JP2008097423A - Current monitoring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current monitoring device that can be correctly operated even to a circuit part of large current consumption. <P>SOLUTION: The current monitoring device comprises a current detecting part interposed in a transmission line to measure a current value of a signal current; a source voltage generating part interposed in the transmission line to output voltage generated at both ends by allowing the signal current to flow through the transmission line; a storage part connected in parallel to both ends of the source voltage generating part to store a current output from the source voltage generating part; a voltage monitoring part connected to both ends of the storage part to monitor voltage at both ends and to output a control signal when detecting that the voltage exceeds a predetermined voltage value; and a power source control part for connecting the source voltage generating part and the storage part to a predetermined first circuit when the control signal is output from the voltage monitoring part, to operate the circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a current monitor device, and more particularly to a current monitor device that monitors a current flowing in a two-wire industrial current transmission line.

  2. Description of the Related Art Conventionally, chemical plants, petroleum plants, and the like have industrial measuring instruments that are installed for the purpose of measuring physical quantities such as the flow velocity of fluid flowing through pipes in addition to the pressure and temperature of plant components. For example, as shown in FIG. 9, the industrial measuring instrument 1 is measured by being inserted in series with the two-wire transmission line 2 together with the DC power source 3 (for example, DC 24V) and the load resistor 4 (for example, 250Ω). The physical quantity is converted into a current value in the range of 4 to 20 mA and sent to the two-wire transmission line 2.

  Specifically, this type of current loop circuit was measured by outputting 20 mA when the physical quantity measurable by the industrial measuring instrument was 100%, and outputting 4 mA when the physical quantity was 0%. An electric current proportional to the physical quantity is output from the industrial measuring instrument. The load resistance is set to 250Ω because when a current of 4 mA flows through the load resistance, the voltage drop at both ends of the load resistance is 1 V, and when the current of 20 mA flows, the voltage drop is 5 V. This is because voltage values in the range of 1 V to 5 V are convenient for use in various control calculations.

  On the other hand, as this type of industrial measuring instrument, the power source for operating the measuring instrument itself is generated by using the current flowing through the two-wire transmission line, and the measuring instrument operating power supply, power supply wiring, or battery There is known a two-wire transmitter that eliminates the need (see, for example, Patent Document 1). This 2-wire transmitter creates an operating power source inside the transmitter using the current flowing through the 2-wire transmission line, and outputs a current corresponding to the physical quantity measured by the measuring instrument to the 2-wire transmission line. is there.

  Alternatively, the current monitor device may adopt a method of wirelessly transmitting a measurement value detected by the current monitor device, for example, as shown in FIG. This method is configured by providing a wireless monitoring device 5 that measures the current flowing through the two-wire transmission path by the current monitoring device and transmits the measurement data wirelessly. The wireless monitor device 5 includes, for example, a battery 6 as a power source for operating the device.

The inventors have proposed a current monitoring device that eliminates the need for the battery 6 for operating the wireless monitoring device 5 and wirelessly transmits the measured current value (see, for example, Patent Document 2).
This current monitor device outputs a signal current corresponding to the physical quantity measured by the measuring instrument 1 to the two-wire transmission line 2 as shown in the block diagram of FIG. In the transmission line 2, a direct current power source 3 that outputs a direct current of a predetermined voltage (for example, 24V) and a load resistor 4 having a predetermined resistance value (for example, 250Ω) are inserted in series to form a current loop. The measuring instrument 1 converts a physical quantity measured by a sensor (not shown in FIG. 11) into a signal current having a current value of 4 mA to 20 mA, for example, and outputs the signal current to the transmission line 2. The current monitoring device 10 described in Patent Literature 2 is inserted in series in the transmission line 2 of the measurement system configured as described above, and detects a current flowing through the transmission line 2.

  Specifically, the current monitoring device 10 has two terminals VP and VM, and the current flowing through the transmission line 2 by inserting the current monitoring device 10 in series with the transmission line 2 using these terminals VP and VM. A power supply voltage generation unit 20 that generates a predetermined voltage from a current, a current detection unit 30 that detects a current value of a signal current flowing through the transmission line 2, and a wireless that wirelessly transmits a current value (current data) detected by the current detection unit 30 The unit 40 is provided.

