WO2010110113A1

WO2010110113A1 - Field device

Info

Publication number: WO2010110113A1
Application number: PCT/JP2010/054358
Authority: WO
Inventors: 立鄭
Original assignee: 株式会社山武
Priority date: 2009-03-24
Filing date: 2010-03-15
Publication date: 2010-09-30
Also published as: JP2010226878A; JP5358236B2

Abstract

Provided is a field device capable of carrying out communication with high power efficiency. The field device comprises a wireless circuit (14) for carrying out wireless communication, an analog signal input unit (13) to which an analog signal is inputted, at least one capacitor (21) provided to supply power to the wireless circuit (14), a power supply circuit (15) provided to charge the capacitor (21) on the basis of the analog signal, a measuring circuit (16) connected in series to the power supply circuit (15), a switch unit (23) for switching between a first (charge) state and a second (discharge) state, and a switch control circuit (20) for controlling the switch unit (23) to intermittently carry out the switching. In the first (charge) state, the capacitor (21) is connected in parallel to the power supply circuit (15), and in the second (discharge) state, the capacitor (21) is connected in parallel to the wireless circuit (14).

Description

Field equipment

The present invention relates to a field device, and more particularly to a field device having a wireless communication function.

Various field devices are installed in facilities such as plants and factories. The field device detects physical quantities such as temperature, flow rate, pressure, and position. Then, by collecting field data from such field devices, it is possible to control and manage facilities.

Among such field devices, one having a wireless communication function is disclosed (see Patent Document 1). In this document, a valve positioner, which is a field device, receives a 4-20 mA current signal. Based on this current signal, an operation signal is output so that the valve is at a predetermined valve position. By performing wireless communication, wiring costs can be reduced. For example, the field device further supplies the surplus current from the 4-20 mA signal (loop current) to the storage battery or the capacitor in the field device of Patent Document 1. (Claim 6)

JP 2006-157865 A

In the field device of Patent Document 1, a loop current is shunted to supply power to the radio circuit. That is, a loop current of 4-20 mA is shunted between the measurement circuit and the power supply circuit of the radio circuit. Here, since the electric power by the loop current is mostly used in the existing measurement circuit, the capacitor cannot be sufficiently charged. For example, of the 4-20 mA loop current, the maximum current that can be used to charge the capacitor is about 0.5 mA.

The present invention has been made to solve such problems, and an object of the present invention is to provide a field device capable of wirelessly communicating with power efficiently.

A field device according to a first aspect of the present invention includes a wireless circuit that performs wireless communication, an analog signal input unit that receives an analog signal, and a single capacitor that is provided to supply power to the wireless circuit. A power circuit provided to charge the capacitor based on the analog signal; a measurement circuit connected in series to the power circuit; and a first capacitor connected in parallel to the power circuit. A switch unit that switches between a state and a second state connected in parallel to the wireless circuit, and a switch control unit that controls the switching by the switch unit to be performed intermittently. As a result, wireless communication can be performed efficiently.

A field device according to a second aspect of the present invention is the above-described field device, for supplying a power to the wireless circuit that performs wireless communication, an analog signal input unit that receives an analog signal, and the wireless circuit. A plurality of capacitors, a power supply circuit provided for charging the capacitor based on the analog signal, a measurement circuit connected in series to the power supply circuit, and the plurality of capacitors, A switch unit for switching between a first state connected in parallel to the power supply circuit and a second state where the plurality of capacitors are connected in parallel and connected in parallel to the wireless circuit, and switching by the switch unit And a switch control unit that performs control so as to be performed intermittently. As a result, wireless communication can be performed efficiently.

A field device according to a third aspect of the present invention is the above-described field device, and in the second state, the positive pole of the capacitor is connected to the positive terminal side of the wireless circuit, and the negative pole of the capacitor is The wireless circuit and the measurement circuit are grounded to a common ground. Thereby, wireless communication with strong noise tolerance can be performed.

A field device according to a fourth aspect of the present invention is the field device described above, wherein the capacitance value of the capacitor is obtained from an operating characteristic of the radio circuit and an operating cycle of the switch unit. Is. Thereby, sufficient electric power for wireless communication can be supplied simply.

A field device according to a fifth aspect of the present invention is the field device described above, wherein the switch is configured by a semiconductor switch, and a switch control signal line is insulated from the switch. .

