JP2016156392A - Positioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a malfunction caused by lightning surge, to eliminate the need of maintenance and to automatically recover an original state.SOLUTION: A positioner 201 comprises: a surge protection circuit 7 for protecting an internal circuit of the positioner by causing a surge current that attempts to enter the internal circuit via a pair of signal lines L (L1 and L2) to flow to a ground line GND; and a surge protection circuit operation detection part 8 for detecting that the surge protection circuit 7 protects the internal circuit of the positioner 201 from the surge current. If the surge protection circuit operation detection part 8 detects operation of the surge protection circuit 7, a control part 1 (1A) keeps a current signal to an electropneumatic conversion part in a previous state. Thus, a control valve maintains an aperture at that time and the malfunction caused by lightning surge is prevented. After the lapse of a predetermined time, the state where the current signal to the electropneumatic conversion part is kept in the previous state is cancelled.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positioner that controls the opening of a control valve in accordance with the value of a control signal sent from a host device.

  Conventionally, this type of positioner is designed to operate with a 4 to 20 mA direct current signal (control signal) sent from a host device via a pair of signal lines. For example, when a current of 4 mA is sent from the host system, the opening of the control valve is 0%, and when a current of 20 mA is sent, the opening of the control valve is 100%.

  In some industrial process control systems in which such control valves are installed, for example, processing systems such as oil and gas, emergency response is important. That is, it is important that potentially toxic or flammable chemicals, gases, etc. are not leaked or discharged without control.

  For this purpose, the control valve is required to have a function of urgently shutting down (shutting down) the control valve in an emergency. Therefore, the positioner for controlling the opening degree of the control valve is designed to have the emergency cutoff function.

  For example, in the positioner shown in Patent Document 1, the value of the control signal sent from the host device is checked, and when the value of the control signal deviates from the normal range (5 to 19 mA), emergency shutdown is performed from the normal mode. The mode is switched, the current signal to the electropneumatic converter is set to zero, and the control valve is forcibly closed.

JP 2013-88917 A

  However, in a positioner having such an emergency cutoff function, for example, when the value of the control signal is equal to or lower than the lower limit threshold of the normal range and the emergency cutoff mode is set, when a lightning surge is superimposed on a pair of signal lines, The current flowing in the signal line increases due to a lightning surge, and an increase in the value of the control signal due to this increase in current is mistakenly recognized as entering the normal range, and the control valve may be opened and closed in the normal mode.

  Although it is conceivable that a surge current that attempts to enter the internal circuit of the positioner through a pair of signal lines is interrupted by a fuse, the influence of the lightning surge can be stopped, but the original state cannot be automatically restored. Also, maintenance such as fuse replacement is required.

  The present invention has been made in order to solve such problems. The object of the present invention is to prevent a malfunction due to a lightning surge, to eliminate the need for maintenance, and to automatically return to the original state. To provide a positioner.

  In order to achieve such an object, the present invention inputs a control signal sent from a host device through a pair of signal lines and a valve opening signal fed back from a control valve, and a value indicated by the control signal. And a value indicating the valve opening signal, a controller that outputs a current signal according to the deviation, and an electropneumatic converter that converts the current signal from the controller into a pneumatic signal. Surge protection that protects the internal circuit of the positioner by flowing a surge current that tries to enter through a pair of signal lines to the ground line in a positioner that supplies output air pressure to the control valve actuator based on the air pressure signal from the converter A circuit and a surge protection circuit operation detection unit that monitors the operation of the surge protection circuit and detects that the surge protection circuit has protected the internal circuit of the positioner from surge current. The control unit is characterized in that the current signal to the electro-pneumatic conversion unit is kept in the previous state when the surge protection circuit operation detection unit detects the protection of the internal circuit of the positioner from the surge current by the surge protection circuit. To do.

  In the present invention, the surge protection circuit protects the internal circuit of the positioner from the surge current by causing a surge current to enter through the pair of signal lines to flow through the ground line. The operation of the surge protection circuit is monitored by a surge protection circuit operation detector. When the operation of the surge protection circuit is detected by the surge protection circuit operation detection unit, that is, when it is detected that the surge protection circuit protects the internal circuit of the positioner from the surge current, the control unit is connected to the electropneumatic conversion unit. Keep the current signal in the previous state.

