JPH04205202A - Field device - Google Patents

Abstract

PURPOSE:To perform fail-safe operation without using any mechanical means by placing a reception part in the fail-safe operation with the electric power supplied from a transmission part when a set value signal to be inputted to the reception part is not inputted. CONSTITUTION:A current I normally flows when Vt>Vz, where Vt is the voltage between lines 6 and 7 between a controller 2 and the reception part 4 and Vz is the voltage drop across a Zener diode ZD. At this time, the current (i) from a voltage source Vp flows as a loop current through a line 8 and the transmission part 5. If the lines 6 and 7 are broken or if the input current is ceased, the reception part 4 detects the abnormality and fully opens or closes, for example, a control valve 3 as the fail-safe operation. Consequently, the fail-safe function of an actuator can easily and optionally be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a field device used in plants and other systems to operate actuators such as control valves.

[Prior Art] Field devices include two-wire receivers, such as electro-pneumatic converters and electro-pneumatic positioners, to which control signals are input from a controller via a transmission path consisting of two lines. In this instrument, the operating energy is obtained from the received signal, so it is necessary to have a structure that is mechanically Neil-safe when the received signal, that is, the input signal is lost.

[Problems to be Solved by the Invention] However, when changing the direction of a mechanical failsafe, the mechanical structure itself must also be changed, which is complicated and time-consuming. Furthermore, since the receiver itself does not have operating energy, there is a problem in that even if an abnormality occurs, its operation cannot be controlled.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a field device that can perform fail-safe operation without resorting to mechanical means when there is no input signal to the receiving section.

[Means for Solving the Problems] The present invention includes a receiving section that receives a set value transmitted from a controller and performs a predetermined operation corresponding to the set value, and a receiving section that is connected to a power source to monitor the operating state of the receiving section. and a transmitting section that transmits a signal, and the receiving section is operated in a fail-safe manner by the power supplied from the transmitting section when a setting value that should be input to the receiving section is not input. Features.

[Function] In the present invention, power is supplied from the transmitting section to the receiving section, so if an abnormality such as loss of input signal to the receiving section occurs, the receiving section obtains the minimum operating energy from the transmitting section. Accordingly, actuators such as control valves can be caused to perform a preset fail-safe operation.

[Example] FIG. 1 shows the configuration of a field device according to the present invention.

The field device 1 controls an actuator (for example, controls the valve position of the control valve 3) in response to a control signal from the controller 2, and receives a set value transmitted from the controller 2, and performs control according to the set value. The receiving section 4 includes a receiving section 4 that performs predetermined operations, and a transmitting section 5 that transmits the operating state of the receiving section 4. A current signal (■) is input via the transmission line. On the other hand, a resistor R and a voltage source Vp are connected to the transmitter 5 by a line 8, and a current i flows through the line 8.

Further, the lines 6 and 8 are connected via a diode D, the lines 7 and 8 are also connected by a line 9, and a Zener diode Z is connected between the connection point of the line 8 and the lines 6 and 7.
D is connected.

The operation of the field device is as follows.

In FIG. 1, if the voltage across the line 6.7 between the controller 2 and the receiver 4 is Vt, and the voltage drop due to the Zener diode ZD is Vz, then if Vt>Vz, the current ■
is flowing normally. At this time, i is the line 8 and the transmitter 5
It flows as a loop current through the

Here, if the lines 6 and 7 are disconnected or the input current {circle around (2)} becomes O, the input of the receiver 4 enters a part of the current loop of the transmitter 5 through the line 9.

When the current generator disappears and the voltage Vt can no longer be generated in the receiving section 4, the loop current i is shunted to the Zener diode ZD and the receiving section 4. Due to this shunt, the receiver 4 detects an abnormality and performs a fail-safe operation such as fully opening or closing the control valve 3, for example.

FIG. 2 shows a positioner as an example of the field device of FIG.

The positioner 10 includes an input signal detection section 11 to which a control signal is input from the controller 2 via lines 6 and 7, a valve lift detection section 12 that detects the valve lift of the control valve 3, an input signal detection section 11, and a valve lift detection section 12 that detects the valve lift of the control valve 3. an arithmetic processing section 13 that performs predetermined arithmetic processing based on the detection signal from the lift detection section 12 and outputs a PWM signal (pulse width signal that gives a valve lift) that controls the drive section of the control valve 3; an electro-pneumatic conversion section 14 that converts the PWM output from the section 13 into a pneumatic signal and supplies it to the drive section of the control valve 3; and a communication processing section 15 that performs predetermined communication according to the signal output from the arithmetic processing section 13. Equipped with.

Note that since analog signals are output from the input signal detection section 11 and the valve lift detection section 12, an A/D converter 18 converts these signals into digital signals and inputs them to the arithmetic processing section 13.
is provided.

