JP5629248B2 - Digital isolators and field devices - Google Patents

Description

  The present invention relates to a digital isolator that ensures electrical insulation of input / output signals between a primary circuit and a secondary circuit, and a field device using the digital isolator.

  Conventionally, field devices such as an electropneumatic positioner equipped with a CPU and ROM as a device that operates by receiving a signal (control signal current) in a predetermined current range sent from a host control device via a pair of electric wires. Is used.

  The field device operates by receiving a control signal current that changes in a current range of 4 to 20 mA, and includes an operation power supply circuit that generates its own operation power supply from the control signal current. The operation power supply generated by the operation power supply circuit Is sent to its own internal circuit. In this case, since it must operate even at a minimum of 4 mA, the operating current required for its own internal circuit is suppressed to 4 mA or less by a constant current circuit.

  On the other hand, in addition to the original function of control valve opening control, the electropneumatic positioner performs control valve abnormality diagnosis and self-diagnosis diagnosis, and the diagnosis results and actual valve opening are displayed on a personal computer, etc. There is also a demand for a function for outputting to external devices via communication.

  In such a two-wire field device that communicates with an external device, an isolator is interposed between a control unit configured with a CPU or the like inside the device and a communication circuit that communicates with the external device. To ensure electrical insulation between input and output signals.

  As this isolator, a digital isolator using a system such as a pulse transformer or an electrostatic capacity is often used as a communication system of an insulating part, in contrast to a photocoupler that has been widely used as an insulating circuit. . A digital isolator is a device having advantages such as a reduction in light emission efficiency, no transmission error due to insufficient light emission current, a small circuit area, and low power consumption (for example, see Patent Document 1).

  FIG. 15 shows a block diagram of a main part of a digital isolator 100 conventionally used. In the figure, 1 is a primary side circuit, 2 is a secondary side circuit, and the primary side circuit 1 operates by receiving the supply of the power supply voltage VDD1 from the input side power supply 3, and the secondary side circuit 2 outputs. The power supply voltage VDD2 from the side power supply 4 is supplied to operate.

  The primary side circuit 1 includes a quantization unit (logic conversion unit) 1-1, a transmission unit 1-2, and an update pulse generation unit 1-3. The secondary side circuit 2 includes a reception unit 2-1. An output unit 2-2 and an update pulse monitoring unit (fail-safe circuit) 2-3 are provided, and between the transmission unit 1-2 of the primary side circuit 1 and the reception unit 2-1 of the secondary side circuit 2. An insulating part 5 is provided.

[Normal operation]
In this digital isolator 100, the input signal terminal TIN of the primary side circuit 1 is supplied with a digital signal DIN whose signal level changes between “H” level and “L” level as an input signal (FIG. 16). (See (a)). The quantization unit 1-1 receives the change in the signal level of the input signal DIN, converts it to a logic signal of “H” / “L” level, and sends it to the transmission unit 1-2.

  The signal transmitted to the transmission unit 1-2 is received by the reception unit 2-1 of the secondary circuit 2 through the insulating unit 5, and is transmitted to the output unit 2-2. The output unit 2-2 outputs the signal sent from the receiving unit 2-1 as an output signal DOUT from the secondary circuit 2 from the output signal terminal TOUT (see FIG. 16B).

  16C shows the supply state of the power supply voltage VDD1 from the input side power supply 3 to the primary side circuit 1, and FIG. 16D shows the power supply from the output side power supply 4 to the secondary side circuit 2. The supply state of the voltage VDD2 is shown, and the power supply voltages VDD1 and VDD2 are always supplied to the primary side circuit 1 and the secondary side circuit 2.

[Fail-safe operation]
During the normal operation described above, the update pulse generator 1-3 in the primary circuit 1 monitors the signal from the quantizer 1-1 to the transmitter 1-2, and this signal changes over a certain time. If not, an update pulse is output to the transmission unit 1-2. This update pulse is transmitted from the transmission unit 1-2 to the reception unit 2-1 of the secondary circuit 2 through the insulating unit 5.

  The update pulse monitoring unit 2-3 monitors the update pulse received by the reception unit 2-1. When the update pulse is not received, the power supply voltage VDD1 to the primary side circuit 1 is cut off or the primary side circuit 1 is determined to be in a non-operating state, and the output signal DOUT from the output unit 2-2, that is, the output signal DOUT from the secondary side circuit 2, is forcibly fixed to the "H" level or the "L" level.

  FIG. 17 shows a time chart when the power supply voltage VDD1 to the primary side circuit 1 is cut off. In this example, the power supply voltage VDD1 to the primary circuit 1 is cut off at the point t1 (FIG. 17C: point t1), and the output signal DOUT from the secondary circuit 2 is forcibly set to “H”. ”Level (FIG. 17B: point t1). As an opposite method, as shown in FIG. 18, the output signal DOUT from the secondary circuit 2 may be forcibly fixed to the “L” level.

  FIG. 19 shows an input / output truth table including the operation of the digital isolator 100 in fail-safe mode. As can be seen from this truth table, when the power supply voltage VDD1 to the primary circuit 1 is cut off, the output signal DOUT is set to the “H” level or the “L” level regardless of the signal level of the input signal DIN. Forced to be fixed.

