Electric power supply system

Abstract

To provide an electric power supply system for supplying electric power to external auxiliary equipment.SOLUTION: An electric power supply system comprises: a limit switch which is installed on a target object within a plant, and switches between an ON state and an OFF state depending on the state of the target object; an electric power source device which includes a current detection circuit detecting the ON and OFF states of the limit switch; and an electric power source adapter device which is inserted into wiring between the electric power source device and the limit switch. The electric power source adapter device can be connected to external auxiliary equipment, and supplies electric power based on the current flowing from the electric power source device to the limit switch via a first current path, to the external auxiliary equipment when the external auxiliary equipment is connected and the limit switch is in the ON state, and supplies the electric power based on the current flowing into the electric power source adapter device via a second current path different from the first current path, to the external auxiliary equipment when the limit switch is in the OFF state.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a power supply system. [Background technology]

[0002] Petrochemical plants and other plants often use control valves (i.e. valves) such as ON-OFF valves that are controlled in two positions, fully open and fully closed. Limit switches are installed on control valves to ensure that the fluid control part inside the valve moves to the fully closed or fully open position. The control system is connected to the limit switch via wiring to the site so that the operating status of the valve can be read.

[0003] A technology for monitoring these control valves is disclosed in Patent Document 1. In Patent Document 1, a current detection circuit using a photocoupler detects the current that flows when the contact of the limit switch is on. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-064929 A Summary of the Invention [Problem to be solved by the invention]

[0005] During plant operation, the operating status of the control valve is monitored based on the state of this limit switch. However, it is difficult to predict whether there is an abnormality in the valve's movement based only on information about the control valve's operating status. Therefore, it is desirable to add a preventive maintenance device to the control valve so that valve abnormalities can be detected before the valve breaks down by monitoring the valve's movement. The same can be said not only for valves, but for various objects used in plants. Valves and other objects that can be subject to monitoring are also called objects.

[0006] Preventive maintenance devices are devices that are installed additionally to maintain the objects being monitored (hereafter referred to as external auxiliary devices). By using external auxiliary devices to collect and monitor valve movements in more detail, it is expected that sudden failures that lead to huge losses can be avoided. When adding such external auxiliary devices to existing plant facilities for operation, construction work such as laying cables to supply power is required.

[0007] Therefore, it is conceivable that the installation work can be eliminated by using primary batteries as the power source for the external accessory devices instead of power wiring. However, since batteries have a limited lifespan, maintenance work such as replacement would be necessary, which is not desirable.

[0008] The present invention has been made in consideration of the above, and its object is to provide a power supply system for supplying power to an external accessory device by connecting a power adapter device, without the need to install cables or the like to supply power. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the objective, a power supply system according to an embodiment of the present disclosure includes a limit switch that is provided for an object in a plant and switches between an on state and an off state depending on a state of the object, a power supply device including a current detection circuit that detects the on state and the off state of the limit switch, and a power adapter device that is inserted into a wiring between the power supply device and the limit switch, wherein the power adapter device includes an external connection terminal to which an external accessory device can be connected, and when the external accessory device is connected to the external connection terminal, when the limit switch is in an on state, the power adapter device supplies to the external accessory device power based on a current flowing from the power supply device to the limit switch via a first current path, and when the limit switch is in an off state, supplies to the external accessory device power based on a current flowing into the power adapter device via a second current path different from the first current path.

[0010] It is preferable that the power adapter device includes a voltage-current conversion circuit and a switching circuit, and that the voltage-current conversion circuit does not operate when the limit switch is on, and when the limit switch is off, converts the current flowing through the second current path into power for operating the external accessory device and sends it to the switching circuit, and that when the limit switch is on, the switching circuit supplies the current flowing to the limit switch via the first current path to the external accessory device, and when the limit switch is off, supplies the current converted by the voltage-current conversion circuit to the external accessory device.

[0011] It is preferable that the voltage-current conversion circuit includes an inductor for storing power, and when the limit switch is in an off state, the voltage-current conversion circuit alternates between a state of storing power in the inductor via the second current path and a state of releasing the power stored in the inductor via a third current path different from the second current path.

[0012] It is preferable that the current detection circuit detects the on state of the limit switch based on the current flowing from the power supply device to the power adapter device or the current returning from the power adapter device to the power supply device, and that when the limit switch is in the on state, the current flowing from the power supply device to the power adapter device or the current returning from the power adapter device to the power supply device is equal to or greater than an on determination current that determines in the current detection circuit that the limit switch is in the on state.

[0013] The power adapter device further includes an input control circuit, and the current detection circuit detects the off state of the limit switch based on the current flowing from the power supply device to the power adapter device or the current returning from the power adapter device to the power supply device, and when the limit switch is in the off state, the current flowing from the power supply device to the power adapter device or the current returning from the power adapter device to the power supply device is less than a definite off current that determines in the current detection circuit that the limit switch is in the off state, and it is preferable that the resistance value of the input control circuit is such that when the limit switch is in the off state, a current less than a definite off current that determines in the current detection circuit that the limit switch is in the off state flows.

[0014] Preferably, the external accessory device includes a charging / discharging unit, the charging / discharging unit is charged by power supplied from the power supply device via the power adapter device, and the external accessory device operates by the power supplied from the charging / discharging unit. Note that the object includes a valve for controlling a flow rate of a fluid, and the state of the object includes an open state and a closed state of the valve. Effect of the Invention

[0015] According to the present invention, by connecting a power adapter device, it is possible to supply power from the power supply device for the limit switch to an external accessory device without the need for laying cables or the like for supplying power. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing the connection relationship between a power supply device and a limit switch before a power adapter device is attached. [Diagram 2] FIG. 2 is a block diagram showing the functions of a power supply system including a power adapter device. [Diagram 3] FIG. 3 is a block diagram illustrating an embodiment of a power supply system of the present disclosure. [Figure 4]FIG. 4 is a diagram showing a more specific configuration example of the power supply system of the present embodiment. [Diagram 5] FIG. 5 is a diagram showing a more specific configuration example of the embodiment of the power supply system of the present disclosure. [Figure 6] FIG. 6 is a diagram showing a more specific configuration example of the embodiment of the power supply system of the present disclosure. [Figure 7] FIG. 7 is a diagram showing the relationship between the terminal voltage and the terminal current of the power supply terminal when the power adaptor device is not inserted. [Figure 8] FIG. 8 is a diagram showing the relationship between the terminal voltage and the terminal current between the power supply terminals when the power adapter device is inserted between the limit switch and the power supply device and the limit switch is in the ON state. [Figure 9] FIG. 9 is a simplified circuit diagram showing the first current path when the limit switch is in the on state. [Figure 10] FIG. 10 is a diagram illustrating the power that can be extracted when the limit switch is in the on state. [Figure 11] FIG. 11 is a diagram showing the relationship between the terminal voltage and the terminal current of the power supply terminal when the limit switch is in the off state with the power adapter device inserted. [Figure 12] FIG. 12 is a diagram showing the input control circuit and its peripheral circuits when the limit switch is in the OFF state. [Figure 13] FIG. 13 is a diagram illustrating the power that can be extracted when the limit switch is in the OFF state. [Figure 14] FIG. 14 is a diagram showing the relationship between power before and after conversion by the voltage-current conversion circuit of the power adaptor device when the limit switch is in the OFF state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description of each embodiment, the same or equivalent components between the drawings will be given the same reference numerals, and their description will be simplified or omitted. The present invention is not limited to the disclosed embodiments. In addition, the components of the disclosed embodiments include those that are replaceable and easy for a person skilled in the art, or those that are substantially the same. The configurations described below can be appropriately combined. In addition, the configurations can be omitted, replaced, or modified within the scope of the gist of the invention.