In the above configuration, a DC signal of I=4 to 20 mA is transmitted and received between the controller 2 and the input signal detection unit 11, and the controller 2
Power for operating the positioner 10 is supplied from. As the input signal detection section 11, a receiving device (Japanese Patent Laid-Open No. 60-257629) according to a patent application filed by the present applicant is used.

This receiving device inserts a first variable impedance element and a receiving impedance element in series in a two-wire transmission line, and makes the line voltage of the transmission line constant (for example, 10 volts). While controlling the impedance of the first variable impedance element in the direction, a series circuit of the second variable impedance element and the impedance element is connected in parallel, and a current flows through the impedance element. is configured to control the impedance of the second variable impedance element in a direction in which the impedance is constant (for example, 4 mA),
A load circuit is connected in parallel with the second variable impedance element. According to this configuration, the line electrician, or
In the case of ~20 mA, the current I flowing through the series circuit of the first variable impedance element and the receiving impedance element is set to only a signal component of O = 16 mA, without affecting the reception of the signal indicated by this current , it is possible to stably supply a maximum of 4 mA of power supply current to the load circuit.

In this way, the signal supplied from the controller 2 together with the power supply current is outputted from the input signal detection section 11 as a voltage signal of, for example, 1 to 3, by the load circuit, and is converted into a digital signal by the A/D converter 18 and calculated. The signal is supplied to the processing section 13.

On the other hand, the valve lift detection section 2 consists of a known detection circuit that converts the stem displacement of the control valve 3 into an electrical signal of 1 to 3 cm, and the detection signal is also converted into a digital signal by the A/D converter 18. It is converted and input to the arithmetic processing section 13.

The arithmetic processing unit 13 is composed of a microprocessor (CPU). This calculates the deviation between the digital signal supplied via the A/D converter 18, that is, the target value signal from the input signal detection section 11 and the valve lift signal from the valve lift detection section 12, and adjusts the valve lift accordingly. Lift control signal (PWM)
It is programmed to perform arithmetic operations as a conventional positioner to generate , and to control communication operations by the communication processing section 15 . Therefore, the arithmetic processing section 13 outputs the above-mentioned PWM signal, a pulse signal Tx for digital communication, and a switching signal Sx for switching the state of the internal switch as signals to the communication processing section 15. The communication processing unit 15 receives a received signal Rx by digital communication.
is manually input to the arithmetic processing section 13.

The electro-pneumatic conversion unit 14 is configured with a known conversion circuit that converts the valve lift control signal output as a digital signal from the arithmetic processing unit 13 into a pneumatic pressure signal.

As shown in FIG. 3, the communication processing section 15 has a pair of communication terminals 16 and 17, and performs necessary communication operations by connecting a communication device to be described later between them.

The communication processing unit 15 includes a switch S that receives either the PWM signal or the pulse signal Tx sent from the arithmetic processing unit 13, a switch S2 that is turned on or off depending on the input signal, and a switch S2 that performs arithmetic processing. Switching signal S from section 13
and a switch S3 which is turned on or off by x. The switching signal Sx turns off the switch S3 when setting the switch Sl to the input side of the pulse signal Tx, and turns on the switch S3 when setting the switch S1 to the input side of the PWM signal.

The communication processing section 15 is composed of a circuit shown in FIG. 3, and this circuit is divided into a transmitting circuit section, a receiving circuit section, and a power supply circuit section.

The oscillation circuit section connects the above-mentioned switches S2 and S3 in series via a resistor r2, connects a smoothing capacitor C1 to the switch S1, connects resistors r and r3 in parallel with these, and has both resistors r l + r 3 connection point and resistance r2+
The input circuit formed by connecting the connection point of the switch S3 and the + side (non-inverting) input terminal are connected between the resistors r and r3, and the one side (inverting) input terminal is connected to the reference potential (earth).
The circuit includes an operational amplifier AI, a transistor Q1 having a pace connected to its output terminal, and a resistor r4 connected to its emitter terminal (reference potential).

In addition to the above transistor Q1 and resistor r, the receiving circuit section includes an operational amplifier A2 whose input terminal is connected to the collector of the transistor Q1 via a coupling capacitor C2, and a diode D and resistor r5 connected to the same input terminal. , includes resistors r6 and rf connected to the + side input terminal of operational amplifier A2, and connects the output of operational amplifier A2 to the received signal Rx.
The signal is connected to be supplied to the arithmetic processing unit 13 as a signal.

Furthermore, the power supply circuit section includes the two operational amplifiers A1 and A.
a first power supply stabilizing circuit VR that creates a power supply voltage Vp (for example, 5 volts) to be supplied to each operational amplifier AI,
Voltage dividing resistors r1 and r3 connected to the + side input terminal of A2.
A second power supply stabilizing circuit VR2 generates a constant voltage Vr (for example, 25 ports) to be applied to re and r7.

Thus, the communication processing unit 15 connects the collector terminal of the transistor Q1 and one end of the resistor r4 connected to its emitter to the communication terminals 16 and 17, respectively, and the communication device 20 is connected between both terminals.