  FIG. 20 shows a diagram in the case where the digital isolator 100 is configured by one IC (integrated circuit). In the integrated circuit IC1 constituting the digital isolator 100, the primary side pin P1 and the pin P3 are internally connected, the power supply voltage VDD1 is applied to the pin P1, and the input signal DIN is applied to the pin P2. . This pin P2 is used as the input signal terminal TIN of the digital isolator 100.

  The pin P4 is grounded, and a capacitor C1 is connected between the pins P3 and P4. Also, the secondary side pins P6 and P8 are internally connected, and the power supply voltage VDD2 is applied to the pin P5, and the output signal DOUT is obtained from the pin P7. This pin P7 is used as the output signal terminal TOUT of the digital isolator 100. The pin P8 is grounded, and a capacitor C2 is connected between the pins P5 and P6.

JP 2007-123650 A

  When such a digital isolator is used in a two-wire field device, power consumption can be reduced. However, in a 2-wire field device, there is a great restriction on the operating power, so even if a low power consumption type digital isolator is adopted, there is no surplus power unless the control cycle is lengthened. If the length is increased, the controllability is reduced. For this reason, further reduction in power consumption is required for digital isolators.

  The present invention has been made to solve such a problem, and an object thereof is to provide a digital isolator capable of further reducing power consumption and a field device using the digital isolator. It is in.

  In order to achieve such an object, a digital isolator according to the present invention includes a primary circuit that operates by receiving a first power supply and a secondary circuit that operates by receiving a second power supply. The digital signal whose signal level changes between the first level and the second level is used as an input signal, and the input signal is sent to the secondary circuit without contact through the primary circuit. While the output signal from the secondary side circuit is used, when the supply of the first power supply to the primary side circuit is interrupted, the level of the output signal from the secondary side circuit is either the first level or the second level. In the digital isolator forcibly fixed to one level, there is provided switch means for turning on / off the supply of the first power to the primary side circuit according to the level of the input signal, and the input signal terminal of the primary side circuit Instead of the input signal to the primary circuit The level of the output signal from the secondary circuit to be forcibly fixed at the time the supply interruption of the first power source is obtained by the so adversely level signal.

  In the present invention, for example, the first level is “H” level, the second level is “L” level, and the secondary side circuit that is forcibly fixed when the supply of the first power to the primary side circuit is cut off. When the level of the output signal from H is set to "H" level, the supply of the first power to the primary side circuit is turned on / off according to the level of the input signal, while the input signal terminal of the primary side circuit Instead of the input signal, an “L” level input signal is input.

  In this case, when the supply of the first power supply to the primary circuit is turned on according to the level of the input signal, the “L” level input signal input to the input signal terminal of the primary circuit is It is sent to the secondary circuit without contact and is output as an output signal from the secondary circuit. On the other hand, when the supply of the first power supply to the primary side circuit is turned off according to the level of the input signal, the level of the output signal from the secondary side circuit is fixed to the “H” level. As a result, the level of the output signal from the secondary side circuit is “L” / “H” according to on / off of the supply of the first power supply to the primary side circuit, that is, according to the level of the input signal. Change to level. In this case, the first power is supplied to the primary side circuit only when the “L” level signal is transmitted, and when the “H” level signal is transmitted, the first power is supplied to the primary side circuit. Since the power supply of 1 is cut off, power consumption in the primary side circuit is reduced.

  In the present invention, for example, the first level is the “H” level, the second level is the “L” level, and the secondary is forcibly fixed when the supply of the first power to the primary circuit is shut off. When the level of the output signal from the side circuit is “L” level, the supply of the first power to the primary side circuit is turned on / off according to the level of the input signal, while the input of the primary side circuit Instead of an input signal, an “H” level input signal is input to the signal terminal.

  In this case, when the supply of the first power supply to the primary circuit is turned on according to the level of the input signal, the “H” level input signal input to the input signal terminal of the primary circuit is It is sent to the secondary circuit without contact and is output as an output signal from the secondary circuit. On the other hand, when the supply of the first power supply to the primary side circuit is turned off according to the level of the input signal, the level of the output signal from the secondary side circuit is fixed to the “L” level. As a result, the level of the output signal from the secondary side circuit is “H” / “L” according to on / off of the supply of the first power supply to the primary side circuit, that is, according to the level of the input signal. Change to level. In this case, the first power is supplied to the primary side circuit only when the “H” level signal is transmitted, and when the “L” level signal is transmitted, the first power is supplied to the primary side circuit. Since the power supply of 1 is cut off, power consumption in the primary side circuit is reduced.

  In the present invention, instead of an input signal at the input signal terminal of the primary circuit, the level of the output signal from the secondary circuit that is forcibly fixed when the supply of the first power to the primary circuit is cut off. Gives a signal of the opposite level, but the switch means may always give a signal of the opposite level regardless of whether the first power supply to the primary side circuit is turned on or off. The reverse level signal may be given only while the first power supply to the primary circuit is turned on.

