8 are restored. The polarity is switched by controlling the polarity switching unit 5 so that the polarity applied to the transmission line 20 matches.

When a power failure occurs, the timer section 7 receives power supply from a backup power supply such as a battery, starts time counting for a predetermined time, and outputs a time-up signal after the time counting is completed. On the other hand, the control circuit unit 6 determines that a relatively short-term power failure such as an instantaneous power failure has occurred unless a time-up signal is output from the timer unit 7 when the operation is resumed due to power recovery. If a time-up signal is output from the unit 7, a long-term power failure or signal transmission path 2
It is determined that the connection to 0 has been disconnected (including the initial connection). If it is determined that a short-term power failure has occurred, the polarity detection unit 4 does not perform polarity detection, and the control circuit unit 6 controls the polarity switching unit 5 so as to match the polarity read from the memory unit 8 so as to match the polarity. The polarity applied from the unit 2 to the signal transmission path 20 is switched. Further, when it is determined that the power failure is a long-term power failure or the like, the polarity detection unit 4 detects the polarity of the signal transmission path 20 in the same manner as the power supply device 1 according to the first embodiment.
The control circuit unit 6 controls the polarity switching unit 5 so as to match the detected polarity to switch the applied polarity from the power supply unit 2 to the signal transmission path 20, and simultaneously stores the data of the switched polarity in the memory unit 8. .

According to the present embodiment, it is determined whether a relatively short-term power outage such as an instantaneous power outage or a long-term power outage or disconnection has occurred by using the time count of the timer unit 7. However, in the case of a short-term power failure, the control circuit unit 6 controls the polarity switching unit 5 so as to match the polarity stored in the memory unit 8, so that a short-term power failure such as an instantaneous power failure occurs. The operation of the power supply device 1 'can be smoothly restarted when an error occurs.

(Embodiment 3) FIG. 5 shows a power supply device of this embodiment.
And FIG. 6 is a schematic circuit diagram thereof.
You. Note that the basic configuration of the present embodiment is also different from the configuration of the first embodiment.
Since they are common, the same parts are assigned the same reference
Description is omitted. In the power supply device 1 ″ of the present embodiment,
Secondary winding n_TwoSwitch the AC voltage generated across
Smoothing capacitor C via element 30_ThreeSmoothing with DC
Pressure and the secondary winding n of the transformer T_ThreeOn both ends of
The resulting AC voltage is ₁And smoothing capacitor C_Four
DC voltage rectified and smoothed by a 3-terminal regulator IC₁To
So that the voltage is converted to a constant voltage of 5 V and supplied to the control circuit unit 6.
And the primary winding n of the transformer T₁Connected to
Detects polarity (or phase) of AC voltage of AC power supply AC
Resistance R_FiveAnd diode D_TwoA power pole consisting of
A sex detector 32 is provided. Here, the switch element 30
Is a package consisting of a photodiode and a phototransistor.
It is composed of a photo MOS relay
The switching element Q is controlled by the control circuit unit 6._FiveOn
It is energized by turning it off and turned on and off.
You.

On the other hand, the power supply polarity detecting section 32 connects one end of a resistor R _{5 to} the anode of the rectifying diode D ₁ , and connects the other end of the resistor R ₅ to a signal input end of the control circuit section 6. It is constructed by inserting the diode D ₂ between the signal input terminal and a power supply terminal. And Thus, although the AC voltage generated in the secondary winding n ₃ of the transformer T by the diode D ₁ is being half-wave rectifier, the diode D ₁
The conduction period (alternating-current power supply AC of the alternating voltage half period) in the diode D ₂ is the control circuit 6 of the signal input to the 3-terminal regulator IC ₁ of the output voltage by conductive (DC 5
V) is input, and during the non-conducting period of the diode D ₁ (the remaining half cycle of the AC voltage of the AC power supply AC), the diode D ₂ becomes non-conducting. Becomes almost 0 V and no signal is input. That is, the conduction of the power supply polarity detection unit 32 in the diode D ₂ ·
The polarity (or phase) of the AC voltage of the AC power supply AC is detected by the non-conduction, and a detection signal is supplied to a signal input terminal of the control circuit unit 6.