  As a result, for example, when the control valve is fully closed in the emergency shut-off mode, if a surge current tries to enter through the pair of signal lines, this surge current flows to the ground line and the internal circuit of the positioner is protected. At the same time, the control valve remains fully closed as the previous state. This prevents malfunctions due to lightning surges. In addition, since the inside of the positioner is protected by flowing a surge current through the ground line, maintenance such as replacement of a fuse is unnecessary.

  Moreover, in this invention, when the surge protection circuit operation | movement detection part detects the action | operation of a surge protection circuit, the electric current signal to an electropneumatic conversion part is maintained in the last state. Since the surge current flows instantaneously, if the state where the current signal to the electropneumatic converter is kept in the previous state is released after a predetermined time, the current signal is output to the electropneumatic converter. Is resumed, and the original state is automatically restored.

  According to the present invention, a surge protection circuit that protects the internal circuit of the positioner by flowing a surge current that tries to enter through a pair of signal lines to the ground line, and the surge protection circuit protects the internal circuit of the positioner from the surge current. Since the surge protection circuit operation detection unit detects the operation of the surge protection circuit when the surge protection circuit operation detection unit detects the operation of the surge protection circuit, the current signal to the electropneumatic conversion unit is kept in the previous state. In addition to preventing malfunctions caused by lightning surges, maintenance is not required and automatic return to the original state is possible.

It is a figure which shows the structure of the principal part of one Embodiment of the positioner which concerns on this invention. It is a figure which shows the basic composition of the conventional positioner.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, prior to describing the embodiment of the positioner according to the present invention, the basic configuration of a conventional positioner will be described.

[Conventional positioner]
FIG. 2 is a view showing a main part of a conventional positioner. In the figure, 100 is a host device, 200 is a positioner, and 300 is a control valve. The positioner 200 includes a control unit 1, an electropneumatic conversion unit 2, a pilot relay 3, an opening degree sensor 4, and a comparison circuit 5.

  In this positioner 200, the control unit 1 includes a control signal (DC current signal) of 4 to 20 mA sent from the host device 100 through a pair of signal lines L (L1, L2), and an opening sensor from the control valve 300. 4 is used as an input to obtain the deviation between the value indicated by the control signal (set opening θsp) and the value indicated by the valve opening signal (actual opening θpv). A current signal Io corresponding to

  The electropneumatic converter 2 receives the current signal Io from the controller 1 and converts the input current signal Io into an air pressure signal Pn. The pilot relay 3 amplifies the air pressure signal Pn from the electropneumatic converter 2 and supplies it to the operating device 6 of the control valve 300 as the output air pressure Pout.

  The comparison circuit 5 takes a control signal from the host device 100 to the control unit 1 as a branch input, compares the value of this branch-input control signal with a normal range defined for the control signal, The comparison result is output to the control unit 1.

  In this example, the normal range of the control signal in the comparison circuit 5 is determined as 5 to 19 mA. That is, for the comparison circuit 5, 5 mA is set as the lower limit threshold, and 19 mA is set as the upper limit threshold.

  When the comparison result that the value of the control signal deviates from the normal range is sent from the comparison circuit 5, the control unit 1 indicates the value (set opening θsp) indicated by the control signal and the valve opening signal. Regardless of the deviation from the value (actual opening θpv), the current signal Io to the electropneumatic converter 2 is forcibly adjusted to zero. As a result, the output air pressure Pout from the positioner 200 is substantially reduced to near zero, and the control valve 300 is forcibly fully closed.

  In this positioner 200, the value of the control signal sent from the host device 100 through the pair of signal lines L (L1, L2) is checked, and when the value of this control signal deviates from the normal range (5 to 19 mA), The normal mode is switched to the emergency cutoff mode, the current signal Io to the electropneumatic converter 2 is set to zero, and the control valve 300 is forcibly fully closed. In this example, the control valve 300 is forcibly fully closed in the emergency cutoff mode, but there is a type in which the control valve 300 is forcibly fully opened.

Embodiment
In the present embodiment, a surge protection circuit 7 and a surge protection circuit operation detection unit 8 are provided with respect to the conventional positioner 200 shown in FIG. 2, as shown in FIG. The positioner of this embodiment provided with the surge protection circuit 7 and the surge protection circuit operation detection unit 8 is referred to as a positioner 201.