According to the present invention, it is possible to provide a field device that can perform wireless communication efficiently without damaging the original measurement function.

It is a circuit diagram which shows the structure of the field apparatus concerning this Embodiment. It is a figure which shows the state in which the field apparatus concerning this Embodiment is charged. It is a figure which shows the state by which the field apparatus concerning this Embodiment is discharged. It is a timing chart which shows the operation timing of the field device concerning this embodiment. It is a figure which shows the structure of the switch control circuit provided in the field device concerning this Embodiment. It is a figure which shows the state in which the field apparatus of another structure is charged. It is a figure which shows the state in which the field apparatus of another structure is discharged.

The field device according to this embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram showing a configuration of a field device. Field devices are installed in plants, factories, and other facilities. Examples of field devices include transmitters and valve positioners. Of course, various sensors that detect physical quantities such as temperature, flow rate, pressure, and position may be used.

The field device 10 includes an analog signal input unit 13, a radio circuit 14, a power supply circuit 15, and a measurement circuit 16. The analog signal input unit 13 receives an analog signal. The analog signal is, for example, a loop current of 4 to 20 mA. Therefore, the analog signal input unit 13 has a terminal 11 and a terminal 12. Then, a loop current of 4 to 20 mA flows from the terminal 11 to the terminal 12. This loop current changes according to the value of the measurement data. For example, data values such as pressure are converted into loop currents. Further, for example, a power supply voltage of 24 V is applied to the analog signal input unit 13.

The wireless circuit 14 has a wireless communication function for performing wireless communication with the outside. The radio circuit 14 includes, for example, an antenna, a modulator, and a demodulator. The wireless circuit 14 wirelessly transmits various signals such as collected measurement data. This wireless signal is received by an external information processing apparatus, and field data is collected. Alternatively, parameter data to be set is transmitted from the outside wirelessly. This eliminates the need for external wiring or the like. It becomes possible to easily install and maintain field devices in the facility.

The power supply circuit 15 is a circuit that generates power to supply power to the wireless circuit 14. Therefore, a loop current is input to the power supply circuit 15. Then, a predetermined power is supplied to the radio circuit 14 based on the loop current. The measurement circuit 16 also has a built-in circuit (such as a regulator) that supplies its own power from a loop current.

The measurement circuit 16 measures data. The measurement circuit 16 is connected in series to the power supply circuit 15. That is, the power supply circuit 15 and the measurement circuit 16 are connected in series between the terminal 11 and the terminal 12. The radio circuit 14 and the measurement circuit 16 are connected to a common ground 19. The ground 19 is connected to a case (housing) of the field device 10, for example. Thereby, it can be operated stably.

Furthermore, the power supply circuit 15 is provided with a switch unit 23 that is one of the technical features of the field device 10 according to the present embodiment. The switch unit 23 is provided with a capacitor 21 and a switch 22. Here, four capacitors 21 are provided. In order to switch the connection of the four capacitors 21, eight switches 22 are provided. That is, the switches 22 are connected to both sides of each capacitor 21. And the connection state of the capacitor 21 changes when all the switches 22 are switched at the same timing. The switch 22 is configured by a semiconductor switch such as a semiconductor transistor, for example.

Between the switch unit 23 and the wireless circuit 14, a diode 17 for preventing backflow is provided. Further, a constant current diode 18 for preventing backflow is provided between the measurement circuit 16 and the radio circuit 14. The wireless circuit 14 is provided with a switch control circuit 20. The switch control circuit 20 is implemented by a microcomputer, for example, and outputs a control signal for controlling switching of the switch unit 23. Further, the switch control circuit 20 can acquire various measurement data of the measurement circuit 16. The switch control circuit 20 may not be built in the wireless circuit 14. That is, the switch control circuit 20 may be provided at a place other than the wireless circuit 14. For example, the switch control circuit 20 may be provided in the measurement circuit 16 or may be provided in other places.

The switch unit 23 switches the connection state of the four capacitors 21. While the wireless circuit 14 performs wireless communication, the switch unit 23 places the capacitor 21 in a discharged state. As a result, the radio circuit 14 is driven by the electric power stored in the capacitor 21. On the other hand, when the wireless circuit 14 does not perform wireless communication, the switch unit 23 places the capacitor 21 in a charged state. As a result, the power used during wireless communication is stored in the capacitor 21. Switching of the connection state of the switch unit 23 is executed by the switch control circuit 20. The switch control circuit 20 switches the connection state intermittently. For example, the switch control circuit 20 outputs a pulse signal that switches the switch 22 at a predetermined cycle. Thereby, all the switches 22 are switched simultaneously. Therefore, the discharge state and the charge state are switched intermittently.