  In the current monitoring device configured as described above, in order for the radio unit 40 to operate, a voltage equal to or higher than a predetermined voltage level must be output from the power supply voltage generation unit 20. This point will be described more specifically with reference to a characteristic graph showing an example of the relationship between the power supply voltage applied to the wireless unit 40 of FIG. That is, as the voltage applied to the wireless unit 40 is gradually increased from 0V, the current consumption slightly increases. However, when the voltage is eventually close to 2V, the current consumption increases rapidly, and then consumed in proportion to the power supply voltage. The current increases.

If the minimum operating voltage at which the wireless unit 40 having such characteristics operates is, for example, 2.9V, the current consumed by the wireless unit 40 at this time is 7 mA. Therefore, when the current flowing through the transmission line 2 is 4 mA, the current for operating the radio unit 40 is insufficient.
Therefore, a power storage line C1 such as a capacitor is provided in parallel with the wireless unit 40 in a power supply line (between VSUP and GND) for supplying power to the wireless unit 40, while the wireless unit 40 is operated intermittently. And when the radio | wireless part 40 is dormant, while the energy output from the power supply voltage generation part 20 is stored in the electrical storage part C1, the shortage of the current supplied from the power supply voltage generation part 20 when the radio | wireless part 40 act | operates Is compensated by discharging the electric charge stored in the power storage unit C1 to the radio unit 40 as a current.
JP-A-9-81883 Japanese Patent Application No. 2005-251919

  There are many CPUs whose current consumption decreases when the operation of the CPU is stopped by the reset pin, but there are CPUs whose current consumption does not decrease even when the operation is stopped. Even when the operation is stopped by such a reset pin, the current consumption is not reduced, and when the CPU having the power supply voltage-current consumption characteristic as described above is used, the power storage unit The power storage to C1 stops, and the voltage at both ends of the power storage unit C1, that is, the voltage at both ends of the wireless unit 40 may not reach the voltage necessary to operate the wireless unit 40. In this case, the voltage at both ends of the wireless unit 40 does not reach the voltage necessary for operating the wireless unit 40 forever. For this reason, there has been a problem that the radio unit 40 does not operate any time.

  In view of the above-described circumstances, the inventors provide a current monitoring device that can correctly operate the current monitoring device already proposed for a circuit unit (for example, a wireless unit) that consumes a large amount of current.

In order to achieve the above-described object, the current monitoring device according to the present invention is a current monitoring device that measures a current value that is converted into a signal current by converting a physical quantity measured by a measuring instrument into a signal current,
A current detector that measures the current value of the signal current inserted in the transmission line, and outputs a voltage generated at both ends of the signal current flowing through the transmission line inserted in the transmission line. A power supply voltage generation unit, a power storage unit connected in parallel to both ends of the power supply voltage generation unit to store current output from the power supply voltage generation unit, and a voltage connected to both ends of the power storage unit A voltage monitoring unit that outputs a control signal when it is detected that the voltage exceeds a predetermined voltage value, and the power supply voltage generating unit and the power storage when the control signal is output from the voltage monitoring unit. And a power supply control unit for operating the circuit by connecting the unit to a predetermined first circuit.

In particular, the voltage monitoring unit holds the output of the control signal when detecting that the voltage across the power storage unit exceeds a predetermined voltage value.
Preferably, the voltage monitoring unit holds the output of the control signal when it detects that the voltage across the power storage unit exceeds a predetermined first voltage value, and the voltage across the power storage unit is Stopping the output of the control signal when it is detected that it has fallen below a second voltage value lower than the first voltage value and higher than the minimum voltage required to operate the first circuit. Is desirable.

Further, the current monitoring device is further connected to both ends of the power supply voltage generation unit in parallel to operate, and is inserted between the power supply voltage generation unit and the power storage unit to generate a predetermined current. And a constant current section that flows into the power storage section.
The first circuit is a wireless unit that wirelessly transmits a current value measured by the current detection unit.

