Field Devices

Abstract

To automatically correct the resonance frequency of wireless communication used in a field apparatus.SOLUTION: A resonance circuit 11 is provided with a variable capacitance circuit 11C connected to a fixed capacitance circuit 11B, and includes a capacitance adjustment circuit 16 that adjusts a capacitance component of the variable capacitance circuit 11C so that an overall capacitance component of the entire resonance circuit 11 becomes equal to a preset reference capacitance component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an antenna resonance frequency correction technique for correcting the resonance frequency of short-range wireless communication used in a field device. [Background technology]

[0002] Various field devices used for remote control of equipment are installed in large-scale facilities such as factories, plants, and buildings. Some of these field devices have a near field communication (NFC) function for data communication with external devices (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-107060 A Summary of the Invention [Problem to be solved by the invention]

[0004] NFC communicates at a specific resonance frequency, but the capacitance component that determines this resonance frequency increases or decreases depending on the presence or absence of metal materials near the antenna coil. For example, a capacitance component occurs between the wiring patterns formed on the substrate to connect the NFC IC chip and the antenna coil, via the substrate, and this capacitance component is considered to be almost constant.

[0005] On the other hand, a capacitance component occurs between the wiring that forms the antenna coil via the metal that is present near the antenna coil, but the capacitance component changes depending on the positional relationship between the metal and the antenna coil. Therefore, after long-term use or poor assembly precision, the resonant frequency changes when the cover is opened and closed during maintenance, which causes a problem of reduced communication distance.

[0006] The present invention has been made to solve such problems, and has an object to provide an antenna resonant frequency correction technique that can automatically correct the resonant frequency of wireless communication used in a field device. [Means for solving the problem]

[0007] In order to achieve this objective, the field device of the present invention comprises a resonant circuit having an antenna coil and a fixed capacitance circuit, a wireless communication circuit that uses the resonant circuit to wirelessly communicate with an external device, and a capacitance adjustment circuit that adjusts the capacitance component of the resonant circuit, the resonant circuit having a variable capacitance circuit connected to the fixed capacitance circuit, and the capacitance adjustment circuit is configured to adjust the capacitance component of the variable capacitance circuit so that the overall capacitance component of the entire resonant circuit is equal to a predetermined reference capacitance component.

[0008] In addition, in one configuration example of the field device according to the present invention, the fixed capacitance circuit is connected between a first node through which a wireless communication signal flows and a second node connected to a fixed potential, and the variable capacitance circuit is connected in parallel with the fixed capacitance circuit.

[0009] In one configuration example of the field device according to the present invention, one end of the antenna coil is connected to the first node directly or via a resistive element, and the other end is connected to the second node.

[0010] Furthermore, one configuration example of the above-mentioned field device according to the present invention further includes a capacitance detection circuit that detects the entire capacitance component from the resonant circuit, and the capacitance adjustment circuit is configured to adjust the capacitance component of the variable capacitance circuit so that the capacitance component of the entire resonant circuit detected by the capacitance detection circuit becomes equal to a preset reference capacitance component.

[0011] In addition, one configuration example of the field device according to the present invention is configured such that the capacitance detection circuit samples the voltage of the first node at a constant period and supplies the obtained detection voltage to the capacitance adjustment circuit, and the capacitance adjustment circuit adjusts the capacitance component of the variable capacitance circuit so that the obtained detection voltage becomes equal to a reference voltage corresponding to the reference capacitance component.

[0012] In addition, in one configuration example of the field device according to the present invention, the capacitance detection circuit has a voltage holding capacitive element for holding the detection voltage, a first switch having one end connected to an initialization potential, a second switch having one end connected to the first node and the other end connected to the first switch, and a third switch having one end connected to the other end of the second switch and the other end connected to the voltage holding capacitive element, and is configured to charge the fixed capacitance circuit and the variable capacitance circuit with the initialization potential by turning on the first switch and the second switch and turning off the third switch, to supply the charged charges of the fixed capacitance circuit and the variable capacitance circuit to the voltage holding capacitive element by turning off the first switch and turning on the second and third switches, and to supply the detection voltage to the capacitance adjustment circuit by turning off the first switch, the second switch, and the third switch. Effect of the Invention

[0013] According to the present invention, it is possible to automatically correct the resonance frequency of wireless communication used in a field device. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram showing a configuration of a field device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram showing a configuration of a field device according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a circuit diagram showing details of the resonant circuit and the capacitive sensing circuit. [Figure 4]FIG. 4 is an explanatory diagram showing the capacitance detection operation. [Diagram 5] FIG. 5 is a block diagram showing a configuration of a field device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, an embodiment of the present invention will be described with reference to the drawings. [Embodiments of the present invention] First, a field device 10 according to an embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a block diagram showing a configuration of a field device according to an embodiment of the present invention. Fig. 2 is an explanatory diagram showing a configuration of a field device according to an embodiment of the present invention.