[0018] In this specification, in order to facilitate understanding of the contents of the present disclosure, before describing the present embodiment, a technical background of a plant in which the present power supply system is installed will be described first.

[0019] Large production facilities such as petrochemical plants can operate for nearly 100 years to produce materials essential to life. In response to modern demands, facilities that have been in operation for many years often have additional instrumentation equipment installed on-site to improve safety, quality, and production efficiency. However, installing power wiring for the additional equipment requires the equipment to be shut down, which not only incurs construction costs but also has a significant impact on the operation of the production facility.

[0020] (Connection Relationship) Fig. 1 is a diagram showing the connection relationship between a power supply device and a limit switch SW before a power adapter device is attached. Fig. 1 shows the connection relationship between a limit switch SW and a power supply device 1 before a power adapter device (to be described later) is connected.

[0021] In Fig. 1, a power supply device 1 supplies power to each part in a plant. The power supply device 1 has a DC power supply 11, a current detection circuit 12, and a protection circuit 13. A limit switch SW is connected to the power supply device 1 via wiring L1 and L2. The limit switch SW is provided corresponding to a valve 3, which is an object.

[0022] An example of the object is a valve that controls the flow rate of a fluid. In this case, the state of the object includes the open state and the closed state of the valve. The valve may have any structure such as a ball valve, a butterfly valve, a gate valve, etc. For example, a limit switch SW is in an on state when the valve is in an open state, and in an off state when the valve is in a closed state. However, conversely, the limit switch SW may be in an on state when the valve is in a closed state, and in an off state when the valve is in an open state.

[0023] The object may be a valve that controls the flow of a fluid in two positions, fully open (i.e., open state) and fully closed (i.e., closed state), or a valve that controls the flow of a fluid in a series of positions from fully open to fully closed. The object is not limited to a valve. The object may include various objects that are installed in a plant and whose state may change. An example of an object other than a valve is a damper for adjusting the amount of gas passing through a duct, which is an air passage. However, unless otherwise specified, the object will be described below as a valve. To the extent that there is no contradiction, a valve may be appropriately interpreted as an object.

[0024] A DC current I output from a DC power supply 11 passes through a current detection circuit 12 and a protection circuit 13, and is input to a limit switch SW via a wire L1. If the limit switch SW is in an on state, the DC current I output from the power supply device 1 passes through the wire L1, the limit switch SW, and the wire L2 in this order, and returns to the power supply device 1.

[0025] The current detection circuit 12 is a circuit that detects (senses) the current flowing from the power supply device 1 toward the limit switch SW. In this example, the current detection circuit 12 is provided between the positive side of the DC power supply 11 and the limit switch SW. Note that the current detection circuit 12 may be provided between the limit switch SW and the negative side of the DC power supply 11. In that case, the current detection circuit 12 detects the current returning to the power supply device 1 from the limit switch SW.

[0026] Here, the current value flowing through the wirings L1 and L2 from the power supply device 1 differs between when the limit switch SW is in the off state and when the limit switch SW is in the on state. The current detection circuit 12 has a predetermined current judgment threshold. If the current detection circuit 12 detects a current value equal to or greater than the judgment threshold, it judges that the limit switch SW is in the on state. On the other hand, if the current value is less than the judgment threshold, the current detection circuit 12 judges that the limit switch SW is in the off state. That is, the current detection circuit 12 detects that the limit switch SW is in the on state based on the current flowing from the DC power supply 11 to the limit switch SW. As described above, the limit switch SW is in the on state when the valve 3 is in the fully open state, and is in the off state when the valve 3 is in the fully closed state. The limit switch SW may be in the on state when the valve 3 is in the fully closed state, and be in the off state when the valve 3 is in the fully open state. Therefore, the current detection circuit 12 of the power supply device 1 can detect the open / closed state of the valve 3. The current returning from the limit switch SW to the power supply device 1 through the wiring L2 is a signal for the current detection circuit 12 to detect the state of the limit switch SW. In Fig. 1, this signal is denoted by the symbol "ST" (hereinafter, referred to as signal ST). The signal ST can be said to be a signal that indicates the state of the limit switch SW.

[0027] The protection circuit 13 is a circuit that prevents an excessive current from flowing from the power supply device 1 to the limit switch SW. The protection circuit 13 includes, for example, a resistor that is connected in series to a wire extending from the power supply device 1 to the limit switch SW.

[0028] As described above, power is supplied to the limit switch SW from the power supply device 1 that is originally installed in a production facility such as a plant. Therefore, if a power adapter device that uses this power is installed on this power supply line, it is possible to extract power from the power supply device 1 without preparing a new power source. In other words, if a power adapter device is installed on the wiring L1 and L2, it is possible to extract power from the current flowing from the power supply device 1 toward the limit switch SW.

[0029] (Outline of the power supply system) Next, an overview of a power supply system 100 according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the functions of the power supply system 100 including a power adapter. Fig. 2 shows a configuration in which a power adapter 2 is added to the connection relationship between the limit switch SW and the power supply device 1 described with reference to Fig. 1. An external accessory device 4 is connected to the power adapter 2. The power supply system 100 supplies power to the external accessory device 4 via the power adapter 2.

[0030] The power adapter device 2 supplies an operating current I' to the external accessory device 4 based on the DC current I input from the power supply device 1. The external accessory device 4 is an additional device provided to detect the state of a control valve, for example. The power adapter device 2 extracts a part of the DC current I supplied from the power supply device 1 and supplies it as an operating current I' to the external accessory device 4. The external accessory device 4 operates using the operating current I'.