  Also, a signal holding circuit for holding the output signal from the secondary side circuit is provided, and the signal is sent when the level of the signal sent to the secondary side circuit through the primary side circuit in a non-contact manner is the same as the previous time. You may make it provide the signal output stop means to stop an output.

  Further, a digital isolator according to the present invention receives a signal in a predetermined current range sent from a host control device via a pair of electric wires, and generates an operation power supply circuit from this signal, A control unit that receives a supply of operation power generated by the operation power supply circuit and performs a predetermined operation, a communication circuit for transmitting information from the control unit to an external device, and an intervening unit between the control unit and the communication circuit For example, it is used as an isolator in a valve positioner (electropneumatic positioner) as a field device including an isolator that ensures electrical insulation. The field device using the digital isolator according to the present invention is not limited to the valve positioner, and may be used as an isolator in a two-wire electromagnetic flow meter, a two-wire temperature transmitter, or the like.

  According to the present invention, the switch means for turning on / off the supply of the first power to the primary circuit according to the level of the input signal is provided, and the input signal terminal of the primary circuit is replaced with the input signal, Since a signal having a level opposite to the level of the output signal from the secondary side circuit that is forcibly fixed when the supply of the first power supply to the primary side circuit is cut off, the signal to the primary side circuit is supplied. By transmitting a signal to the secondary circuit while intermittently shutting off the first power supply, it is possible to reduce power consumption in the primary circuit and further reduce power consumption.

It is a block diagram which shows the principal part of one Embodiment (Embodiment 1) of the digital isolator which concerns on this invention. 3 is a time chart for explaining the operation of the digital isolator of the first embodiment. It is a figure at the time of comprising the digital isolator of this Embodiment 1 by two IC (integrated circuit). It is a block diagram which shows the principal part of other Embodiment (Embodiment 2) of the digital isolator which concerns on this invention. It is a time chart for demonstrating operation | movement of the digital isolator of this Embodiment 2. FIG. It is a figure at the time of comprising the digital isolator of this Embodiment 2 with two IC (integrated circuit). FIG. 7 is a diagram showing a modification (Embodiment 3) of the digital isolator shown in FIG. 6. It is a time chart for demonstrating operation | movement of the digital isolator of this Embodiment 3. FIG. 8 is a diagram showing a modification (Embodiment 4) of the digital isolator shown in FIG. 7. It is a time chart for demonstrating operation | movement of the digital isolator of this Embodiment 4. FIG. 11 is a diagram illustrating an example (fifth embodiment) in which a signal holding circuit that holds an output signal from a secondary circuit is provided. It is a figure which shows the example (Embodiment 6) which used the digital isolator which concerns on this invention for the 2-wire type field apparatus (valve positioner). It is a figure which shows the example (Embodiment 7) which used the digital isolator which concerns on this invention for the 2-wire type field apparatus (2-wire type electromagnetic flowmeter). It is a figure which shows the example (Embodiment 8) which used the digital isolator which concerns on this invention for a 2-wire type field apparatus (2-wire type temperature transmitter). It is a block diagram of the principal part of the digital isolator conventionally used. It is a time chart for demonstrating normal operation | movement of the conventional digital isolator. It is a time chart for demonstrating the operation | movement (example which forcibly fixes an output signal to "H" level) at the time of fail safe of the conventional digital isolator. It is a time chart for demonstrating the operation | movement (example which forcibly fixes an output signal to "L" level) at the time of fail safe of the conventional digital isolator. It is a figure which shows the truth table of input / output including the operation | movement at the time of fail safe of the conventional digital isolator. It is a figure at the time of comprising the conventional digital isolator by one IC (integrated circuit).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Embodiment 1]
FIG. 1 is a block diagram showing a main part of an embodiment (Embodiment 1) of a digital isolator according to the present invention. In the figure, the same reference numerals as those in FIG. 15 denote the same or equivalent components as those described with reference to FIG. The digital isolator according to the first embodiment is denoted by reference numeral 101.

  The digital isolator 101 is different from the conventional digital isolator 100 in that a switch unit 6 is provided between the input-side power supply 3 and the primary-side circuit 1, and is conventionally applied to the input signal terminal TIN of the primary-side circuit 1. The input signal DIN which has been set is supplied to the switch unit 6 and the switch unit 6 is turned on / off according to the level of the input signal DIN. Further, the level of the output signal DOUT from the secondary circuit 2 that is forcibly fixed when the supply of the power supply voltage VDD1 to the primary circuit 1 is cut off at the input signal terminal TIN instead of the input signal DIN. It is in the place where the signal of the level is always given.

  In this example, the level of the output signal DOUT from the secondary circuit 2 is forcibly fixed to the “H” level when the supply of the power supply voltage VDD1 to the primary circuit 1 is cut off. The switch unit 6 is turned on when the input signal DIN becomes “L” level, and turned off when the input signal DIN becomes “H” level. Further, the input signal terminal TIN of the primary side circuit 1 has an "L" level signal as a signal having a level opposite to the level of the output signal DOUT when the supply voltage VDD1 to the primary side circuit 1 is cut off. It is assumed that a signal is always given.

