JP2003287003A - Valve positioner - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable a fail-safe operation to be easily realized in a valve positioner. SOLUTION: A valve opening target value signal SP is input, and a valve is set based on a deviation between the valve opening target value signal SP and a stem displacement signal PV obtained by converting the valve opening of the valve into an electric signal. A control means for generating an operation signal MV for controlling the opening position, an air flow rate in which the supply pressure Ps is reduced by a fixed throttle, is supplied to the nozzle, and an air flow rate ejected from the nozzle is blocked by a flapper, whereby the nozzle is closed. A nozzle / flapper mechanism for varying the back pressure Pn; electropneumatic conversion means for controlling the nozzle back pressure Pn by changing the position of the flapper of the nozzle / flapper mechanism in accordance with the operation signal MV; In a valve positioner having a pilot relay mechanism for outputting an output air pressure Po corresponding to Pn to a control valve, the output is controlled by controlling the nozzle back pressure Pn to a maximum or a minimum. A valve positioner provided with fail-safe means for controlling the air pressure Po to a maximum or a minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve positioner, and more particularly, it can easily perform a fail-safe operation in an electropneumatic valve positioner that controls a valve opening position of a valve that is a control valve used in a process plant. The valve positioner.

[0002]

2. Description of the Related Art A conventional valve positioner is shown in FIG.
As shown in FIG. 3, the valve opening target signal SP and the supply pressure Ps are given from the outside, and the valve opening signal PV (not shown) of the valve 18 is transmitted through the link mechanism L to an angle sensor or the like in the valve positioner 10. In this configuration, the output pressure Po is controlled so that the valve opening signal (PV) corresponding to the valve opening target value signal SP matches.

Such a valve positioner 10 is constructed so that the air pressure reduced by the air pressure regulator 26 is input as a rated air pressure, and the air pressure is adjusted by an electric signal to control the link mechanism L to control the valve 18.

The valve positioner 10 having such a mechanism, as shown in FIG. 7, includes a first signal converter 11 for inputting a valve opening target value signal SP and converting it into a signal which can be internally calculated, and a valve. The opening degree target value signal SP and the stem displacement signal PV representing the valve opening degree from the valve 18 are compared, and a comparator 12 which outputs a deviation signal thereof and a valve opening degree target value signal SP by inputting the deviation signal And the stem displacement signal PV are matched with each other, a control device 13 for calculating an operation signal MV, a second signal converter 14 for inputting the operation signal MV and converting it into an electric signal Ic, and an electric signal Ic are inputted. Pneumatic signal Pn
Electro-pneumatic converter 15 that adopts a nozzle / flapper system that converts the output pressure signal Po, a pilot relay 16 that controls the output pressure signal Po by the air pressure signal Pn, and a stem 3 of the valve 18.
The position sensor 19 for detecting the displacement Yp of 1 and the stem displacement signal PV by converting the signal obtained by the position sensor 19
And a third signal converter 20 which outputs

Further, the control valve 30 is a valve positioner 1
The drive unit 17 generates a force according to the output pressure Po output from 0, the stem 31 that transmits the force generated by the drive unit 17 to the valve 18, and the valve 18 that is interlocked with the stem 31.

Here, the valve positioner 10 supplies the output pressure Po to the drive portion 17 of the control valve 30 and detects the position signal Yp of the stem 31 to sense the valve opening degree of the valve 18 and control loop. Is closed.

In the valve positioner 10 having such a configuration, first, the valve opening target value signal SP is given and converted by the first signal converter 11 into a signal that can be internally calculated. When the valve opening target value signal SP is a current signal such as 4-20 mA, the first signal converter 11 converts it into a voltage signal that is input to the operational amplifier. When the valve opening target value signal SP is a digital signal, the communication signal is converted into a digital signal. The valve opening target value signal SP converted into a signal that can be recognized by this device is compared with the stem displacement signal PV from the control valve 30, and the deviation signal thereof is input to the control device 13. The controller 13 calculates the deviation,
An operation signal MV that matches the valve opening target value signal SP and the stem displacement signal PV is calculated and obtained. At this time, the part that calculates the deviation between the valve opening target value signal SP and the valve opening signal PV may also be regarded as the control device 13.