  In the present embodiment, the surge protection circuit 7 includes a first surge voltage absorbing element (Zener diode) ZD1 connected between one L1 of the pair of signal lines L and the ground line GND, and the pair of signal lines L. And a second surge voltage absorbing element (Zener diode) ZD2 connected between the other L2 of the second and the ground line GND, and a surge current to enter through a pair of signal lines L (L1, L2) The internal circuit of the positioner 201 is protected by flowing to GND.

  That is, when a surge current tries to enter from one L1 of the pair of signal lines L, the surge current flows to the ground line GND through the first surge voltage absorbing element ZD1, and from the other L2 of the pair of signal lines L When a current is about to enter, a surge current is passed through the ground line GND through the second surge voltage absorbing element ZD2, and the internal circuit of the positioner 201 is protected from the surge current about to enter. In this case, since a surge current is caused to flow to the ground line GND through the surge voltage absorbing elements ZD1, ZD2, maintenance such as replacement of a fuse is unnecessary.

  In this embodiment, the surge voltage absorbing elements ZD1 and ZD2 are Zener diodes, but a varistor or the like may be used. Further, the surge voltage absorbing elements ZD1 and ZD2 may be provided not on the inside of the positioner 201 but on the outside.

  In the present embodiment, the surge protection circuit operation detection unit 8 includes a comparator 8-1, a reference voltage generation circuit (reference IC) 8-2, a capacitor C1, and a resistor R1, and the comparator 8- The reference voltage (threshold voltage) Vth from the reference voltage generation circuit 8-2 is given to the non-inverting input terminal (+) of 1, and the capacitor C1 and the resistor R1 are connected in series to the inverting input terminal (−) of the comparator 8-1. A potential at a connection point P1 between the surge voltage absorbing elements ZD1 and ZD2 and the ground line GND, that is, a connection point P1 between the anodes of the Zener diodes ZD1 and ZD2 and the ground line GND is given through the circuit.

  In the surge protection circuit operation detection unit 8, the comparator 8-1 compares the potential of the connection point P1 input to the inverting input terminal (−) with the threshold voltage Vth input to the non-inverting input terminal (+), The comparison result is transmitted to the control unit 1. That is, the operation of the surge protection circuit 7 is monitored, and when the surge current flows to the ground line GND through the surge voltage absorbing elements ZD1, ZD2, and the potential at the connection point P1 exceeds the threshold voltage Vth, the surge protection circuit 7 is activated. Is notified to the control unit 1.

  In the present embodiment, when the control unit 1 receives notification from the surge protection circuit operation detection unit 8 that the surge protection circuit 7 has been activated, that is, the surge protection circuit operation detection unit 8 detects from the surge current generated by the surge protection circuit 7. When the notification that the protection of the internal circuit of the positioner 201 is detected is received, the current signal Io to the electropneumatic converter 2 has a function of maintaining the previous state. Further, the control unit 1 has a function of canceling a state in which the current signal Io to the electropneumatic conversion unit 2 is maintained in a previous state after a predetermined time has elapsed.

  In order to distinguish the control unit 1 in the positioner 201 of the present embodiment from the control unit 1 in the conventional positioner 200 shown in FIG. The control unit 1 in the conventional positioner 200 shown in FIG. The control unit 1A is realized by hardware including a processor and a storage device, and a program that realizes various functions in cooperation with the hardware.

  In the positioner 201 of the present embodiment, malfunction due to lightning surge is prevented by the above-described function of the control unit 1A. In addition, after avoiding malfunction due to lightning surge, it automatically returns to the original state immediately.

  That is, in the conventional positioner 200, for example, when the value of the control signal is equal to or lower than the lower limit threshold value (5 mA) of the normal range and the emergency cutoff mode is set, the lightning surge seems to be superimposed on the pair of signal lines L (L1, L2). In this case, the current flowing through the pair of signal lines L (L1, L2) increases due to lightning surge, and the increase in the value of the control signal due to the increase in current is erroneously recognized as having entered the normal range. There is a possibility that the control valve 300 is opened and closed in the mode.