  In the digital isolator 101, an input signal DIN is supplied to the switch unit 6, and the switch unit 6 is turned on / off according to the level of the input signal DIN. In this case, when the input signal DIN becomes “L” level, the switch unit 6 is turned on, and the power supply voltage VDD 1 is supplied to the primary side circuit 1. When the input signal DIN becomes “H” level, the switch unit 6 is turned off, and the supply of the power supply voltage VDD1 to the primary side circuit 1 is cut off.

  When the input signal DIN becomes “L” level (point t1 shown in FIG. 2 (a)) and the power supply voltage VDD1 is supplied to the primary circuit 1 (point t1 shown in FIG. 2 (f)), input is performed. An “L” level signal applied to the signal terminal TIN is sent to the transmitter 1-2.

  The “L” level signal sent to the transmission unit 1-2 is received by the reception unit 2-1 of the secondary circuit 2 through the insulation unit 5, and is transmitted to the output unit 2-2. The output unit 2-2 outputs the “L” level signal sent from the receiving unit 2-1 from the output signal terminal TOUT as the output signal DOUT from the secondary side circuit 2 (FIG. 2B). T1 point shown).

  When the input signal DIN becomes “H” level (point t2 shown in FIG. 2A), supply of the power supply voltage VDD1 to the primary circuit 1 is cut off (point t2 shown in FIG. 2F). The update pulse monitoring unit 2-3 of the secondary side circuit 2 forcibly fixes the output signal DOUT from the secondary side circuit 2 to the “H” level (point t2 shown in FIG. 2B).

  In the same manner, the output from the secondary side circuit 1 according to on / off of the supply of the power supply voltage VDD1 to the primary side circuit 1, that is, according to the “L” / “H” level of the input signal DIN. The level of the signal DOUT changes to “L” / “H” level.

  In this case, the power supply voltage VDD1 is supplied to the primary circuit 1 only when an “L” level signal is transmitted, and to the primary circuit 1 when an “H” level signal is transmitted. Since the supply of the power supply voltage VDD1 is cut off, the power consumption in the primary side circuit 1 is reduced. As a result, power consumption can be further reduced compared to the conventional digital isolator 100 (FIG. 15) that constantly supplies the power supply voltage VDD1 to the primary side circuit 1.

  FIG. 3 shows a diagram in the case where the digital isolator 101 is composed of two ICs (integrated circuits). The digital isolator 101 includes the conventional integrated circuit IC1 shown in FIG. 20 and the integrated circuit IC2 that functions as the switch unit 6 in FIG.

  The integrated circuit IC2 includes pins P9 to P14, and the connection state between the pin P13, the pin P12, and the pin 14 is selectively switched internally. In this example, the power supply voltage VDD1 is applied to the pin P10 and the pin P12, and the input signal DIN is applied to the pin P9. When the level of the input signal DIN becomes “L” level, the pin P13 is connected to the pin P12 side. When the input signal DIN becomes “H” level, the pin P13 is connected to the pin P14 side. A capacitor C3 is connected between the pin P10 and the pin P11, and the pin P14 is grounded.

  Further, the integrated circuit IC1 and the integrated circuit IC2 are connected by inserting a resistor R1 between the pin P1 of the integrated circuit IC1 and the pin P13 of the integrated circuit IC2. Further, the integrated circuit IC1 is of a type in which the level of the output signal DOUT from the pin P7 (output signal terminal TOUT) is forcibly fixed to the “H” level when the supply of the power supply voltage VDD1 to the pin P1 is cut off. Yes. Further, the pin P2 (input signal terminal TIN) provided for inputting the input signal DIN of the integrated circuit IC1 is grounded through the resistor R2.

  That is, instead of applying the input signal DIN to the input signal terminal TIN of the integrated circuit IC1, the signal of the “L” level (the output signal DOUT that is forcibly fixed when the supply of the power supply voltage VDD1 is cut off is opposite to the level). Level signal). As a result, the level of the input signal terminal TIN of the integrated circuit IC1 is always fixed to the “L” level, and the same operation as described with reference to FIG. 2 is obtained.

[Embodiment 2]
In the first embodiment, the level of the output signal DOUT from the secondary circuit 2 is forcibly fixed to the “H” level when the supply voltage VDD1 to the primary circuit 1 is cut off. In the second embodiment, it is assumed that the level of the output signal DOUT from the secondary circuit 2 is forcibly fixed to the “L” level when the supply of the power supply voltage VDD1 to the primary circuit 1 is cut off.

  In this case, as shown in FIG. 4, the output from the secondary circuit 2 that is forcibly fixed to the input signal terminal TIN of the primary circuit 1 when the supply of the power supply voltage VDD1 to the primary circuit 1 is cut off. It is assumed that an “H” level signal is always given as a signal having a level opposite to that of the signal DOUT. Further, the switch unit 6 is turned on when the input signal DIN becomes “H” level, and is turned off when the input signal DIN becomes “L” level. The digital isolator according to the second embodiment is denoted by reference numeral 102.