  Therefore, when the voltage monitoring unit detects that the voltage across the power storage unit has fallen below the second voltage value, the current monitoring device described above gives a command to the power supply control unit to the first circuit (for example, the radio unit). The current to be supplied is cut off, and the power storage unit is charged until the first voltage value is exceeded. When the voltage monitoring unit detects that the voltage of the power storage unit has exceeded a predetermined voltage, the power supply control unit is instructed to supply current to the first circuit.

  According to the current monitoring device of the present invention, the power supply voltage generation unit inside the current monitoring device uses the current flowing through the transmission line to charge the power storage unit to operate a predetermined circuit (for example, a wireless unit). When the voltage monitoring unit detects that the voltage of the power storage unit that has risen due to charging exceeds a predetermined voltage, the power supply control unit is driven to change the power supply voltage generation unit and the power storage unit to the wireless unit, etc. Since the current is supplied, it can be assured that the radio unit, for example, which consumes a large amount of current, operates correctly.

In particular, when the voltage output from the power supply voltage generator drops, the voltage monitoring unit stops the operation of the power supply control unit before this voltage falls below the minimum operating voltage required for the operation of the wireless unit, etc. Since the current supplied to the predetermined first circuit is cut off, an unstable operation is not caused to the wireless unit or the like due to the voltage drop.
The current monitoring device of the present invention further includes a constant current unit between the power supply voltage generation unit and the power storage unit, and is configured by connecting another circuit (second circuit) in parallel with the power supply voltage generation unit. Since the sum of the current flowing through the constant current section and the second circuit satisfies the current flowing through the transmission line, the power storage section can be charged with a constant current, while the second circuit is always operated. Is also possible.

  Further, the current monitoring device of the present invention measures the current flowing in the transmission line with no power source without using power supply wiring or a battery for operating the current monitoring device if the first circuit is a wireless unit, and the measurement The value can be transmitted wirelessly. Therefore, the current monitoring device of the present invention does not require a power supply wiring and a wired transmission path for transmitting the measured current data, and does not require the cost of laying the power supply wiring and the wired transmission path. In addition to having the property, it is possible to achieve an excellent practical effect that it can be easily applied to existing plants.

  Hereinafter, a current monitoring device according to the present invention will be described with reference to the accompanying drawings. 1 to 8 are diagrams for explaining an example of an embodiment for carrying out the invention, and the present invention is not limited to these drawings. Also, in these drawings, the portions denoted by the same reference numerals as those in FIGS. 9 to 11 represent the same components as the current monitoring device using the two-wire transmission path described above, and the basic configuration is shown in FIGS. This is similar to the conventional one shown.

  FIG. 1 is a schematic configuration diagram of a main part showing a first embodiment of the present invention. In this figure, 1 is equipped with various sensors (not shown in FIG. 1) to measure a physical quantity (for example, pressure, temperature, flow rate, etc.) to be measured and transmits a signal current corresponding to the measured physical quantity in a two-wire manner. This is an industrial measuring instrument (hereinafter sometimes simply referred to as a measuring instrument) that outputs the path 2 (hereinafter also referred to simply as a transmission path). In the transmission line 2, a direct current power source 3 that outputs a direct current of a predetermined voltage (for example, 24V) and a load resistor 4 having a predetermined resistance value (for example, 250Ω) are inserted in series to form a current loop. The measuring instrument 1 converts the physical quantity measured by the sensor into a signal current having a current value of 4 to 20 mA, for example, and outputs the signal current to the transmission line 2. The current monitoring device 10 of the present invention is configured as described above, and detects a current flowing through the transmission line 2 in series with the transmission line 2 of the measurement system.

  The current monitoring device 10 includes two terminals VP and VM that are provided in series with the transmission line 2, and includes a power supply voltage generation unit 20 that generates a predetermined voltage from the current flowing through the transmission line 2. . The power supply voltage generator 20 outputs a predetermined voltage generated between the GND line 11 having a reference potential of 0V and the VSUP line 12 having a positive potential VSUP. A current detection unit 30 that detects the current value of the signal current flowing through the transmission line 2 is inserted in the GND line.