[0031] The power adapter 2 supplies an operating current I'' to the limit switch SW. Furthermore, the power supply 1 detects a signal ST indicating the state of the limit switch SW via the power adapter 2, and sends this to the power supply 1 as information ST' indicating the state of the limit switch SW. This allows the power supply 1 to detect the open / closed state of the valve 3 (see Figure 1). Therefore, even if the power adapter 2 is inserted, it does not affect the operation and function of the power supply 1 and the limit switch SW.

[0032] (Embodiment) 3 is a block diagram showing an embodiment of a power supply system according to the present disclosure, in which a power supply system 100 includes a power supply device 1, a power adapter device 2, and a limit switch SW.

[0033] The power supply device 1 has a terminal T11 and a terminal T12. The power adapter device 2 has a terminal T13, a terminal T14, a terminal T15, a terminal T16, a terminal T21, and a terminal T22. The terminal T13 is connected to the terminal T11. The terminal T14 is connected to the terminal T12. The terminals T15 and T16 are connected to the terminals of the limit switch SW.

[0034] An external accessory device 4 can be connected to the power adapter device 2. The external accessory device 4 has a terminal T41 and a terminal T42. When the external accessory device 4 is connected to the power adapter device 2, the terminal T41 is connected to the terminal T21, and the terminal T42 is connected to the terminal T22.

[0035] The power supply device 1 includes a protection circuit 13 and a current detection circuit 12. The power adapter device 2 includes an input control circuit 22, a voltage-current conversion circuit 23, and a switching circuit 24. The switching circuit 24 includes a bypass circuit 240. The switching circuit 24 is connected to a terminal T42 of the external accessory device 4 via a terminal T22.

[0036] (Switching circuit) The bypass circuit 240 in the switching circuit 24 has a Zener diode Dz2. This Zener diode Dz2 is connected in parallel to the external accessory device 4. By being connected in parallel, the voltage applied to the external accessory device 4 becomes equal to the voltage applied to the Zener diode Dz2.

[0037] When the external accessory device 4 is not connected, the current corresponding to the signal ST returns to the power supply device 1 through the bypass circuit 240. In other words, when the external accessory device 4 is not connected and the limit switch SW is in the on state, the switching circuit 24 sends the signal ST, i.e., the current flowing through the limit switch SW, to the power supply device 1.

[0038] If the external accessory device 4 is not connected and the limit switch SW is in the off state, the current passes through the Zener diode Dz2. This current passes through the bypass circuit 240. That is, if the external accessory device 4 is not connected and the limit switch SW is in the off state, the switching circuit 24 sends the current converted by the voltage-current conversion circuit 23 to the power supply device 1.

[0039] When the external accessory device 4 is connected, a current flows through the external accessory device 4, and no current flows through the bypass circuit 240. However, when the external accessory device 4 is not operating, for example when the power supply of the external accessory device 4 is off, no current flows through the external accessory device 4. In this case, a current flows through the bypass circuit 240 of the switching circuit 24.

[0040] When the limit switch SW is in the on state, the current supplied from the power supply device 1 does not flow to the voltage-current conversion circuit 23 but flows to the limit switch SW. The power adapter device 2 takes in the current returning from the limit switch SW and supplies this current to the external accessory device 4 via the switching circuit 24.

[0041] When the limit switch SW is in the OFF state, the current supplied from the power supply device 1 does not flow to the limit switch SW, but flows to the voltage-current conversion circuit 23.

[0042] As described later, the voltage-current conversion circuit 23 includes a transistor and an inductor. When the transistor in the voltage-current conversion circuit 23 is on, the voltage-current conversion circuit 23 stores power based on the current taken in in an internal inductor. When the transistor in the voltage-current conversion circuit 23 is off, the voltage-current conversion circuit 23 releases the power stored in the inductor as a current, and the flowing current is supplied as power to the external accessory device 4 via the switching circuit 24. The voltage-current conversion circuit 23 converts the voltage and current under a constant power source so that the voltage required for the operation of the external accessory device 4 is obtained. The on-off operation of the transistor in the voltage-current conversion circuit 23 is, for example, 100 kHz or more.

[0043] When power is being supplied to the external accessory device 4, the current detection circuit 12 in the power supply device 1 must also be operated at the same time. When the limit switch SW is in the on state, a current flows that is determined by the voltage applied to the bypass circuit 240 in the switching circuit 24 in the power adapter device 2, specifically the Zener diode described below, the resistance in the current detection circuit 12, and the voltage of the DC power supply 11. The current value of this current must be equal to or greater than the on-confirmed current at which the current detection circuit 12 identifies that the limit switch SW is in the on state.

[0044] On the other hand, when the limit switch SW is in the off state, a current flows that is determined by the voltage applied to the input control circuit 22 of the power adapter device 2, the resistance value of the current detection circuit 12, and the voltage of the DC power supply 11. The current value of this current needs to be equal to or less than the off-state current at which the current detection circuit 12 identifies that the limit switch SW is in the off state.

[0045] (Specific examples) Hereinafter, an embodiment of the power supply system of the present disclosure will be described with a specific configuration example. Here, the flow of current in the on state and the off state of the limit switch SW will be described. FIG. 4 is a diagram showing a more specific configuration example of the power supply system of this embodiment. FIG. 4 is a diagram showing a current path when the limit switch SW is in the on state. As shown in FIG. 4, when the limit switch SW is in the on state, the current flowing from the power supply device 1 to the power adapter device 2 flows in the direction of the arrows Y11 and Y12, passes through the limit switch SW, and flows in the direction of the arrows Y13 and Y14 into the external accessory device 4. Furthermore, the current flowing into the external accessory device 4 passes through the external accessory device 4 as shown by the arrow Y15, and flows in the direction of the arrows Y16 and Y17 to return to the power supply device 1. The current path from the arrow Y11 to the arrow Y17 is called the first current path.

[0046] The power adaptor device 2 includes an input control circuit 22, a voltage-current conversion circuit 23, and a switching circuit 24. The input control circuit 22 includes resistors R1, R2, and R3, and a Zener diode Dz1. The voltage-current conversion circuit 23 includes a switching regulator 211, diodes D1 and D2, and an inductor L.

[0047] The resistors R1 and R2 of the input control circuit 22 form a voltage dividing resistor circuit. The input control circuit 22 outputs a voltage value corresponding to the ratio of the resistance value of the resistor R2 to the total value of the resistance values ​​of the resistors R1 and R2 from the connection point between the resistors R1 and R2. The input control circuit 22 also generates a constant reference voltage based on the resistance value of the resistor R3 and the Zener voltage of the Zener diode Dz1.