Here, the charged state of the capacitor 21 will be described with reference to FIG. FIG. 2 is a circuit diagram showing a state of charge, and a part of the configuration is omitted as appropriate. As shown in FIG. 2, in the charged state, four capacitors 21 are connected in parallel. The four capacitors 21 are connected to the power supply circuit 15 and charged. In the charged state, the radio circuit 14 is disconnected from the capacitor 21. At this time, the radio circuit 14 is in a sleep state.

Next, the discharge state of the capacitor 21 will be described with reference to FIG. FIG. 3 is a circuit diagram showing a discharge state, and some components are omitted as appropriate. As shown in FIG. 3, in the discharged state, the four capacitors 21 are connected in series. These four capacitors 21 are connected to the radio circuit 14 in parallel and discharged. The plus end (positive electrode) of the capacitor 21 connected in series is connected to the + terminal side of the radio circuit 14, and the minus end (negative electrode) is connected to the ground. The electric charge accumulated in the capacitor 21 flows to the wireless circuit 14 through the diode 17, and power for wireless communication is supplied. The wireless circuit 14 performs wireless communication. In the discharged state, the power supply circuit 15 is disconnected from the capacitor 21.

Thus, the capacitor 21 is charged from the power supply circuit 15 at the time of sleep of the wireless operation. During charging, the power supply circuit 15 and the measurement circuit 16 are connected in series, and a plurality of capacitors 21 are connected in parallel to the power supply circuit 15. On the other hand, the sleep state of the wireless circuit can be maintained with a current of several μA from the power source of the measurement circuit 16. During the wireless communication operation, a plurality of charged capacitors 21 are connected in series by the switch 22. Further, the positive end and the negative end are connected to the power supply and ground of the wireless circuit to supply power. When the wireless communication operation is completed, the switch 22 is returned to the original state and the capacitor 21 is restored in parallel. Thereby, the capacitor 21 is charged. By doing in this way, wireless power can be supplied efficiently. Therefore, wireless communication can be performed without using an AC power source or a battery. Therefore, installation in equipment can be easily performed. Wiring costs and battery maintenance costs can be reduced.

The switching operation between the charged state and the discharged state will be described with reference to FIG. FIG. 4 is a timing chart showing the switching operation.

As shown in FIG. 4, the switch control signal is a pulse signal having a predetermined cycle, and the switch 22 repeats ON / OFF. That is, the discharge period and the charge period are repeated at regular intervals. In the charging period, the sleep current of the wireless circuit 14 becomes the wireless consumption current. The capacitor 21 is charged while the wireless communication function is stopped. In this state, the measurement circuit 16 is connected in series with the power supply circuit. Therefore, the loop current is supplied to the measurement circuit 16. For this reason, the current loss of the measurement circuit 16 can be reduced. For example, even if the loop current is the lower limit of 4 mA, the current value supplied to the measurement circuit 16 does not fall below 4 mA. Since the capacitor 21 is connected to the power supply circuit 15 in parallel, some voltage drops in the power supply circuit 15. However, since current loss can be reduced, the measurement circuit 16 operates without problems even when the voltage drops.

On the other hand, in the discharge period, first, it flows with the microcomputer operating current, and the switch control circuit which is the microcomputer operates. A wireless operating current flows, and wireless communication is performed in the wireless circuit 14. The wireless operating current is about 10 mA, for example. Then, after the wireless communication is finished, the microcomputer operation is finished. By repeating this, wireless communication is intermittently performed. Wireless communication can be performed simply by outputting a switch control signal for intermittently performing wireless operation. That is, it is not necessary to monitor the state of charge, and it can be easily controlled.

Next, a specific example of the switch unit 23 will be described with reference to FIG. FIG. 5 is a diagram illustrating a specific example of the switch unit 23.