  Between the VSUP line 12 and the GND line 11 on the voltage output side of the power supply voltage generation unit 20, a power storage unit C <b> 1 that stores current output from the power supply voltage generation unit 20 is connected in parallel with the power supply voltage generation unit 20. Has been. At both ends of the power storage unit C1, the voltage monitoring unit 21 that monitors the voltage between the VSUP line 12 and the GND line 11 and the voltage at both ends of the power storage unit monitored by the voltage monitoring unit 21 have reached a predetermined voltage value. When this is detected, a power supply control unit 22 that connects or opens both ends of the power supply voltage generation unit 20 and the power storage unit C1 is connected to the radio unit 40 as a predetermined first circuit.

  Incidentally, the power supply control unit 22 is, for example, a MOSFET inserted in a power supply line that connects the VSUP line 12 and the positive power supply side (wireless unit +) of the wireless unit 40 as shown in FIG. A drain and a source are connected, and a control signal from the voltage monitoring unit 21 is given to the gate. The gate of this MOSFET is connected to the source via a resistor R, and both ends of the radio unit 40, the power supply voltage generation unit 20 and the power storage unit C1 are connected by a negative logic control signal output from the voltage monitoring unit 21 ( ON) or open (OFF).

  Alternatively, the power supply control unit 22 has a MOSFET drain inserted in a power supply line that connects the GND line 11 and the ground side (radio unit −) of the radio unit 40 as shown in FIG. The source may be connected, and the gate may be configured to receive a control signal from the voltage monitoring unit 21. The gate of the MOSFET is connected to the source via the resistor R, and on / off of the power supplied to the wireless unit 40 is controlled by a positive logic control signal output from the voltage monitoring unit 21.

  The operation of the current monitoring device according to the first embodiment of the present invention configured as described above will be described with reference to the graph shown in FIG. In the voltage monitoring unit 21, the voltage across the power storage unit C1 is higher than the minimum operating voltage Vmin at which the radio unit 40 operates, and exceeds a predetermined voltage threshold Vthh that is a voltage sufficient for the radio unit 40 to operate. When it is detected that the voltage has been reached, a control signal (ON command) is given to the power supply control unit 22, and current is supplied to the radio unit 40 from the power supply voltage generation unit 20 and the power storage unit C1.

  Then, the wireless unit 40 starts an initial operation, performs predetermined initialization, and shifts to a dormant state. Thereafter, the radio unit 40 repeats the pause / operation at a predetermined cycle (for example, every 1 second). At this time, when the wireless unit 40 is in a dormant state, the power storage unit C1 is charged by the current output from the power supply voltage generating unit 20, and the voltage at both ends gradually rises as the dormant state elapses. Reaches the maximum voltage VSUP output.

  Next, when the wireless unit 40 expires and operates after a predetermined suspension period, a current is supplied to the wireless unit 40 from the power supply voltage generation unit 20 and the power storage unit C1. At this time, if the consumption current of the wireless unit 40 is larger than the current output from the power supply voltage generation unit 20, current is also supplied from the power storage unit C1 to the wireless unit 40, and the voltage of the power storage unit C1 gradually increases with time. It goes down. Therefore, the voltage threshold Vthh and the capacity of the power storage unit C1 are determined in advance so that the voltage of the power storage unit C1 does not fall below the minimum voltage Vmin at which the radio unit 40 operates due to the operation of the wireless unit 40.

  In this embodiment, the voltage monitoring unit 21 continues to hold the ON command given to the power supply control unit 22 even if the voltage of the power storage unit C1 falls below the voltage threshold Vthh. Then, after the voltage at both ends of the power storage unit C1 is lower than the minimum operating voltage Vmin of the wireless unit 40 and the operation of the wireless unit 40 is stopped, the voltage at both ends of the power supply control unit 22 also decreases, and the on command cannot be held. The power control unit 22 is turned off.

  Thus, the current monitoring device according to the first embodiment of the present invention configured as described above is wireless until the voltage at both ends of the power storage unit C1 reaches the voltage threshold Vthh which is a voltage sufficient for the wireless unit 40 to operate. Since no current flows through the unit 40, even if the current flowing through the transmission line 2 is small, it is necessary for the radio unit 40 to operate as shown in the graph showing the voltage change across the power storage unit C1 in FIG. A minimum operating voltage Vmin (in the case of the wireless unit 40 described above, for example, 2.9 V) can be obtained.