  In this digital isolator 102, an input signal DIN is supplied to the switch unit 6, and the switch unit 6 is turned on / off according to the level of the input signal DIN. In this case, when the input signal DIN becomes “H” level, the switch unit 6 is turned on and the power supply voltage VDD 1 is supplied to the primary side circuit 1. When the input signal DIN becomes “L” level, the switch unit 6 is turned off, and the supply of the power supply voltage VDD1 to the primary side circuit 1 is cut off.

  When the input signal DIN becomes “H” level (point t1 shown in FIG. 5 (a)) and the power supply voltage VDD1 is supplied to the primary circuit 1 (point t1 shown in FIG. 5 (f)), input is performed. An “H” level signal applied to the signal terminal TIN is sent to the transmitter 1-2.

  The “H” level signal sent to the transmission unit 1-2 is received by the reception unit 2-1 of the secondary circuit 2 through the insulation unit 5, and is sent to the output unit 2-2. The output unit 2-2 outputs the “H” level signal sent from the receiving unit 2-1 from the output signal terminal TOUT as the output signal DOUT from the secondary circuit 2 (see FIG. 5B). T1 point shown).

  When the input signal DIN becomes the “L” level (point t2 shown in FIG. 5A), the supply of the power supply voltage VDD1 to the primary circuit 1 is cut off (point t2 shown in FIG. 5F). The update pulse monitoring unit 2-3 of the secondary side circuit 2 forcibly fixes the output signal DOUT from the secondary side circuit 2 to the “L” level (point t2 shown in FIG. 5B).

  In the same manner, the output from the secondary side circuit 1 according to on / off of the supply of the power supply voltage VDD1 to the primary side circuit 1, that is, according to the “H” / “L” level of the input signal DIN. The level of the signal DOUT changes to “H” / “L” level.

  In this case, the power supply voltage VDD1 is supplied to the primary side circuit 1 only when the “H” level signal is transmitted, and when the “L” level signal is transmitted, the primary side circuit 1 is supplied. Since the supply of the power supply voltage VDD1 is cut off, the power consumption in the primary side circuit 1 is reduced. As a result, power consumption can be further reduced compared to the conventional digital isolator 100 (FIG. 15) that constantly supplies the power supply voltage VDD1 to the primary side circuit 1.

  FIG. 6 shows a diagram in the case where the digital isolator 102 is composed of two ICs (integrated circuits). The digital isolator 102 includes the conventional integrated circuit IC1 shown in FIG. 20 and the integrated circuit IC2 serving as the switch unit 6 in FIG.

  The integrated circuit IC2 includes pins P9 to P14, and the connection state between the pin P13, the pin P12, and the pin P14 is selectively switched internally. In this example, the power supply voltage VDD1 is applied to the pin P10 and the pin P12, and the input signal DIN is applied to the pin P9. When the level of the input signal DIN becomes “H” level, the pin P13 is connected to the pin P12 side. When the input signal DIN becomes “L” level, the pin P13 is connected to the pin P14 side. A capacitor C3 is connected between the pin P10 and the pin P11, and the pin P14 is grounded.

  Further, the integrated circuit IC1 and the integrated circuit IC2 are connected by inserting a resistor R1 between the pin P1 of the integrated circuit IC1 and the pin P13 of the integrated circuit IC2. Further, when the supply of the power supply voltage VDD1 to the pin P1 is cut off, the integrated circuit IC1 forcibly fixes the level of the output signal DOUT from the pin P7 (output signal terminal TOUT) of the integrated circuit IC1 to the “L” level. It is a type. The power supply voltage VDD1 is always applied to the pin P2 (input signal terminal TIN) provided for inputting the input signal DIN of the integrated circuit IC1.

  That is, instead of giving the input signal DIN to the input signal terminal TIN of the integrated circuit IC1, the signal of the “H” level is always reversed (opposite to the level of the output signal DOUT that is forcibly fixed when the supply of the power supply voltage VDD1 is cut off). Level signal). As a result, the level of the input signal terminal TIN of the integrated circuit IC1 is always fixed to the “H” level, and the same operation as described with reference to FIG. 5 is obtained.

[Embodiment 3]
In FIG. 6, an "H" level signal is always applied to the input signal terminal TIN of the integrated circuit IC1, but as shown in FIG. 7, the pin P13 of the integrated circuit IC2 and the input signal terminal TIN of the integrated circuit IC1 May be directly connected to each other, and the level of the signal generated at the pin P13 may be given to the input signal terminal TIN. This digital isolator is denoted by reference numeral 103 as Embodiment 3.

  In this digital isolator 103, the input signal DIN is applied to the pin P9 of the integrated circuit IC2, and the connection state between the pin P13, the pin P12 and the pin P14 is selectively switched according to the level of the input signal DIN. In this case, when the input signal DIN becomes “H” level, the pin P13 is connected to the pin P12 side, and the power supply voltage VDD1 is supplied to the pin P1 of the integrated circuit IC1.

  At this time, an “H” level signal is given to the input signal terminal TIN of the integrated circuit IC1 through the pin P13 of the integrated circuit IC2. When the input signal DIN becomes “L” level, the pin P13 is connected to the pin P14, and the supply of the power supply voltage VDD1 to the pin P1 of the integrated circuit IC1 is cut off. At this time, an “L” level signal is applied to the input signal terminal TIN of the integrated circuit IC1 through the pin P13 of the integrated circuit IC2.