[0016] This field device 10 is a terminal device that is installed in large facilities such as factories, plants, and buildings, and is used for remote control of the equipment, and is configured to communicate data with external devices via wireless communication such as short-range wireless communication.

[0017] As shown in FIG. 1, the field device 10 includes, as main circuit sections, an antenna coil 11A, a fixed capacitance circuit 11B, a variable capacitance circuit 11C, a wireless communication circuit 12, a control circuit 13, a display 14, a capacitance detection circuit 15, and a capacitance adjustment circuit 16.

[0018] Of these, the antenna coil 11A, the fixed capacitance circuit 11B, and the variable capacitance circuit 11C form a resonant circuit 11. Moreover, the fixed capacitance circuit 11B, the variable capacitance circuit 11C, the wireless communication circuit 12, the control circuit 13, the capacitance detection circuit 15, and the capacitance adjustment circuit 16, excluding the antenna coil 11A and the display 14, are mounted on one or more board units 10A.

[0019] As shown in FIG. 2, the board unit 10A, the antenna coil 11A, and the display 14 are fixed in the internal space of the metal housing 1 by using, for example, a display frame 2, and are sealed from the outside by a cover 3.

[0020] [Field devices] Next, each circuit unit of the field device 10 will be described in detail with reference to FIG.

[0021] [Resonant circuit] The resonant circuit 11 is configured such that the antenna coil 11A, the fixed capacitance circuit 11B, and the variable capacitance circuit 11C are connected in parallel to each other and resonate (tune) with a radio frequency used in wireless communication. In this embodiment, the capacitance of the resonant circuit including the fixed capacitance circuit 11B and the variable capacitance circuit 11C is referred to as the total capacitance component.

[0022] [Wireless communication circuit] The wireless communication circuit 12 is configured to perform wireless communication with an external device EX such as an NFC reader / writer via the resonant circuit 11.

[0023] [Control circuit] The control circuit 13 has a CPU and its peripheral circuits, and is configured to control the operation of the entire field device 10 and to perform data communication with the external device EX via the wireless communication circuit 12. [Display] The display unit 14 is a display device such as an LCD, and is configured to visually display the data output from the control circuit 13 .

[0024] [Capacitive sensing circuit] The capacitance detection circuit 15 is configured to detect the total capacitance component from the resonant circuit 11 to the entire resonant circuit. [Capacity adjustment circuit] The capacitance adjustment circuit 16 is configured to adjust the capacitance component of the variable capacitance circuit 11C so that the total capacitance component of the resonant circuit 11 detected via the capacitance detection circuit 15 becomes equal to a preset reference capacitance component.

[0025] [Operation of the embodiment of the present invention] Next, the capacitance adjustment operation of the field device 10 according to the present embodiment will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a circuit diagram showing the details of the resonant circuit and the capacitance detection circuit. Fig. 4 is an explanatory diagram showing the capacitance detection operation.

[0026] 3, in the resonant circuit 11, the fixed capacitance circuit 11B is connected between a first node N1 through which a wireless communication signal flows and a second node N2 connected to a ground potential (fixed potential) GND, and the variable capacitance circuit 11C is connected in parallel to the fixed capacitance circuit 11B. One end of the antenna coil 11A is connected to N1 via a resistive element Rr, and the other end is connected to N2. In this case, one end of the antenna coil 11A may be directly connected to N1.

[0027] The resonant circuit 11 is provided with a parallel connection circuit CR of a capacitance element Cx and a resistance element Rx, with one end of CR connected to N1 via a switch SW4 and the other end of CR connected to GND. The resonant circuit 11 and the wireless communication circuit 12 are connected via two diodes D1 and D2. In this case, the anode terminal of D1 is connected to one end of CR, and the cathode terminal is connected to the wireless communication circuit 12. The cathode terminal of D2 is connected to GND, and the anode terminal is connected to the wireless communication circuit 12.