On the other hand, the control circuit 6 from the power source polarity detecting unit 32 has received the detection signal, the polarity of the polarity detection section 4 detects at signal transmission line 20, the AC generated in the secondary winding n ₂ of the transformer T The switching element ₃ is synchronized with the cycle of the AC power supply AC so that the polarity of the DC voltage obtained by smoothing the voltage by the smoothing capacitor C ₃ via the switching element 30 matches.
The on-off and AC voltage generated in the secondary winding n ₂ 0 to half-wave rectification. That is, as shown in FIG. 7, the polarity of the DC voltage supplied to the signal transmission line 20 can be switched by switching the timing at which the control circuit unit 6 turns on and off the switch element 32 every half cycle of the AC power supply AC. The rectifying function of the diode bridge DB ₁ and the switching function of the polarity switching unit 5 in the circuit configuration shown in FIG.
(However, in FIG. 7, the polarity of the AC power supply AC is indicated by an arrow, a state where power is not supplied to the signal transmission line 20 is represented by a resistor, and a state where power is supplied is represented by a battery symbol in FIG. 7. It is simply expressed.) When the polarity cannot be detected by the polarity detection unit 4 (in FIG. 7, it is described as “no power”), the switch element 32 may be turned on / off at default timing.

As described above, according to the present embodiment, according to the polarity of the AC power supply AC detected by the power supply polarity detection unit 32,
Since the switch element 30 is turned on and off so that the polarity of the DC voltage supplied to the signal transmission line 20 matches the polarity of the signal transmission line 20, the AC voltage of the AC power supply AC is half-wave rectified. The installer can connect the power supply device 1 ″ without being conscious of the polarity of the signal transmission path 20, eliminating the need to adjust the polarity when the power supply device 1 ″ is connected. Since the polarity can be switched by one switch element 30 instead of the relay and the transistors Q _{1 to} Q ₄ , there is an advantage that the power supply device 1 ″ can be reduced in size and cost.

[0028]

According to the first aspect of the present invention, a plurality of signal transmission devices and one or more power supply devices are connected by a signal transmission line, and a direct current is applied from the power supply device to the signal transmission line to thereby provide a signal transmission device. A power supply device for a signal transmission system that supplies power to each signal transmission device via a signal transmission line and performs signal transmission, and a polarity detection unit that detects a polarity of the signal transmission line,
There is provided polarity switching means for switching the applied polarity to the signal transmission path so as to match the polarity detected by the polarity detection means. Therefore, the applied polarity of the power supply device is automatically switched according to the polarity of the signal transmission path. Therefore, there is an effect that it is not necessary to adjust the polarity when connecting the power supply device to the signal transmission path, and the connection can be easily performed.

According to the second aspect of the present invention, since the polarity detecting means has a switch element which is turned on / off in accordance with the polarity of the signal transmission line, the polarity of the signal transmission line can be detected with a simple configuration. . The invention according to claim 3 comprises timer means for performing a predetermined time count at the time of a power failure, and non-volatile storage means for storing the polarity of the signal transmission path before the time count by the timer means is started. When the power is restored after the time counting by the timer means is completed, the polarity is switched so that the polarity detected by the polarity detecting means and the applied polarity to the signal transmission line match, and the power is restored before the time counting by the timer means ends. When the power is turned on, the polarity is switched so that the polarity stored in the storage means coincides with the polarity applied to the signal transmission line. And switch to the polarity stored in the storage means, and if it lasts until the end of the time count, It is determined that the power supply device can be smoothly restarted in the event of a short-term power failure such as an instantaneous power failure by determining that the power supply device has been disconnected from the transmission line and matching the polarity detected by the polarity detection unit. effective.