  Next, the operation of the current monitoring device according to the second embodiment of the present invention will be described with reference to the graph shown in FIG. In this embodiment, in addition to the first embodiment described above, when the voltage of both ends of the power storage unit C1 is further lowered due to the operation of the wireless unit 40 and the wireless unit 40 is about to reach the minimum operating voltage Vmin, A voltage threshold Vthl slightly higher than the minimum operating voltage Vmin (second voltage threshold: a voltage lower than a voltage threshold Vthh (hereinafter referred to as the first voltage threshold) that is sufficient for the radio unit 40 to operate). The voltage monitoring unit 21 detects this, and outputs to the power supply control unit 22 an off command for interrupting the supply of current to the radio unit 40. Incidentally, the relationship between the voltage levels detected by the voltage monitoring unit 21 is [VSUP> Vthh> Vthl> Vmin].

  In the current monitoring device according to the second embodiment of the present invention, a current is output from the power supply voltage generation unit 20 when a current flows through the transmission line 2 as in the above-described embodiment. And the electrical storage part C1 is charged with the electric current output from the power supply voltage generation part 20, and the voltage of the both ends becomes high gradually with progress of time. Thereafter, when the voltage monitoring unit 21 detects that the first voltage threshold value Vthh sufficient for the wireless unit 40 to operate is detected, the voltage monitoring unit 21 outputs a control signal (ON command) to the power supply control unit 22, and the wireless unit 40 is supplied with current from the power supply voltage generation unit 20 and the power storage unit C1.

  Then, the wireless unit 40 starts an initial operation as described above, performs predetermined initialization, and shifts to a dormant state. The wireless unit 40 repeats the pause / operation of the wireless unit 40 at a predetermined cycle (for example, at intervals of 1 second). When the wireless unit 40 is in a dormant state, the power storage unit C1 is charged by the output current of the power supply voltage generating unit 20, and the voltage at both ends gradually increases with the elapse of the dormant state, and the power supply voltage generating unit 20 eventually outputs. Reaches the maximum voltage VSUP.

  Next, when the wireless unit 40 expires and operates after a predetermined suspension period, power is supplied to the wireless unit 40 from the power supply voltage generation unit 20 and the power storage unit C1. At this time, if the consumption current of the wireless unit 40 is larger than the current output from the power supply voltage generation unit 20, the charge stored in the power storage unit C1 is supplied to the wireless unit 40 as a current, and gradually increases with time. The voltage of C1 decreases.

When the voltage monitoring unit 21 detects that the voltage is lower than the first voltage threshold Vthh of the power storage unit C1 and further lower than the second voltage threshold Vthl, the voltage monitoring unit 21 supplies the radio unit 40 with the power supply control unit 22. Give off command to cut off current.
When the current supplied to the wireless unit 40 is cut off, the current output from the power supply voltage generation unit 20 charges the power storage unit C1. Therefore, the voltage across power storage unit C1 gradually increases with time. Then, when the voltage across the power storage unit C1 exceeds the first voltage threshold value Vthh, the voltage monitoring unit 21 gives an ON command to the power supply control unit 22 to operate the radio unit 40.

  Incidentally, when the power storage unit C1 is configured by a capacitor or the like, it is necessary that the electrostatic capacity does not fall below the second voltage threshold Vthl even during the initial operation and intermittent operation of the wireless unit 40. Therefore, if the charge consumed in the initial operation of the wireless unit 40 is Qinit, the time required for the initial operation of the wireless unit 40 is Tinit, and the minimum current value flowing through the transmission line 2 is Imin, the wireless unit 40 performs the initial operation. The capacitance C11 of the power storage unit C1 necessary for the calculation can be obtained by the following equation.

C11 = (Qinit−Imin · Tinit) / (Vthh−Vthl)
Similarly, if the charge consumed by the intermittent operation of the wireless unit 40 is Qint and the time required for the intermittent operation of the wireless unit 40 is Tint, the capacitance of the power storage unit C1 required for the wireless unit 40 to perform the intermittent operation. C12 can be obtained by the following equation.
C12 = (Qint−Imin · Tint) / (VSUP−Vthl)
The power storage unit C1 may select a capacitance that simultaneously satisfies each of the capacitances C11 and C12 thus determined. However, when the capacitance C of the power storage unit C1 is large, the time T1 until the voltage at both ends of the power storage unit C1 reaches the first threshold value Vthh increases as shown in the following equation.