  When the input signal DIN becomes the “H” level (point t1 shown in FIG. 8A) and the power supply voltage VDD1 is supplied to the pin P1 of the integrated circuit IC1 (point t1 shown in FIG. 8F), The “H” level signal (FIG. 8E) applied to the input signal terminal TIN of the integrated circuit IC1 is sent to the secondary side and output as the output signal DOUT (t1 shown in FIG. 8B). point).

  When the input signal DIN becomes “L” level (point t2 shown in FIG. 8A) and the supply of the power supply voltage VDD1 to the pin P1 of the integrated circuit IC1 is cut off (t2 shown in FIG. 8F). On the other hand, the output signal DOUT is forcibly fixed to the “L” level by the fail-safe function of the integrated circuit IC1 (point t2 shown in FIG. 8B).

  Similarly, in accordance with the on / off of the supply of the power supply voltage VDD1 to the pin P1 of the integrated circuit IC1, that is, according to the “H” / “L” level of the input signal DIN to the pin P9 of the integrated circuit IC2. The level of the output signal DOUT changes to “H” / “L” level.

  In this way, only while the power supply voltage VDD1 is being supplied to the pin P1 of the integrated circuit IC1, an “H” level signal (forced when the supply of the power supply voltage VDD1 is cut off) is applied to the input signal terminal TIN of the integrated circuit IC1. Even if a signal having a level opposite to the level of the fixed output signal DOUT is given, the same operation as in the second embodiment can be performed.

[Embodiment 4]
In the third embodiment, the pin P13 of the integrated circuit IC2 and the input signal terminal TIN of the integrated circuit IC1 are directly connected. However, as shown in FIG. 9, the pin P13 of the integrated circuit IC2 and the integrated circuit IC1 May be connected via an inverter INV1. In this case, the integrated circuit IC1 is of a type in which the level of the output signal DOUT from the output signal terminal TOUT is forcibly fixed to the “H” level when the supply voltage VDD1 to the input signal terminal TIN is cut off. . This digital isolator is denoted by reference numeral 104 as a fourth embodiment.

  In this digital isolator 104, the input signal DIN is applied to the pin P9 of the integrated circuit IC2, and the connection state between the pin P13, the pin P12 and the pin P14 is selectively switched according to the level of the input signal DIN. In this case, when the input signal DIN becomes “L” level, the pin P13 is connected to the pin P12 side, and the power supply voltage VDD1 is supplied to the pin P1 of the integrated circuit IC1.

  At this time, an “L” level signal is given to the input signal terminal TIN of the integrated circuit IC1 through the pin P13 of the integrated circuit IC2 and the inverter INV1. When the input signal DIN becomes “H” level, the pin P13 is connected to the pin P14 side, and the supply of the power supply voltage VDD1 to the pin P1 of the integrated circuit IC1 is cut off. At this time, an “H” level signal is applied to the input signal terminal TIN of the integrated circuit IC1 through the pin P13 of the integrated circuit IC2 and the inverter INV1.

  When the input signal DIN becomes “L” level (point t1 shown in FIG. 10A) and the power supply voltage VDD1 is supplied to the pin P1 of the integrated circuit IC1 (point t1 shown in FIG. 10F), An “L” level signal (FIG. 10E) applied to the input signal terminal TIN of the integrated circuit IC1 is sent to the secondary side and output as an output signal DOUT (t1 shown in FIG. 10B). point).

  When the input signal DIN becomes the “H” level (point t2 shown in FIG. 10A) and the supply of the power supply voltage VDD1 to the pin P1 of the integrated circuit IC1 is cut off (t2 shown in FIG. 10F). On the other hand, the output signal DOUT is forcibly fixed to the “H” level by the fail-safe function of the integrated circuit IC1 (point t2 shown in FIG. 10B).

  Similarly, in accordance with the on / off of the supply of the power supply voltage VDD1 to the pin P1 of the integrated circuit IC1, that is, according to the “L” / “H” level of the input signal DIN to the pin P9 of the integrated circuit IC2. The level of the output signal DOUT changes to “L” / “H” level.

  In this way, only while the power supply voltage VDD1 is being supplied to the pin P1 of the integrated circuit IC1, an “L” level signal (forcibly when the supply of the power supply voltage VDD1 is cut off) is applied to the input signal terminal TIN of the integrated circuit IC1. Even if a signal having a level opposite to the level of the fixed output signal DOUT is given, the same operation as in the first embodiment can be performed.

[Embodiment 5]
FIG. 11 shows an example in which a signal holding circuit for holding an output signal from the secondary circuit is provided as the fourth embodiment. In the digital isolator 105 of the fifth embodiment, in addition to the configuration of the digital isolator 101 shown in the first embodiment, a signal holding circuit 7 that holds the output signal DOUT from the secondary side circuit 2 is provided. Further, the level of the signal sent from the primary side circuit 1 to the secondary side circuit 2 in a non-contact manner is compared with the level of the previous signal, and a signal is output when the level of the signal is the same as the previous level. Is provided with a signal output stop section 2-4.