According to a fourth aspect of the present invention, a plurality of signal transmission devices and one or more power supply devices are connected by a signal transmission line, and a direct current is applied from the power supply device to the signal transmission lines to supply power to each signal transmission device. And a power supply for supplying alternating current, and a power supply for detecting a polarity of the alternating current supplied from the power supply. Polarity detection means, polarity detection means for detecting the polarity of the signal transmission path, and power supply from the power supply means to the signal transmission path when the polarity detected by the power supply polarity detection means matches the polarity detected by the polarity detection means. Is provided, there is an effect that when connecting the power supply device to the signal transmission line, the trouble of matching the polarities is not required, and the connection can be easily performed.

According to a fifth aspect of the present invention, the power supply polarity detecting means comprises:
Since there is provided a rectifying element for half-wave rectifying the alternating current supplied from the power supply means and a capacitance element charged through the rectification element, the configuration of the power supply polarity detecting means can be simplified. .

[Brief description of the drawings]

FIG. 1 is a block diagram of a signal transmission system including a power supply device according to a first embodiment.

FIG. 2 is a specific circuit diagram of a polarity detection unit in Embodiment 1;

FIG. 3 is a schematic circuit diagram showing another configuration of the above.

FIG. 4 is a block diagram showing a second embodiment.

FIG. 5 is a block diagram showing a third embodiment.

FIG. 6 is a schematic circuit diagram of the above.

FIG. 7 is an explanatory diagram for explaining the above operation.

FIG. 8 shows a conventional signal transmission system, in which the power supply device is 1
It is a block diagram in case of a stand.

FIG. 9 shows a conventional signal transmission system, and is a block diagram when a plurality of power supply devices are provided.

FIG. 10 is a block diagram showing another conventional signal transmission system.

FIG. 11 is a block diagram showing still another conventional signal transmission system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 power supply device 2 power supply unit 3 choke coil 4 polarity detection unit 5 polarity switching unit 6 control circuit unit 10 signal transmission device 20 signal transmission line

Claims (5)

[Claims] 1. A plurality of signal transmission devices and one or more power supply devices are connected by a signal transmission line, and a direct current is applied from the power supply device to the signal transmission line to supply power to each signal transmission device and to perform signal transmission. A power supply device of a signal transmission system that performs signal transmission between each signal transmission device through a path, and a polarity detection unit that detects a polarity of the signal transmission line, and a polarity detection unit that matches a polarity detected by the polarity detection unit. A power supply device for a signal transmission system, comprising: a polarity switching unit that switches a polarity applied to a signal transmission path. 2. The power supply device for a signal transmission system according to claim 1, wherein the polarity detection means includes a switch element that is turned on / off in accordance with the polarity of the signal transmission path. 3. A system comprising: timer means for performing a predetermined time count at the time of a power failure; and non-volatile storage means for storing the polarity of a signal transmission path before time counting by the timer means is started. When the power is restored after the time counting by the timer means is completed, the polarity is switched so that the polarity detected by the polarity detecting means and the applied polarity to the signal transmission line match, and the power is restored before the time counting by the timer means is completed. 3. The power supply device for a signal transmission system according to claim 1, wherein the polarity is switched so that the polarity stored in the storage unit and the polarity applied to the signal transmission line match in the case. 4. A plurality of signal transmission devices and one or more power supply devices are connected by a signal transmission line, and a direct current is applied from the power supply device to the signal transmission line to supply power to each signal transmission device and to perform signal transmission. A power supply device for a signal transmission system that performs signal transmission between each signal transmission device via a path, a power supply unit that supplies an AC, and a power supply polarity detection unit that detects a polarity of the AC supplied from the power supply unit, Polarity detecting means for detecting the polarity of the signal transmission path, and control means for supplying power from the power supply means to the signal transmission path when the polarity detected by the power supply polarity detecting means matches the polarity detected by the polarity detecting means. A power supply device for a signal transmission system, comprising: 5. The power supply polarity detecting means includes a rectifying element for half-wave rectifying an alternating current supplied from the power supply means, and a capacitance element charged via the rectifying element. A power supply device for the signal transmission system according to claim 1.