T1 = C × Vthh / Imin
Therefore, it is desirable that the capacitance C of the power storage unit C1 is a capacitance that simultaneously satisfies the capacitances C11 and C12 obtained as described above and is as small as possible.
Thus, in the current monitoring device according to the second embodiment of the present invention configured as described above, the voltage at both ends of the power storage unit C1 is set to the first voltage threshold value Vthh that is sufficient for the radio unit 40 to operate. Until that time, not only does the current flow through the wireless unit 40, but also the voltage across the power storage unit C1 drops to reach the second voltage threshold Vthl before reaching the minimum operating voltage Vmin of the wireless unit 40. Since the current supplied to the wireless unit 40 is cut off and no current is supplied to the wireless unit 40 until the voltage across the power storage unit C1 exceeds the first voltage threshold value Vthh, the power storage unit C1 is reliably charged by the power supply voltage generation unit 20. The For this reason, since the voltage of the range which operates reliably is applied to the radio | wireless part 40, the radio | wireless part 40 can operate | move normally, without malfunctioning.

In the above-described embodiment, the current supplied to the radio unit 40 is controlled by the voltage monitoring unit 21 and the voltage control unit 22. However, instead of the radio unit 40 as shown in FIG. Needless to say, the circuit (1) 41 having a display for displaying the signal may be driven.
Next, a current monitoring device according to a third embodiment of the present invention will be described with reference to FIG. The third embodiment is different from the above-described embodiment in that a second circuit (circuit (2)) 42 is connected in parallel with the power supply voltage generation unit 20. The circuit (2) 42 is, for example, a CPU or an LCD display that operates with a small current less than 4 mA, which is the minimum current value flowing through the transmission line 2. That is, when the current flowing through the transmission line 2 is 4 mA, the minimum value of the current ISUP that can be passed from the power supply voltage generation unit 20 to the circuit after the power storage unit C1 is obtained by subtracting the current consumption of the circuit (2) 42 from 4 mA. Become a thing. In other words, in this embodiment, the circuit (2) 42 that consumes less current than the minimum current (for example, 4 mA) flowing through the transmission line 2 is operated in parallel with the power supply voltage generator 20 while the circuit (2 ) The power storage unit C1 is charged by the surplus current that has actuated 42.

However, since the circuit (2) 42 is connected in parallel with the power storage unit C1, it is necessary to wait for the voltage to rise until the voltage across the power storage unit C1 becomes a voltage necessary for the operation of the circuit (2) 42.
Thus, in the current monitoring device according to the third embodiment of the present invention, the circuit (2) 42 is operated by the current output from the power supply voltage generation unit 20 regardless of the control of the voltage monitoring unit 21 and the power supply control unit 22. In addition, the power storage unit C1 can be charged by the surplus current that operates the circuit (2) 42. The voltage across the circuit (2) 42 is equal to the voltage across the battery C1. When the minimum operating voltage of the circuit (2) 42 is lower than Vthh, the circuit (2) 42 is earlier than the circuit (1) 41 starts to operate in the first embodiment or the second embodiment. Can be activated. For this reason, even if it is a part of a circuit, a circuit can be operated at an early timing, and waiting time can be reduced.

Next, a current monitoring device according to a fourth embodiment of the present invention will be described with reference to FIG. This fourth embodiment is a modification of the above-described third embodiment, in which the constant current unit 50 is connected to the power supply line (VSUP line 12 in FIG. 8) between the circuit (2) and the power storage unit C1. It is in the point which provided. The constant current unit 50 plays a role of charging the power storage unit C1 with a constant current I ₀ (eg, 3 mA) smaller than the minimum current (eg, 4 mA) flowing through the transmission line 2. The surplus current I ₂ of the constant current I ₀ flowing through the constant current unit 50 is supplied to the circuit (2) 42 connected in parallel to the output of the power supply voltage generation unit 20.