  In this digital isolator 105, since the output signal DOUT from the secondary side circuit 2 is held by the signal holding circuit 7, the level of the signal sent from the primary side circuit 1 in a non-contact manner remains the same as the previous time. For example, energy output can be saved by stopping the output of the signal by the signal output stop unit 2-4.

  It should be noted that not only the first embodiment but also the second to fourth embodiments may have a configuration in which the signal holding circuit 7 and the signal output stop unit 2-4 are provided.

[Embodiment 6]
FIG. 12 shows an example in which the digital isolator according to the present invention is used in a two-wire field device. In this example, an application example to a valve positioner (electro-pneumatic positioner) is shown as a two-wire field device.

  In the figure, 200 is a valve positioner, 300 is a host controller, 400 is a valve, 500 is an external power source, and 600 is an external device such as a personal computer. The valve positioner 200 includes a signal input block 201, a power supply block 202, a control unit 203, an opening adjustment unit (electro-pneumatic conversion unit) 204, an opening detection sensor 205, a communication circuit 206, and a digital isolator 207. It has.

  In the valve positioner 200, the signal input block 201 receives a control signal current that changes in a current range of 4 to 20 mA sent from the host control device 300 via a pair of electric wires. The power supply block 202 generates its own operating power supply from the control signal current received by the signal input block 201 and supplies it to the control unit 203 and the digital isolator 207.

  The control unit 203 receives the operation power generated by the power supply block 202, and uses the control signal current value from the signal input block 201 as an opening signal from the host controller 300 through the opening adjustment unit 204. The opening degree of 400 is controlled. This opening degree control is performed by the control block 203A in the control unit 203.

  The control unit 203 (output block 203B, communication block 203C) performs abnormality diagnosis of the valve 400, self-abnormality diagnosis, and the like, and sends the diagnosis result and actual valve opening (opening signal) to the external device 600. The data is output via the communication circuit 206 (output block 206A, communication block 206B).

  The diagnosis result and the opening signal are output to the external device 600 by a current signal of 4 to 20 mA. However, since the output from the host controller 300 supplied to the valve positioner 200 is insufficient, A current is supplied from the power source 500. At this time, in order to ensure electrical insulation between the communication circuit 206 and the control unit 203, a digital isolator 207 is interposed between the communication circuit 206 and the control unit 203.

  In the present embodiment, the digital isolators 101 to 105 shown as the first to fifth embodiments are used as the digital isolators 207 interposed between the communication circuit 206 and the control unit 203.

  As a result, the power consumption in the digital isolator 207 is reduced, and the reduction in the power consumption is allocated to the control unit 203 and the like, thereby improving controllability and adding other functions. In addition, it is possible to avoid power shortage during communication with the external device 600 and sacrifice of the control operation of the valve 400.

[Embodiment 7]
FIG. 13 shows another example in which the digital isolator according to the present invention is used in a two-wire field device. In this example, an application example to a two-wire electromagnetic flow meter is shown as a two-wire field device.

  The two-wire electromagnetic flowmeter 700 includes a conversion unit 701 and a detector 702. The conversion unit 701 includes a power supply block 703, a transformer 704, a power supply (analog) 705, a digital circuit unit (microcomputer) 706, , A digital isolator 707, a timing block 708, a sampling circuit block 709, a signal processing circuit block 710, a digital isolator (level shift) 711, and a timing block 712, and a detector 702 includes an electrode unit 713, A coil portion 714. The electrode part 713 is exposed to a fluid, and an exciting current is supplied to the coil part 714.

  In this two-wire electromagnetic flowmeter 700, the fluid side of the detector 702 has a pipe ground as a reference potential, the potential is different from the ground of the external power supply 500, and the electromotive force signal from the fluid is based on the pipe ground. Since the signal processing described above has an effect on the fluid noise processing, the fluid side and the external power source 500 side need to be isolated. For this purpose, a digital isolator 707 is interposed between the digital circuit unit 706 and the timing block 708. In addition, since the coil unit 714 side of the detector 702 has a series connection system in which the coil power source is higher and the circuit power source is lower for efficiency of current consumption, the level is between the digital circuit unit 706 and the timing block 712. A shift digital isolator 711 is interposed. In the present embodiment, digital isolators 101 to 105 shown as the first to fifth embodiments are used as the digital isolators 707 and 711.

[Embodiment 8]
FIG. 14 shows another example in which the digital isolator according to the present invention is used in a two-wire field device. In this example, an application example to a two-wire temperature transmitter is shown as a two-wire field device.

  The two-wire temperature transmitter 800 includes a circuit block 801 and a temperature sensor unit 802. The circuit block 801 includes a power supply block 803, a transformer 804, a power supply (analog) 805, and a digital circuit unit (microcomputer) 806. A digital isolator 807, a timing block 808, and a signal processing circuit block 809, and the temperature sensor unit 802 includes an electrode unit 810. The electrode part 810 is exposed to fluid.