[0048] The switching regulator 211 includes a comparator 211A, a drive circuit (DRV) 211B, and a transistor Tr1. The switching regulator 211 includes a feedback terminal FB, an output terminal OUT, and a ground terminal G. The ground terminal G is electrically connected to the negative side of the DC power supply 11. The feedback terminal FB corresponds to the positive terminal (+) and the negative terminal (-) of the comparator 211A.

[0049] A reference voltage determined by the Zener voltage of the Zener diode Dz1 and a resistor R3 is input to a negative terminal (-) of the comparator 211A. A voltage value divided by resistors R1 and R2 is input to a positive terminal (+) of the comparator 211A.

[0050] The drive circuit 211B is operated by the output voltage of the comparator 211A to operate the transistor Tr1. When the transistor Tr1 is in an ON state, a current based on the output of the drive circuit 211B is output from the output terminal OUT.

[0051] One end of an inductor L is connected to the output terminal OUT. The other end of the inductor L is connected to the anode of a diode D1. The cathode of the diode D1 is connected to a terminal T42 of the external accessory device 4 via a terminal T22. In addition, the output terminal OUT is connected to the cathode of a diode D2. The anode of the diode D2 is connected to a terminal T41 of the external accessory device 4 via a terminal T21.

[0052] (Connection to external accessories) The power adapter device 2 has a terminal T21 and a terminal T22. The terminal T21 is electrically connected to a terminal T41 of the external accessory device 4. The terminal T22 is electrically connected to a terminal T42 of the external accessory device 4. Power is supplied from the power adapter device 2 to the external accessory device 4 via the terminals T21 and T41, and the terminals T22 and T42.

[0053] The terminals T21 and T41 are detachable, and the terminals T22 and T42 are detachable. Therefore, the external accessory device 4 can be removed from the power adapter device 2. Even when the external accessory device 4 is removed, the power adapter device 2 can still operate.

[0054] When the limit switch SW is in the on state, the voltage-current conversion circuit 23 does not operate. When the limit switch SW is in the on state, the terminals T15 and T16 are short-circuited, and a current flows through the limit switch SW but does not flow through the voltage-current conversion circuit 23. The voltage applied to the voltage-current conversion circuit 23 falls below a reference voltage predetermined by the comparator 211A.

[0055] The comparator 211A compares the voltage applied to the positive terminal (+) with the voltage applied to the negative terminal (-). When the voltage applied to the positive terminal (+) is higher than the voltage applied to the negative terminal (-), the comparator 211A sends a Hi signal to the drive circuit 211B. This turns on the transistor Tr1, causing a current to flow from the output terminal OUT.

[0056] On the other hand, when the voltage applied to the positive terminal (+) is lower than the voltage applied to the negative terminal (-), the comparator 211A sends a Low signal to the drive circuit 211B. This turns off the transistor Tr1, and no current flows from the output terminal OUT. When the limit switch SW is in the ON state, the voltage falls below the voltage at the negative terminal (-) of the comparator 211A, and the switching regulator 211 stops operating. The current flowing from the limit switch SW through the first current path returns to the power supply device 1 through the external accessory device 4.

[0057] On the other hand, when the limit switch SW is in the off state, no current flows through the limit switch SW, but flows through the voltage-current conversion circuit 23. Fig. 5 is a diagram showing a more specific configuration example of the embodiment of the power supply system of the present disclosure. Fig. 5 is a diagram showing a path of a current when the limit switch SW is in the off state.

[0058] As shown in FIG. 5, when the limit switch SW is in the off state, the current flowing from the power supply device 1 to the power adapter device 2 flows as indicated by the arrows Y21 and Y22 and flows into the voltage-current conversion circuit 23. If the transistor Tr1 of the switching regulator 211 of the voltage-current conversion circuit 23 is on, the current flows in the directions of the arrows Y23, Y24, and Y25 and flows into the external accessory device 4. That is, when the limit switch SW is in the off state, the current converted by the voltage-current conversion circuit 23 is supplied to the external accessory device 4. Furthermore, the current flowing into the external accessory device 4 passes through the external accessory device 4 as indicated by the arrow Y26, flows in the directions of the arrows Y27 and Y28, and returns to the power supply device 1. The current path from the arrow Y21 to the arrow Y28 is called the second current path. In the case of the second current path, the power adapter device 2 stores the power to be supplied to the external accessory device 4 in the inductor L and supplies the stored power to the external accessory device 4.

[0059] Fig. 6 is a diagram showing a more specific configuration example of the embodiment of the power supply system of the present disclosure, showing a current path when the limit switch SW is in the off state.

[0060] As shown in FIG. 6, when the limit switch SW is in the off state and the transistor Tr1 of the switching regulator 211 of the voltage-current conversion circuit 23 is off, the power stored in the inductor L is discharged as a current as indicated by the arrow Y31. This current passes through the diode D1 and flows in the directions of the arrows Y32 and Y33 to the external accessory device 4. That is, when the limit switch SW is in the off state, the power stored in the inductor L is supplied to the external accessory device 4. Furthermore, the current that has flowed into the external accessory device 4 passes through the external accessory device 4 as indicated by the arrow Y34, flows in the directions of the arrows Y35, Y36, and Y37, and returns to the inductor L through the diode D2. The current path from the arrow Y31 to the arrow Y37 is called the third current path. In the case of the third current path, the power adapter device 2 is in a state in which it discharges the power stored in the inductor L and supplies it as a current to the external accessory device 4.

[0061] When the limit switch SW is in the off state, the current flowing through the voltage-current conversion circuit 23 alternates between the second current path and the third current path. That is, the current flow alternates between a state in which power is stored in the inductor L via the second current path and supplied to the external accessory device 4, and a state in which the power stored in the inductor L is released via the third current path and supplied to the external accessory device 4.

[0062] The operation of the power adaptor 2 will be described in more detail below with reference to FIGS.

[0063] In the switching regulator 211, the comparator 211A compares the voltage applied to the positive terminal (+) with the voltage applied to the negative terminal (-). When the voltage applied to the positive terminal (+) is higher than the voltage applied to the negative terminal (-), the comparator 211A sends a Hi signal to the drive circuit 211B, and the transistor Tr1 turns on. When the transistor Tr1 turns on, a current is output from the output terminal OUT.

[0064] On the other hand, when the voltage applied to the positive terminal (+) of the comparator 211A is lower than the voltage applied to the negative terminal (-), the comparator 211A sends a Low signal to the drive circuit 211B and turns off the transistor Tr1. When the transistor Tr1 turns off, no current is output from the output terminal OUT.