  Thus, since the current monitoring device according to the fourth embodiment of the present invention is configured to charge the power storage unit C1 with a constant current by the constant current unit 50, the constant current unit 50 is viewed from the circuit (2) 42. Even if the circuit impedance is high and therefore the voltage at both ends of the power storage unit C1 is low, the voltage on the output side of the power supply voltage generation unit 20 can be kept high, and the current monitor device 10 is connected to the 4/20 mA transmission line 2 Thereafter, the circuit (2) 42 can be operated immediately.

  The current monitoring device of the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention.

The principal part schematic block diagram which shows the principal part of the current monitor apparatus which concerns on 1st embodiment of this invention. FIG. 2 is a circuit diagram illustrating a configuration example of a power supply control unit illustrated in FIG. 1. The figure which shows the relationship between the voltage of the both ends of the electrical storage part in the current monitor apparatus shown in FIG. 1, and the control signal which a voltage monitoring part outputs. The graph which shows the relationship between the electric current which flows through a transmission line, and the voltage of an electrical storage part both ends. The figure which shows the relationship between the voltage of the electrical storage part in the current monitoring apparatus which concerns on 2nd embodiment of this invention, and the control signal which a voltage monitoring part outputs. The principal part schematic block diagram which shows the principal part of the current monitor apparatus which concerns on another embodiment which deform | transformed 2nd embodiment of this invention. The principal part schematic block diagram which shows the principal part of the current monitor apparatus which concerns on 3rd embodiment of this invention. The principal part schematic block diagram which shows the principal part of the current monitor apparatus which concerns on 4th embodiment of this invention. The schematic block diagram which shows the fundamental structure of the industrial measurement system using the conventional 2-wire transmission line. The schematic block diagram which shows the fundamental structure of the industrial measurement system which provided the wireless monitoring apparatus in the industrial measurement system shown in FIG. The principal part schematic block diagram which shows the principal part of the current monitor apparatus which inventors devised. The graph which shows an example of the relationship between the voltage given to a radio | wireless part, and consumption current.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Industrial measuring instrument 2 Transmission line 3 DC power supply 4 Load resistor 5 Wireless monitoring apparatus 6 Battery 10 Current monitoring apparatus 11 GND line 12 VSUP line 20 Power supply voltage generation part 21 Voltage monitoring part 22 Power supply control part 30 Current detection part 40 Wireless Part

Claims (5)

A current monitoring device that measures a current value converted from a physical quantity measured by a measuring instrument into a signal current and output to two transmission lines,
A current detection unit that is inserted in the transmission path and measures the current value of the signal current;
A power supply voltage generation unit that outputs a voltage generated at both ends of the transmission line, when the signal current flows through the transmission line; and
A power storage unit that is connected in parallel to both ends of the power supply voltage generation unit and stores a current output from the power supply voltage generation unit;
A voltage monitoring unit connected to both ends of the power storage unit, monitoring a voltage at both ends, and outputting a control signal when detecting that the voltage exceeds a predetermined voltage value;
A current control unit configured to connect the power supply voltage generation unit and the power storage unit to a predetermined first circuit and operate the circuit when the control signal is output from the voltage monitoring unit; Monitor device.   The current monitoring apparatus according to claim 1, wherein the voltage monitoring unit holds the output of the control signal when detecting that the voltage across the power storage unit exceeds a predetermined voltage value.   The voltage monitoring unit holds the output of the control signal when it detects that the voltage at both ends of the power storage unit exceeds a predetermined first voltage value, and the voltage at both ends of the power storage unit is 2. The current monitor device according to claim 1, wherein the output of the control signal is stopped when it is detected that the voltage value is lower than a second voltage value lower than the first voltage value. The current monitoring device according to any one of claims 1 to 3,
Furthermore, a second circuit that is connected and operated in parallel at both ends of the power supply voltage generation unit, and a constant current that is inserted between the power supply voltage generation unit and the power storage unit to flow a predetermined current into the power storage unit A current monitoring device.   The current monitor device according to claim 1, wherein the first circuit is a wireless unit that wirelessly transmits a current value measured by the current detection unit.

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