The communication device 20 is a communication interface called 5FC (smart field communicator) that performs digital communication with the communication processing unit 15, and is configured as shown in the fourth section.

That is, the communication device 20 includes a CPU 21, a keyboard 22, a display 23, a transmitting/receiving circuit 24 connected to the CPU 21, a switch 25 that is turned on/off by a switching signal from the transmitting/receiving circuit 24, and a switch 25 connected in series. Current source 26, transmitting/receiving circuit 24, and current source 26
In use, the terminal 28 on the current g26 side and the terminal 29 of the switch 250Il+ are connected to the transmission line 8, respectively.

Next, the operation of the embodiment shown in FIG. 2 will be explained.

First, when the communication terminals 16 and 17 are in an open state, that is, when the line 8 and the communication device 20 are not connected to these communication terminals, the communication processing section 15 does not operate and does not consume power. In this case, a maximum power current of 4 mA is supplied to the positioner 10 from the controller 2 through the 4-20 mA two-wire transmission lines 6 and 7 along with a 0-16 mA signal. Thereby, the positioner 10 can perform the same positioning function as the conventional one.

On the other hand, the line 8 is connected to the communication terminals 16 and 17, the line resistance R and the power supply Vp are added, and the communication device 20
By connecting, power is supplied to the communication processing unit 15, and the following communication operations can be performed.

First, when the switch Sl is set to the PWM signal input side by the switching signal Sx from the arithmetic processing section 13, the switch S3 is turned on, and the switch S2 is turned on in response to the PWM signal output from the arithmetic processing section 13. It turns on or off. As a result, the output of operational amplifier A changes, and the state of transistor Q1 changes, causing a voltage change between communication terminals 16 and 17. At this time, the transmitting/receiving circuit 24 of the communication device 20 turns off the switch 25. Therefore, the above voltage change is caused by the communication device 2 connected to the lines 6 and 7.
0 appears as a voltage change between the terminals 28 and 29, and the CPU 21 of the communication device 20 detects this via the transmitting/receiving circuit 24. This allows the communication processing unit 15 to
Communication will take place.

Next, when the switch S1 is set to the input side of the pulse signal Tx by the switching signal Sx from the arithmetic processing section 15, the switch S3 is in an OFF state, and the switch S2 is set to the input side of the pulse signal Tx output from the arithmetic processing section 13. It turns on or off depending on the situation. As a result, the output of operational amplifier A changes, the state of transistor Q1 changes, and communication terminal 16.1 changes.
7 to cause a voltage change. This voltage change is caused by the line 8
The signal is applied as a digital signal between the terminals 28 and 29 of the communication device 20 via the communication device 2o, and the CPU 21 of the communication device 2o detects this via the transmission/reception circuit 24.

As a result, the communication processing unit 15 also performs digital communication to the communication device 20.

On the other hand, when the CPU 2 i of the communication device 20 turns on/off the switch 25 via the transmitting/receiving circuit 24 and changes the current from the current source 26 between the terminals 28 and 29 in a pulsed manner, the terminal of the communication processing section 15 A voltage change between 16 and 17 occurs, and the DC component is removed by capacitor C2 and applied to one side input terminal of operational amplifier A2. Accordingly, the output of the operational amplifier A2 changes and is input to the arithmetic processing section 13 as the received signal Rx. Thus, positioner 1
A reception operation is performed.

As described above, the positioner 1o of the embodiment includes the communication device 2
By using 0, bidirectional communication can be performed, and the digital signal during communication is sent superimposed on the analog signal. Further, when not communicating, the communication processing section 15 does not consume power, so it can function as a positioner as in the conventional case.

[Effects of the Invention] Since the field device of the present invention is configured as described above, when an abnormality such as no input signal to the receiving section occurs, the receiving section receives the lowest operating energy from the transmitting section. obtained,
Actuators such as control valves can be caused to perform fail-safe operations.

Thereby, the fail-safe function of the actuator can be easily and arbitrarily realized.

[Brief explanation of the drawing]

1 is a block diagram showing the configuration of the field device of the present invention; FIG. 2 is a block diagram showing the configuration of the positioner of the embodiment; FIG. 3 is a block diagram showing the configuration of the communication processing section in FIG. 2; FIG. 4 is a block diagram showing the configuration of a communication device used in the positioner of FIG. 2. 1...Field device, 2...Controller, 3
- Control valve, 4... Receiving section, 5... Transmitting section, 6, 7.8.9... Track. Figure 1■

Claims (1)

[Claims] (1) comprising a receiving section that receives a set value signal transmitted from a controller and performs a predetermined operation corresponding to the set value, and a transmitting section that is connected to a power source and transmits the operating state of the receiving section; A field device characterized in that when a set value signal to be inputted to the receiving section is not input, the receiving section is operated in a fail-safe manner by the power supplied from the transmitting section.