[0028] The capacitance detection circuit 15 has three switches SW1 (first switch), SW2 (second switch), and SW3 (third switch) and a voltage holding capacitance element Cs. One end of SW1 is connected to an initialization potential Va, and the other end is connected to the other end of SW2. One end of SW2 is connected to a first node N1 of the resonance circuit 11. One end of SW3 is connected to the other end of SW2, and the other end is connected to one end of the voltage holding capacitance element Cs. The voltage holding capacitance element Cs is a capacitance element for holding a voltage detected by the capacitance detection circuit 15.

[0029] By switching operations of SW1, SW2, and SW3, the capacitance detection circuit 15 samples the detection voltage Vs, which is the potential of N1 of the resonant circuit 11, charges Cs, and outputs it to the capacitance adjustment circuit 16. The capacitance adjustment circuit 16 adjusts the capacitance component of the variable capacitance circuit 11C so that Vs detected by the capacitance detection circuit 15 becomes equal to a reference voltage Vr corresponding to the reference capacitance component of the resonant circuit 11.

[0030] 4, in the initialized state, SW1, SW2, and SW3 are turned off, and SW4 is turned on, so that the resonant circuit 11 and the wireless communication circuit 12 are connected to each other.

[0031] In a start state (start) when sampling starts, SW3 and SW4 are turned off, and SW1 and SW2 are turned on. As a result, an initialization potential Va is supplied to the fixed capacitance circuit 11B and the variable capacitance circuit 11C via SW1 and SW2, and the fixed capacitance circuit 11B and the variable capacitance circuit 11C are charged by Va.

[0032] Next, in a sampling state, SW1 and SW4 are turned off and SW2 and SW3 are turned on, so that the charges stored in the fixed capacitance circuit 11B and the variable capacitance circuit 11C are supplied to the voltage holding capacitance element Cs via SW2 and SW3.

[0033] After that, in a finish state (finish) where sampling ends, SW1, SW2, and SW3 are turned off and SW4 is turned on, similar to the initialization state (initial). As a result, the resonant circuit 11 and the wireless communication circuit 12 are connected, the voltage holding capacitive element Cs is disconnected from N1 and Va, and the voltage Vs held in the voltage holding capacitive element Cs is supplied to the capacitance adjustment circuit 16. The capacitance adjustment circuit 16 uses the supplied voltage Vs to adjust the capacitance component of the variable capacitance circuit 11C.

[0034] The period of the series of sampling processes from the initialization state to the finish state can be determined appropriately according to the environment in which the field device is installed, etc. For example, the sampling process may be performed at a predetermined fixed period.

[0035] If the total capacitance component of the entire resonant circuit is Ca and the charged charge is Q, then in the charged state, the relationship of the following equation (1) holds. Q = Ca × Va … (1)

[0036] On the other hand, in the sampling state, the total capacitance component Ca and the voltage holding capacitance element Cs are connected in parallel, so that the reference voltage Vr of Vs is expressed by the following equation (2). Vr = Q / (Ca + Cs) … (2)

[0037] Therefore, by substituting equation (1) into equation (2), we obtain the following equation (3). Vr = Va{Ca / (Ca+Cs)} …(3)

[0038] Here, the capacitances of the fixed capacitance circuit 11B and the variable capacitance circuit 11C are C1 and C2, respectively. When the total capacitance component Ca does not change, that is, when Ca=C1+C2 (reference capacitance component), Vs output from the capacitance detection circuit 15 is equal to Vr calculated by equation (3). On the other hand, when Ca changes, that is, when Ca≠C1+C2, an error occurs between Vs and Vr according to the change in Ca.

[0039] Therefore, the capacitance C2 of the variable capacitance circuit 11C is adjusted based on this error so that Vs becomes Vr, i.e., Ca=C1+C2. As a specific adjustment method, various well-known adjustment methods can be used. For example, a method of repeatedly fine-tuning the value of the capacitance C2 by a certain adjustment width until Vs becomes approximately equal to Vr is conceivable. Also, it is not necessary to adjust Vs to exactly match Vr, but it is sufficient that Vs falls within a predetermined error range with respect to Vr.

[0040] [Advantages of the embodiment of the present invention] In this manner, in this embodiment, the resonant circuit 11 is provided with a variable capacitance circuit 11C connected to a fixed capacitance circuit 11B, and the capacitance adjustment circuit 16 is configured to adjust the capacitance component of the variable capacitance circuit 11C so that the overall capacitance component of the resonant circuit 11 becomes equal to a preset reference capacitance component.