[0065] That is, the drive circuit 211B operates according to the output voltage of the comparator 211A to turn the transistor Tr1 on or off. The switching regulator 211 turns the transistor Tr1 on and off to adjust the current output from the output terminal OUT so that the voltage at the positive terminal (+) of the comparator 211A becomes equal to the reference voltage input to the negative terminal (-) of the comparator 211A.

[0066] Here, it is assumed that the transistor Tr1 is on and a current flows through the second current path. At that time, while power is stored in the inductor L, a current also flows through the external accessory device 4. When a current flows through the second current path, the voltage between the terminals T13 and T14, which is equal to the voltage between the terminals T11 and T12 of the power supply device 1, drops due to the resistance of the power adapter device 2, that is, the terminal voltage of the power adapter device 2. Then, with the drop in the terminal voltage, the voltage divided by the resistors R1 and R2, which is the voltage applied to the positive terminal (+) of the comparator 211A, drops. Since this voltage becomes lower than the reference voltage applied to the negative terminal (-) of the comparator 211A, the output of the drive circuit 211B becomes a Low signal, the transistor Tr1 is turned off, and the current through the second current path stops flowing. When the current through the second current path stops flowing, the power stored in the inductor L is released as a current and is supplied to the external accessory device 4 through the third current path.

[0067] Since no current flows through the second current path in the transistor Tr1, the terminal voltage of the power adapter device 2 rises. When the terminal voltage rises, the voltage divided by the resistors R1 and R2, which is the voltage applied to the positive terminal (+) of the comparator 211A, rises and becomes greater than the reference voltage applied to the negative terminal of the comparator, so that the output of the drive circuit 211B becomes a Hi signal, the transistor Tr1 turns on, and a current flows through the second current path. In this way, when the limit switch SW is in the off state, the voltage-current conversion circuit 23 repeatedly stores power in the inductor L through the second current path and releases the power stored in the inductor L through a third current path different from the second current path.

[0068] Next, the operation of storing power in the inductor L and the operation of releasing the stored power will be described. One end of the inductor L is connected to the output terminal OUT. As shown in FIG. 5, when the transistor Tr1 is on and a current flows through the second current path, the inductor L stores electric energy. When the external accessory device 4 is connected to the power adapter device 2, power is supplied to the external accessory device 4. The switching circuit 24 has a Zener diode Dz2. The Zener diode Dz2 and the external accessory device 4 are connected in parallel. This switching circuit 24 is a so-called shunt regulator, and the same voltage as the voltage applied to the Zener diode Dz2 is applied to the external accessory device 4. When the limit switch SW is in the on state, the switching circuit 24 supplies the current flowing through the limit switch SW by the first current path to the external accessory device 4. When the limit switch SW is in the off state, the switching circuit 24 supplies the current converted by the voltage-current conversion circuit 23 to the external accessory device 4.

[0069] Diodes D1 and D2 are connected to the inductor L. The diodes D1 and D2 are provided to prevent a reverse current flow. The anode of the diode D1 is connected to the other end of the inductor L. The cathode of the diode D1 is connected to the terminal T42 of the external accessory device 4 via the terminal T22. The cathode of the diode D2 is connected to the output terminal OUT. The anode of the diode D2 is connected to the terminal T41 of the external accessory device 4 via the terminal T21.

[0070] 6, when the transistor Tr1 is off, the current discharged from the inductor L flows through the diode D1 to the switching circuit 24, passes through the external accessory device 4, passes through the diode D2, and returns to the inductor L. In other words, the current discharged from the inductor L flows through the third current path.

[0071] At this time, voltage-current conversion is performed under a constant power condition. That is, voltage-current conversion is performed to convert power, which is the product of the current of the second current path when the transistor Tr1 is on and the terminal voltage of the terminals T11 and T12 of the power supply device 1 corresponding to the second current path, into a current whose value is obtained by dividing the power by the voltage applied to the Zener diode Dz2.

[0072] The Zener diode Dz2 of the bypass circuit 240 passes the current when the external accessory 4 is not connected. When the limit switch SW is in the on state, if the external accessory 4 is not connected, the current flows along the first current path from the arrow Y11 to the arrow Y13 shown in FIG. 4, and then passes through the Zener diode Dz2 and flows in the direction of the arrow Y17. At this time, the current passes through the bypass circuit 240 and returns to the DC power source 11. If the external accessory 4 is not connected and the limit switch SW is in the off state, the current passes through the Zener diode Dz2. That is, the current passes through the bypass circuit 240.

[0073] The bypass circuit 240 also includes a Zener diode Dz2 and a capacitor C. In the bypass circuit 240, the capacitor C is connected in parallel to the Zener diode Dz2.

[0074] So far, we have explained the operation of power supply voltage conversion by the power adapter 2. Even if the power adapter 2 is inserted between the power supply 1 and the limit switch SW, the current detection circuit 12 needs to detect the on / off state of the limit switch SW. The input control circuit 22 has a function of adjusting the operation of the voltage-current conversion circuit 23, and at the same time, a function of adjusting the operation of the current detection circuit 12 that detects the on / off state of the limit switch SW. Hereinafter, we will explain the conditions necessary to detect the on / off state of the limit switch SW.

[0075] (Operation without power adapter device) First, the operation when the power adaptor device 2 is not used will be described.

[0076] The characteristics of the current detection circuit 12 are determined in advance regardless of whether the power adapter device 2 is inserted or not. Specifically, the resistance value of the resistor of the current detection circuit 12 in the power supply device 1, the magnitude of the OFF-definition current Ioff that determines that the limit switch SW is in the OFF state, the magnitude of the ON-definition current Ion that determines that the limit switch SW is in the ON state, and the magnitude of the voltage Vd of the DC power supply 11 of the power supply device 1 are determined in advance.

[0077] Hereinafter, it is assumed that the protection circuit 13 and the current detection circuit 12 in the power supply device 1 can be approximated by resistance characteristics in which the voltage and the current are in a proportional relationship.

[0078] 7 is a diagram showing the relationship between the inter-terminal voltage and inter-terminal current of the power supply terminals T1, T2 when the power adapter device 2 is not inserted. In Fig. 7, the vertical axis represents the inter-terminal voltage between the terminals T11, T12 of the power supply device 1, the horizontal axis represents the inter-terminal current between the terminals T11, T12 of the power supply device 1, and the solid line J1 represents the characteristics between the terminals T11, T12 of the power supply device 1.

[0079] The current Ioff in Fig. 7 is a current that determines that the limit switch SW is in the off state (hereinafter referred to as the off-determined current Ioff). The area to the left of the off-determined current Ioff in Fig. 7 is the area in which the limit switch SW is considered to be in the off state.