  On the other hand, in the positioner 201 of the present embodiment, when a lightning surge is superimposed in the emergency cut-off mode, a surge current flows to the ground line GND through the surge voltage absorbing elements ZD1 and ZD2, and the internal positioner 201 The circuit is protected. At the same time, the surge protection circuit operation detection unit 8 detects the operation of the surge protection circuit 7 and notifies the control unit 1 so that the control unit 1 sets the current signal Io to the electropneumatic conversion unit 2 to the previous state. keep. As a result, the state in which the control valve 300 is fully closed is maintained, and malfunction due to lightning surge is prevented.

  Further, after maintaining the current signal Io to the electropneumatic converter 2 in the immediately preceding state, the control unit 1 cancels the state in which the current signal Io is maintained in the immediately preceding state when a predetermined time has elapsed. As a result, the output of the current signal Io to the electropneumatic converter 2 is resumed, and the original state is automatically restored. If the control signal enters the normal range due to this automatic return to the original state, the transition from the emergency cutoff mode to the normal mode is performed, and if the control signal deviates from the normal range, the normal mode switches to the emergency cutoff mode. Transition takes place.

  In the above-described example, the case where the lightning surge is superimposed when the emergency cut-off mode is set has been described. However, when the lightning surge is superimposed when the normal mode is set, the surge is similarly applied. The protection circuit 7 is activated and the internal circuit of the positioner 201 is protected, and the surge protection circuit operation detection unit 8 detects the operation of the surge protection circuit 7 and notifies the control unit 1 of the current to the electropneumatic conversion unit 2 The signal Io is kept in the previous state. Thereby, the opening degree of the control valve 300 maintains the opening degree at that time, and malfunction due to lightning surge is prevented. In addition, when the predetermined time has elapsed, the opening / closing operation in the normal mode is resumed.

[Extension of the embodiment]
The present invention has been described above with reference to the embodiment. However, the present invention is not limited to the above embodiment. Various changes 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 technical idea of the present invention.

  DESCRIPTION OF SYMBOLS 1 (1A) ... Control part, 2 ... Electropneumatic conversion part, 3 ... Pilot relay, 4 ... Opening sensor, 5 ... Comparison circuit, 6 ... Operation device, 7 ... Surge protection circuit, 8 ... Surge protection circuit operation detection part , ZD1, ZD2 ... surge voltage absorbing element (Zener diode), 8-1 ... comparator, 8-2 ... reference voltage generation circuit (reference IC), C1 ... capacitor, R1 ... resistor, L (L1, L2) ... pair Signal line 100 ... host device 201 ... positioner 300 ... control valve

Claims (3)

The control signal sent from the host device through a pair of signal lines and the valve opening signal fed back from the control valve are input, and the difference between the value indicated by the control signal and the value indicated by the valve opening signal And a control unit that outputs a current signal according to the deviation and an electropneumatic conversion unit that converts the current signal from the control unit into a pneumatic signal, and based on the pneumatic signal from the electropneumatic conversion unit In a positioner for supplying output air pressure to the control valve actuator,
A surge protection circuit that protects the internal circuit of the positioner by flowing a surge current that attempts to penetrate through the pair of signal lines to the ground line;
A surge protection circuit operation detection unit that monitors the operation of the surge protection circuit and detects that the surge protection circuit protects the internal circuit of the positioner from the surge current;
The controller is
When the surge protection circuit operation detection unit detects the protection of the internal circuit of the positioner from the surge current by the surge protection circuit, the current signal to the electropneumatic conversion unit is maintained in a previous state. Positioner. The positioner as claimed in claim 1,
The controller is
A positioner that releases a state in which a current signal to the electropneumatic converter is kept in a previous state after a lapse of a predetermined time. The positioner according to claim 1 or 2,
The surge protection circuit is
A first surge voltage absorbing element connected between one of the pair of signal lines and the ground line; and a second surge voltage connected between the other of the pair of signal lines and the ground line. A surge current flowing through the ground line through at least one of the first and second surge voltage absorption elements.
The surge protection circuit operation detection unit is
As the operation of the surge protection circuit, the potential of the connection point between the first and second surge voltage absorbing elements and the ground line is monitored, and when the potential exceeds a predetermined threshold, the surge protection circuit A positioner that detects that the internal circuit of the positioner is protected from the surge current.

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