[0041] More specifically, it is provided with a capacitance detection circuit 15 that detects the entire capacitance component of the resonant circuit 11, and a capacitance adjustment circuit 16 is configured to adjust the capacitance component of the variable capacitance circuit 11C so that the capacitance component of the entire resonant circuit detected by the capacitance detection circuit 15 becomes equal to a preset reference capacitance component.

[0042] This allows automatic correction of the total capacitance component of the resonant circuit 11 used in the field device 10, and as a result, automatic correction of the resonant frequency used in wireless communication is possible. Therefore, even if the total capacitance component changes due to the positional relationship between the antenna coil 11A and metal present near the antenna coil 11A, the resonant frequency is automatically corrected by adjusting the variable capacitance component and maintained. This makes it possible to avoid deterioration of wireless communication performance, such as a reduction in communication distance, caused by a change in the total capacitance component.

[0043] [Other embodiments] Next, a field device 10 according to another embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 is a block diagram showing the configuration of a field device according to another embodiment. In this embodiment, a case will be described in which the capacitance adjustment circuit 16 described in Fig. 1 is realized by a control circuit 13.

[0044] That is, the control circuit 13 is configured to adjust the capacitance component of the variable capacitance circuit 11C so that the total capacitance component of the resonant circuit 11 detected via the capacitance detection circuit 15 becomes equal to a preset reference capacitance component.

[0045] This allows the configuration of the capacitance adjustment circuit 16 to be realized by the CPU of the control circuit 13, thereby reducing the circuit size and circuit costs. In particular, if a CPU having an A / D conversion port is used as the CPU used in the control circuit 13, the A / D conversion circuit used in the capacitance adjustment circuit 16 can be omitted, and the circuit size and circuit costs can be further reduced.

[0046] [Extended embodiment] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, the respective embodiments can be implemented in any combination within a range that does not contradict each other. [Explanation of symbols]

[0047] 1...metal housing, 2...display frame, 3...cover, 10...field device, 11...resonant circuit, 11A...antenna coil, 11B...fixed capacitance circuit, 11C...variable capacitance circuit, 12...wireless communication circuit, 13...control circuit, 14...display, 15...capacitance detection circuit, 16...capacitance adjustment circuit.

Claims

1. a resonant circuit having an antenna coil and a fixed capacitance circuit; a wireless communication circuit that wirelessly communicates with an external device using the resonant circuit; a capacitance adjustment circuit for adjusting a capacitance component of the resonant circuit, the resonant circuit includes a variable capacitance circuit connected to the fixed capacitance circuit, the capacitance adjustment circuit is configured to adjust a capacitance component of the variable capacitance circuit so that an overall capacitance component of the entire resonant circuit becomes equal to a preset reference capacitance component; the fixed capacitance circuit is connected between a first node through which a wireless communication signal flows and a second node connected to a fixed potential; the variable capacitance circuit is connected in parallel with the fixed capacitance circuit, a capacitance detection circuit for detecting the total capacitance component from the resonant circuit; The capacitance adjustment circuit is configured to adjust the capacitance component of the variable capacitance circuit so that the capacitance component of the entire resonant circuit detected by the capacitance detection circuit becomes equal to a preset reference capacitance component.

1. A field device comprising:

2. 2. The field device according to claim 1, The field device is characterized in that one end of the antenna coil is connected to the first node via a resistive element or directly, and the other end is connected to the second node.

3. 2. The field device according to claim 1, the capacitance detection circuit samples the voltage of the first node at a constant period and supplies the obtained detection voltage to the capacitance adjustment circuit; The capacitance adjustment circuit adjusts the capacitance component of the variable capacitance circuit so that the obtained detection voltage is equal to a reference voltage corresponding to the reference capacitance component.

1. A field device comprising:

4. 4. The field device according to claim 3, The capacitance detection circuit includes: a voltage holding capacitive element for holding the detection voltage; A first switch having one end connected to an initialization potential; a second switch having one end connected to the first node and the other end connected to the first switch; a third switch having one end connected to the other end of the second switch and the other end connected to the voltage holding capacitive element; by turning on the first switch and the second switch and turning off the third switch, the fixed capacitance circuit and the variable capacitance circuit are charged with the initialization potential; supplying the charges of the fixed capacitance circuit and the variable capacitance circuit to the voltage holding capacitance element by turning off the first switch and turning on the second and third switches; The detection voltage is supplied to the capacitance adjustment circuit by turning off the first switch, the second switch, and the third switch.

1. A field device comprising:

Images