[0080] The current Ion in Fig. 7 is a current that determines that the limit switch SW is in the on state (hereinafter referred to as the on-determined current Ion). The area to the right of the on-determined current Ion in Fig. 7 is the area in which the limit switch SW is considered to be in the on state.

[0081] Even when the power adapter device 2 is inserted, it is necessary that the current flowing is within the range regarded as the on state or off state.

[0082] In Figure 7, point OFF1 indicates that no current is flowing, and therefore the limit switch SW is in the off state. At this time, the voltage between the terminals is at its maximum value, and the current between the terminals is at its minimum value (0). Point ON1 indicates that the limit switch SW is in the on state. At this time, the voltage between the terminals is at its minimum value (0), and the current between the terminals is at its maximum value. In this way, the voltage between the power supply terminals T1 and T2 is at its maximum value when the limit switch SW is in the off state, and the more current flows, the lower it becomes.

[0083] (Operates when using power adapter device) Next, we will explain the power of operation when using the power adapter 2. Fig. 8 is a diagram showing the relationship between the terminal voltage and terminal current between the power terminals T1, T2 when the power adapter 2 is inserted between the limit switch SW and the power supply 1 and the limit switch SW is in the on state.

[0084] When the limit switch SW is in the on state using the power adapter 2, part of the power is consumed by the circuit in the power adapter 2. Therefore, when the limit switch SW is in the on state, it is in the state of point ON2 in Fig. 8. The power adapter 2 needs to be designed so that the terminal current and terminal voltage at this point ON2 satisfy the specifications of the current detection circuit 12 of the power supply 1. In other words, when the limit switch SW is in the on state, the terminal current needs to be equal to or greater than the on-definite current Ion.

[0085] 9 is a simplified circuit diagram showing the first current path when the limit switch SW is in the on state. Using FIG. 9, a condition in which the inter-terminal current is equal to or greater than the on-definite current Ion for determining that the current detection circuit 12 is in the on state will be specifically described.

[0086] In FIG. 9, if the voltage of the DC power supply 11 of the power supply device 1 is Vd, the voltage applied to the Zener diode Dz2 in the switching circuit 24 is Vt, and the resistance value of the resistor R12 of the current detection circuit 12 is Rs, the on-definite current Ion can be expressed by the following equation (1). (Vd-Vt) / Rs≧Ion …(1) The Zener voltage of the Zener diode Dz2 needs to be selected so that it becomes the voltage Vt that satisfies the formula (1).

[0087] 10 is a diagram for explaining the power that can be extracted when the limit switch SW is in the on state, in which the horizontal axis represents the current between the terminals of the power supply device 1 and the vertical axis represents the voltage between the terminals of the power supply device 1.

[0088] In Fig. 10, when focusing on point ON2 on solid line J1, the area of ​​hatched range M1 including point ON2 is calculated as the product of terminal voltage and terminal current, and therefore represents power. That is, hatched range M1 shown in Fig. 10 is the power that can be extracted when limit switch SW is in the on state. Hereinafter, for convenience of explanation, range M1 may be referred to as power M1.

[0089] 11 is a diagram showing the relationship between the terminal voltage and terminal current of the power supply terminals T1, T2 when the limit switch SW is in the off state with the power adapter device 2 inserted. In FIG. 11, the horizontal axis represents the terminal current of the power supply device 1, and the vertical axis represents the terminal voltage of the power supply device 1.

[0090] In Fig. 11, because the limit switch SW is in the OFF state, point ON2 (see Fig. 8) on the solid line J1 moves to point OFF2 as indicated by arrow Y4. Point OFF2 indicates that the limit switch SW is in the OFF state. The power adapter 2 must be designed so that the terminal current and terminal voltage satisfy the specifications of the current detection circuit 12 of the power supply 1. In other words, when the limit switch SW is in the OFF state, the current value of the current returning from the power adapter 2 to the power supply 1 must be equal to or less than the off-state current Ioff.

[0091] Fig. 12 is a diagram showing the input control circuit 22 and its peripheral circuits when the limit switch SW is in the off state. In Fig. 12, the resistance value of the resistor R12 of the current detection circuit 12 is indicated as Rs.

[0092] In FIG. 12, when the limit switch SW is in the off state, the voltage-current conversion circuit 23 repeatedly stores power and releases the stored power by turning on and off the transistor Tr1. This causes a high-speed change between a state in which a current flows and a state in which a current does not flow. For this reason, the current flowing through the resistor R12 (resistance value Rs) of the current detection circuit 12 is treated as the average current of these. The resistance value of the input control circuit 22 is set so that the current flowing through the resistor R12 (resistance value Rs) of the current detection circuit 12 is equal to or less than the off-definite current Ioff. More specifically, the resistance values ​​of the resistors R1, R2, and R3 of the input control circuit 22 are set so that the current flowing through the resistor R12 of the current detection circuit 12 is equal to or less than the off-definite current Ioff. Hereinafter, for convenience of explanation, the resistance value of the resistor R1 may be written as "R1" and the resistance value of the resistor R2 may be written as "R2".

[0093] In the input control circuit 22, if the voltage applied to the series circuit of the resistors R1 and R2 is Vx and the voltage applied to the Zener diode Dz1 is Vz, the voltage Vx can be expressed by the following equation (2). Vx = Vz * (R1 + R2) / R2 … (2)

[0094] In addition, in formula (2), "*" indicates multiplication. The same applies to the following explanations.

[0095] The inter-terminal current flowing between terminals T11 and T12 of power supply device 1 must satisfy the relationship expressed by the following equation (3), where Vd is the power supply voltage and Rs is the resistance value of resistor R12 of current detection circuit 12. (Vd-Vx) / Rs =(Vd-Vz*(R1+R2) / R2) / Rs≦Ioff …(3)

[0096] That is, when the limit switch SW is in the OFF state, it is necessary to set the resistance values ​​of the resistors R1 and R2 of the input control circuit 22 so as to satisfy the condition of equation (3) regarding the operation of the voltage-current conversion circuit 23.

[0097] 13 is a diagram for explaining the power that can be extracted when the limit switch SW is in the OFF state, in which the horizontal axis represents the current between the terminals of the power supply device 1 and the vertical axis represents the voltage between the terminals of the power supply device 1.

[0098] In FIG. 13, when focusing on point OFF2 on solid line J1, the area of ​​hatched range M2 including point OFF2 is calculated as the product of terminal voltage and terminal current, and therefore represents power. That is, hatched range M2 shown in FIG. 13 is the power that can be extracted when limit switch SW is in the OFF state. According to range M2 shown in FIG. 13, the terminal voltage is higher than range M1 shown in FIG. 10. Also, according to range M2, the terminal current is lower than range M1 shown in FIG. 10. Hereinafter, for convenience of explanation, range M2 may be referred to as power M2.