An isolator 51 is connected to the switch unit 23. That is, since the switch control circuit 20 and the power supply circuit 15 have different grounds, the isolator 51 is used. Then, a microcomputer control signal for controlling switch switching is input from the switch control circuit 20 to the isolator 51. The switch control signal line can be insulated from the switch by the isolator 51. The power V + of the switch unit 23 is supplied from a power circuit. The switch 22 is switched by the microcomputer control signal. The analog voltage range in which the switch 22 can be controlled is -0.5V to + 0.5V. Here, the switch 22 is driven by the electric power of the capacitor 21. That is, the switch 22 is operated by the electric power stored in the capacitor 21. For this reason, the ground GND of the switch unit 23 is connected to COM2 of the capacitor 21, and the power source V + is connected to COM1 of the capacitor 21.

In the above description, the number of capacitors 21 is four, but may be other than four. The number of capacitors 21 is preferably plural. Thereby, the voltage can be boosted. Moreover, as shown in FIGS. 6 and 7, the number of capacitors 21 may be one.

The power regulator voltage of the power circuit 15 may be about 0.5 to 1V. The power supply circuit 15 may be configured with a diode, a shunt regulator, a transistor, or the like.

Note that the characteristics of the capacitor 21 and the number of stages can be obtained from the operating characteristics and operating cycle of the radio circuit. The capacitance C of the capacitor 21 is approximated below. Here, for the sake of calculation, it is assumed that the intermittent operation has a cycle of 1 second and the wireless communication operation has a duty of 1% (that is, 0.01 seconds). The voltage regulator voltage of the power supply circuit 15 is V = 1.

The charge to be charged is obtained by Q = C × V = C (unit q: coulomb) (however, the charge time is negligible and is ignored). Here, if the wireless communication circuit consumes 10 mA, it is necessary to charge 0.1 mq or more for one wireless operation.

That is, in the case where there is one capacitor 21, 0.1 mq is required to flow 10 mA for 0.01 second. For that purpose, C = 0.1 mF (100 μF) or more is sufficient. However, this is a case where the wireless circuit 14 can operate at 1V.

Next, when the number of capacitors 21 is n, the series capacitor voltage is boosted to n × V, but if the necessity of flowing 10 mA for 0.1 second does not change, the charge to charge each capacitor is still 0.1 mq is required. In this case, the capacitance of the capacitor 21 needs to be C = 0.1 mF (100 μF) or more.
Of course, when the radio circuit 14 operates at an n × V voltage and consumes a current of 1 / n, the capacitor 21 needs only a small divided capacity of about 1 / n.
As described above, the number of stages and the characteristics (capacitance) of the capacitor 21 can be obtained from the operating characteristics and period of wireless communication. That is, the capacitance of the capacitor can be determined by the operation characteristics (current) of wireless communication and the operation cycle (duty, repetition frequency).

DESCRIPTION OF SYMBOLS 10 Field apparatus 11 Terminal 12 Terminal 14 Wireless circuit 15 Power supply circuit 16 Measuring circuit 17 Diode 18 Diode 19 Ground 20 Switch control part 21 Capacitor 22 Switch 23 Switch part 51 Isolator

Claims

A wireless circuit for performing wireless communication;
An analog signal input section to which an analog signal is input;
One capacitor provided to supply power to the radio circuit;
A power supply circuit provided for charging the capacitor based on the analog signal;
A measurement circuit connected in series to the power supply circuit;
A switch unit that switches between a first state in which the capacitor is connected in parallel to the power supply circuit and a second state in which the capacitor is connected in parallel to the wireless circuit;
And a switch control unit that controls the switching by the switch unit to be performed intermittently.
A wireless circuit for performing wireless communication;
An analog signal input section to which an analog signal is input;
A plurality of capacitors provided to supply power to the radio circuit;
A power supply circuit provided for charging the capacitor based on the analog signal;
A measurement circuit connected in series to the power supply circuit;
A switch unit that switches between a first state in which the plurality of capacitors are connected in parallel to the power supply circuit and a second state in which the plurality of capacitors are connected in series and connected in parallel to the wireless circuit;
And a switch control unit that controls the switching by the switch unit to be performed intermittently.
In the second state, a positive pole of the capacitor is connected to a positive terminal side of the wireless circuit, and a negative pole of the capacitor is grounded to a common ground of the wireless circuit and the measurement circuit. The field device according to claim 1 or 2.
3. The field device according to claim 1, wherein the capacitance value of the capacitor is obtained from an operation characteristic of the wireless circuit and an operation cycle of the switch unit.
The switch comprises a semiconductor switch;
3. The field device according to claim 1, wherein a switch control signal line is insulated from the switch.