  In the two-wire temperature transmitter 800, the temperature sensor unit 802 may be installed at the ground on the process side, and therefore, isolation from the ground of the external power source 500 is required. For this purpose, a digital isolator 807 is interposed between the digital circuit unit 806 and the timing block 808. In this embodiment, as this digital isolator 807, the digital isolators 101 to 105 shown as the first to fifth embodiments are used.

  The digital isolator of the present invention is a digital isolator that ensures electrical insulation of input / output signals between a primary side circuit and a secondary side circuit, such as between a control unit and a communication circuit in a two-wire field device. It can be used in various fields.

  DESCRIPTION OF SYMBOLS 1 ... Primary side circuit, 1-1 ... Quantization part (logic conversion part), 1-2 ... Transmission part, 1-3 ... Update pulse generation part, 2 ... Secondary side circuit, 2-1 ... Reception part, 2-2 ... Output unit, 2-3 ... Update pulse monitoring unit (fail safe circuit), 2-4 ... Signal output stop unit, 3 ... Input side power source, 4 ... Output side power source, 5 ... Insulating unit, 6 ... Switch 7, signal holding circuit, TIN, input signal terminal, DIN, input signal, TOUT, output signal terminal, DOUT, output signal, IC 1, IC 2, integrated circuit, P 1 to P 14, pins, R 1, R 2, resistance, C 1 , C2, C3 ... capacitor, INV1 ... inverter, 101-105 ... digital isolator, 200 ... valve positioner, 201 ... signal input block, 202 ... power supply block, 203 ... control unit, 203A ... control block, 203B ... output block, 203C ... communication 204: Opening adjustment unit, 205 ... Opening detection sensor, 206 ... Communication circuit, 206A ... Output block, 206B ... Communication block, 207 ... Digital isolator, 300 ... High-order control device, 400 ... Valve, 500 ... External power source, 600 ... external device, 700 ... 2-wire electromagnetic flow meter, 701 ... conversion unit, 702 ... detector, 703 ... power supply block, 704 ... transformer, 705 ... power source (for analog), 706 ... digital circuit unit ( Microcomputer), 707 ... digital isolator, 708 ... timing block, 709 ... sampling circuit block, 710 ... signal processing circuit block, 711 ... digital isolator (level shift), 712 ... timing block, 713 ... electrode part, 714 ... coil part, 800 ... Two-wire temperature transmitter, 801 ... Circuit block 802 ... Temperature sensor unit, 803 ... Power supply block, 804 ... Transformer, 805 ... Power supply (for analog), 806 ... Digital circuit unit (microcomputer), 807 ... Digital isolator, 808 ... Timing block, 809 ... Signal processing circuit block, 810 ... electrode part.

Claims (8)

A primary side circuit that operates in response to the supply of the first power supply; and a secondary side circuit that operates in response to the supply of the second power supply, the signal levels of which are the first level and the second level. A digital signal that changes between the two is used as an input signal, and the input signal is sent to the secondary circuit without contact through the primary circuit and is used as an output signal from the secondary circuit. In a digital isolator that forcibly fixes the level of the output signal from the secondary side circuit to one of the first and second levels when the supply of the first power source to is interrupted ,
Switch means for turning on / off the supply of the first power to the primary circuit according to the level of the input signal;
The primary circuit is
An input signal terminal provided for input of the input signal;
Instead of the input signal at the input signal terminal of the primary side circuit, an output signal from the secondary side circuit that is forcibly fixed when the supply of the first power to the primary side circuit is cut off. A digital isolator characterized in that a signal with a level opposite to the level is given. The digital isolator according to claim 1, wherein
Regardless of whether the first power supply to the primary circuit is turned on or off by the switch means, the signal of the opposite level is always given to the input signal terminal of the primary circuit. A digital isolator. The digital isolator according to claim 1, wherein
The reverse level signal is applied to the input signal terminal of the primary side circuit only while the switch means is turning on the supply of the first power to the primary side circuit. Digital isolator. The digital isolator according to any one of claims 1 to 3,
The first level is an “H” level;
The second level is an “L” level;
The level of the output signal from the secondary circuit that is forcibly fixed when the supply of the first power to the primary circuit is cut off is an “H” level. The digital isolator according to any one of claims 1 to 3,
The first level is an “H” level;
The second level is an “L” level;
The digital isolator characterized in that the level of the output signal from the secondary side circuit that is forcibly fixed when the supply of the first power to the primary side circuit is cut off is "L" level. The digital isolator according to any one of claims 1 to 3,
A signal holding circuit for holding an output signal from the secondary circuit;
The secondary circuit is
A digital isolator comprising signal output stopping means for stopping signal output when the level of a signal sent in a non-contact manner through the primary circuit is the same as the previous level. An operation power supply circuit that receives a signal in a predetermined current range sent from the host controller via a pair of electric wires and generates its own operation power from this signal, and supply of the operation power generated by this operation power supply circuit Received from the control unit, a communication circuit for transmitting information from the control unit to an external device, and interposed between the control unit and the communication circuit to ensure electrical insulation. In field devices equipped with isolators,
The field device according to claim 1, wherein the isolator is the digital isolator according to claim 1. In the field device according to claim 7,
The field device is a valve positioner.

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