[0099] FIG. 14 is a diagram showing the relationship between the power before and after conversion by the voltage-current conversion circuit 23 of the power adaptor device 2 when the limit switch SW is in the OFF state.

[0100] The voltage and current converted under a constant power condition will be described below. The voltage applied to the external accessory device 4 connected to the power adapter device 2 is the voltage Vt applied to the Zener diode Dz2 of the switching circuit 24. Before being converted by the voltage-current conversion circuit 23, the product of the voltage V1 and the current I1 is a value that falls within the range M2. In FIG. 14, the range M2 is a rectangular range whose vertices are the intersection of the vertical and horizontal axes, the point of the terminal-to-terminal voltage V1 on the vertical axis, the point of the terminal-to-terminal current I1 on the horizontal axis, and the point OFF2.

[0101] As described above, the current value increases by converting the voltage to a current. After conversion by the voltage-current conversion circuit 23, the product of the voltage V2 and the current I2 becomes a value that falls within the range M3 including the point OFF3. In FIG. 14, the range M3 is a rectangular range having four vertices: the intersection of the vertical axis and the horizontal axis, the point of the inter-terminal voltage V2 on the vertical axis, the point of the inter-terminal current I2 on the horizontal axis, and the point OFF3. The area of ​​the range M3 is the same as the area of ​​the range M2.

[0102] Below, the first and second examples will be explained together with specific numerical values.

[0103] (Example 1) First, as a first example, when the power adapter device 2 is not inserted, the voltage Vd of the DC power supply 11 of the power supply device 1 is 24 (V), the resistance value Rs of the resistor R12 of the current detection circuit 12 is 4 (kΩ), the confirmed on current Ion of the current detection circuit 12 is 4 (mA), and the confirmed off current Ioff is 3 (mA).

[0104] Here, reference is made again to Fig. 7. In Fig. 7, the voltage at point OFF1 is 24 (V), and the current at point ON1 is 6 (mA).

[0105] Next, let us consider the case where the power adapter device 2 is inserted. The voltage applied to the external accessory device 4, i.e., the voltage Vt applied to the Zener diode Dz2 of the switching circuit 24, is set to 3 (V). When the limit switch SW is in the on state, the current between the terminals of the power supply device 1 can be expressed by equation (4). (Vd-Vt) / Rs =(24-3) / 4000=5.25mA≧Ion=4mA …(4)

[0106] In the above formula (4), the current between the terminals of the power supply device 1 becomes larger than the on-definite current Ion of 4 (mA), and satisfies the condition of formula (1). At this time, the power M1 that can be supplied to the external accessory device 4 can be expressed by formula (5). M1 = 3V * 5.25mA = 15.75mW … (5)

[0107] When the limit switch SW is in the off state, if the voltage Vx applied to the resistors R1 and R2 of the input control circuit 22 is 15 (V), the off-definite current Ioff can be expressed by the formula (6). (Vd-Vx) / Rs =(24-15) / 4000=2.25mA≦Ioff=3mA …(6) In the above formula (6), the current between the terminals of the power supply device 1 is smaller than the off-definite current Ioff of 3 (mA), and therefore satisfies the condition.

[0108] At this time, the power M2 that can be supplied to the external accessory device 4 can be expressed by the formula (7). M2 = 15V * 2.25mA = 33.75mW … (7) It can be seen that power M2 is greater than power M1, and power M2 can be approximately twice as large as power M1. This means that voltage-current conversion circuit 23 can supply more power to external accessory device 4 when limit switch SW is in the OFF state than when limit switch SW is in the ON state. Power M2 corresponds to M2 in FIG. 14.

[0109] Since the voltage applied to the external accessory device 4 is 3 (V), the current that can be passed through the external accessory device 4 can be expressed by equation (8). 33.75 / 3=11.25mA …(8)

[0110] As can be seen from the above formula (8), the current that can be passed through the external accessory device 4 is about 10 (mA). This allows the sensor to be operated and radio waves to be sent and received by short-range wireless communication. Therefore, it can be seen that the current obtained by the power adapter device 2 is sufficient to operate the external accessory device 4.

[0111] (Example 2) Next, as a second example, when the limit switch SW is in the off state and the current flowing through the second current path is the average current due to the on / off of the transistor Tr1, the resistance of the input control circuit 22 when the current detection circuit 12 does not turn it on will be described.

[0112] When the power adapter device 2 is not inserted, the voltage Vd of the DC power supply 11 is 24 (V), and the current between the terminals of the DC power supply 11 when the limit switch SW is in the on state is 5 (mA). In this case, the resistance value Rs of the resistor R12 of the current detection circuit 12 can be expressed by the following equation (9). Rs = 24 V / 5 mA = 4.8 kΩ … (9)

[0113] The voltage between the terminals of DC power supply 11 when the average current between the terminals of DC power supply 11 becomes 2 (mA) when power adapter device 2 is inserted, i.e., the voltage Vx across both ends of resistors R1 and R2 of input control circuit 22, can be expressed by the following equation (10). Vx=24V*(5mA-2mA) / 5mA=14.4V …(10)

[0114] In this case, the power M2 is M2 = 14.4 V * 2 mA = 28.8 mW. Since the voltage applied to the external accessory device 4 is 3 (V), the current flowing to the external accessory device can be expressed by the following equation (11). 28.8mW / 3V=9.6mA …(11) In addition, in this calculation, the current flowing through resistors R1 and R3 is ignored, the self-consumption current of switching regulator 211 is assumed to be zero, and the conversion efficiency of voltage-current conversion circuit 23 consisting of transistor Tr1, inductor L, etc. is assumed to be 100%. Considering these points, the power that can be extracted when limit switch SW is in the off state, in particular, is actually lower than the value expressed by equation (11).

[0115] The reference voltage in the comparator 211A is determined in advance, and each resistance value of the input control circuit 22 is determined so as to be equal to the reference voltage. Specifically, if the voltage Vx applied to the resistors R1 and R2 of the input control circuit 22 is Vx=14.4 (V) and the voltage applied to the Zener diode Dz1 of the input control circuit 22 is Vz, then the resistance values ​​of the resistors R1 and R2 of the input control circuit 22 are determined so as to satisfy the formulas (12) and (13). (Vd-Vx) / Rs=(Vd-Vz*(R1+R2) / R2) / Rs =(24-Vz*(R1+R2) / R2)≦Ioff …(12) (R1+R2) / R2=14.4 / Vz …(13)

[0116] Although the resistance values ​​of resistors R1 and R2 of the input control circuit 22 can be calculated appropriately as described in equations (12) and (13), fine adjustment of the resistance values ​​is performed on-site where the power adapter device 2 is installed. For this reason, it is preferable to use resistors whose resistance values ​​can be adjusted, such as variable resistors, for the resistors of the input control circuit 22. For example, the resistance value Rs of resistor R12 of the current detection circuit 12, the value of the on-definition current Ion of the current detection circuit 12, and the value of the off-definition current Ioff are determined by the specifications of the current detection circuit 12. For this reason, adjustment of each value is performed on-site where the power adapter device 2 is installed.

[0117] (Charge / discharge section) When the external accessory device 4 has a charging / discharging unit 41, the charging / discharging unit 41 is charged by a current output from the voltage / current conversion circuit 23 and input to the external accessory device 4. The charging / discharging unit 41 functions as a power source for the external accessory device 4 by discharging. In other words, the external accessory device 4 includes the charging / discharging unit 41 that is charged by power supplied from the power adapter device 2, and the external accessory device 4 operates using the charging / discharging unit 41 as a power source. The charging / discharging unit 41 is, for example, a secondary battery or a supercapacitor.

[0118] (Current flowing through the switching circuit) As described above, a current flows through the Zener diode Dz2 in the switching circuit 24 when the external accessory device 4 is not connected, and no current flows through the Zener diode Dz2 when the external accessory device 4 is not connected. However, even if the external accessory device 4 is connected, a current flows through the Zener diode Dz2 in the switching circuit 24 when the external accessory device 4 is in an off state and no current flows.

[0119] Regardless of whether the external accessory device 4 is connected, when the capacitor C in the switching circuit 24 is fully charged (i.e., fully charged), no current flows through the capacitor C, and so a current flows through the Zener diode Dz2 in the switching circuit 24. Regardless of whether the external accessory device 4 is connected, when the charge / discharge unit 41 is fully charged (i.e., fully charged), no current flows through the charge / discharge unit 41. In this case, a current flows through the Zener diode Dz2 in the switching circuit 24.

[0120] In other words, whether the limit switch SW is in the on or off state, a voltage that attempts to pass a certain amount of current to the external accessory device 4 is applied to the switching circuit 24. Therefore, when the limit switch SW is in the off state, the external accessory device 4 is in the off state, or the capacitor C is fully charged and no current flows, the voltage applied to the switching circuit 24 rises. If the voltage rises, current flows through the Zener diode Dz2 of the switching circuit 24.

[0121] (others) In the above description, the voltage applied to the external accessory device 4 is the same as the voltage applied to the Zener diode Dz2 of the switching circuit 24. The voltage applied to this Zener diode Dz2 may be set to be, for example, a voltage higher than the voltage applied to the external accessory device 4.

[0122] The external accessory device 4 may be a device that operates when power is supplied, such as a sensor or a wireless device. Alternatively, it may emit light or sound from a warning light when the limit switch SW is turned on, or it may detect the opening of the control valve and transmit the opening data to the maintenance monitoring device wirelessly or the like. For example, it may detect the opening of the control valve and transmit the opening data to the maintenance monitoring device wirelessly or the like. Alternatively, it may further include a camera that captures an image showing the open or closed state of the control valve, and transmit the data of the image captured by this camera. [Explanation of symbols]

[0123] 1 Power supply 2 Power adapter unit 3 Valve 4 External accessories 11 DC power supply 12 Current detection circuit 13 Protection circuit 22 Input control circuit 23 Voltage-to-current conversion circuit 24 Switching circuit 41 Charge / discharge section 100 Power Supply System 211 Switching regulator 211A Comparator 211B Drive circuit C Capacitor D1, D2 Diodes Dz1, Dz2 Zener diode L Inductor L1, L2 wiring SW Limit switch

Claims

1. a limit switch that is provided for an object in a plant and switches between an on state and an off state depending on a state of the object; A power supply device including a current detection circuit that detects the on and off states of the limit switch; a power adapter device inserted into wiring between the power supply device and the limit switch; The power adapter device includes an external connection terminal to which an external accessory device can be connected; When the external accessory device is connected to the external connection terminal, The power adapter device includes: When the limit switch is in an on state, power is supplied to the external accessory device based on a current flowing from the power supply device through a first current path to the limit switch; When the limit switch is in an off state, the power supply system supplies power to the external accessory device based on a current flowing into the power adapter device via a second current path different from the first current path.

2. The power adapter device includes a voltage-current conversion circuit and a switching circuit; The voltage-current conversion circuit includes: When the limit switch is in an on state, no operation is performed; When the limit switch is in an off state, the current flowing through the second current path is converted into power for operating the external accessory device and sent to the switching circuit; The switching circuit includes: When the limit switch is in an on state, a current flowing through the limit switch via the first current path is supplied to the external accessory device; When the limit switch is in an OFF state, the current converted by the voltage-to-current conversion circuit is supplied to the external accessory device. The power supply system according to claim 1 .

3. The voltage-current conversion circuit includes: Includes an inductor to store power, When the limit switch is in an off state, The voltage-current conversion circuit includes: a state in which power is stored in the inductor through the second current path; and releasing the power stored in the inductor through a third current path different from the second current path. The power supply system according to claim 2 .

4. The current detection circuit detects the on state of the limit switch based on a current flowing from the power supply device to the power adapter device or a current flowing from the power adapter device back to the power supply device; When the limit switch is in the on state, the current flowing from the power supply device to the power adapter device or the current flowing from the power adapter device back to the power supply device is equal to or greater than the on-confirmation current that determines in the current detection circuit that the limit switch is in the on state. The power supply system according to claim 1 or 2.

5. The power adapter device further comprises an input control circuit; the current detection circuit detects the off state of the limit switch based on a current flowing from the power supply device to the power adapter device or a current flowing from the power adapter device back to the power supply device; When the limit switch is in an OFF state, a current flowing from the power supply device to the power adapter device or a current flowing from the power adapter device back to the power supply device is equal to or less than an OFF determination current that determines in the current detection circuit that the limit switch is in an OFF state; The resistance value of the input control circuit is a value that allows a current flow that is equal to or less than an off-state determination current that determines that the limit switch is in an off state in the current detection circuit when the limit switch is in an off state. The power supply system according to claim 1 or 2.

6. The external accessory device includes a charge / discharge unit, the charging / discharging unit is charged by power supplied from the power supply device via the power adapter device, The external accessory device is operated by the power supplied from the charge / discharge unit. The power supply system according to claim 1 or 2.

7. the object includes a valve for controlling a flow rate of a fluid; The state of the object includes an open state and a closed state of the valve. The power supply system according to claim 1 or 2.

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