The calculated operation signal MV is input to the second signal converter 14 and then to the electropneumatic converter 15. When the drive signal of the electro-pneumatic converter 15 and the operation signal MV are different,
The second signal converter 14 performs signal conversion. For example, the drive signal of the electropneumatic converter 15 is a current signal, and the operation signal MV
Is a voltage signal, the second signal converter 14
(Voltage / current) converter, etc., and a current signal (electrical signal I
c). The electropneumatic converter 15 converts the electric signal Ic into the air signal Pn. In many cases, this mechanism generally employs a nozzle / flapper system. The electric signal Ic converted into the air signal Pn by the electropneumatic converter 15 is converted into the output pressure Po by the pilot relay 16 which is a pressure amplifier. The pressure Po output from the valve positioner 10 is input to the drive unit 17 of the control valve 30, and the valve opening signal Yp corresponding to the pressure is generated. Valve opening signal Yp of the control valve 30
Is sensed by the position sensor 19 and input to the third signal converter 20.

In the third signal converter 20, the valve opening signal Y
Convert p into a signal that the device can recognize. Position sensor 1
The output signal of 9 varies depending on the form of the sensor, but a voltage signal output is general. In this case, the output signal of the position sensor 19 is assumed to be a voltage signal. In the case of an analog device, the third signal converter 20 generally has a function of amplifying the voltage signal received from the position sensor 19. In the case of digital equipment, position sensor 1
The voltage signal received from 9 is converted into a digital value by an AD converter or the like. Stem displacement signal PV thus obtained
Is compared with the valve opening target value signal SP, and the control device 1
3 forms a negative feedback loop in which the deviation is input. With such a control loop configuration, the valve positioner 10
Controls the valve opening of the valve 18.

In this way, the valve positioner 10 is provided with the valve opening target value signal SP and the supply air pressure from the outside, and controls the control valve 30 so that the valve opening degree is adjusted according to the valve opening target value signal SP. Control. In this case, the valve opening target value signal S
P is, for example, an analog signal of 4 to 20 mA, and is, for example, a foundation field bus (Founda).
digital communication protocol typified by a digital camera (Field Fieldbus). The supply air pressure is normally supplied to the valve positioner 10 as a rated air pressure for the control valve 30 by reducing the factory pressure with an air pressure regulator.

When the valve positioner 10 equipped with the electro-pneumatic converter 15 having the above-described structure and operation falls into an abnormal state, a service person calls on the site to perform a fail-safe operation. The following methods can be considered as fail-safe operation methods. A fail safe signal is provided to the valve positioner 10. Fail-safe operation is realized by turning off the power. A fail-safe operation is realized by reducing the air pressure.

[0012]

However, when an abnormal state occurs in the valve positioner as described above,
The structure is such that fail-safe operation of ~ cannot be easily realized.

Specifically, regarding the analog signal positioner of 4 to 20 mA and the digital communication type positioner, in order to change the signal to be applied to the valve positioner, a device (signal conditioner) for applying a signal to the valve positioner is used. Alternatively, it is necessary to operate a higher-level control system (DCS system, etc.), which cannot be immediately performed at the site where the valve is actually installed.

Regarding the above, although the current supplied to the valve positioner can be reduced by removing the wiring of the valve positioner, it is not easy to remove the wiring terminal because of the design of the field device. Alternatively, in the case of a valve positioner that is performing digital communication, in most cases, the signal bus line is shared with other equipment by multi-drop, and removing the wiring of the valve positioner is all that is connected to the bus. It is not realistic because it will disconnect the signal line of the device.

As for the above, the air pressure regulator for reducing the factory pressure is not always near the valve. In addition, a plurality of valve positioners may be operated by one air pressure regulator, and it may not be possible to easily reduce the air pressure.

For the above reasons, there is a problem that it is extremely difficult to perform the fail-safe operation even when the user goes to the installation location of the valve where the problem occurs.

In rare cases, the direction in which the power is turned off or the direction in which the air pressure is dropped is not the fail-safe operation. In such a case, means for realizing the fail-safe operation other than operating the signal given to the valve positioner. There is also a problem that there is no.

The present invention solves such a problem, and an object thereof is to make it possible to easily realize a fail-safe operation in a valve positioner.

[0019]

A valve positioner of the present invention that achieves the above object is as follows. (1) The valve opening target value signal SP is input, and the valve is opened based on the deviation between the valve opening target value signal SP and the stem displacement signal PV obtained by converting the valve opening of the valve into an electric signal. The control means for generating the operation signal MV for controlling the degree position, and the air flow rate obtained by squeezing the supply pressure Ps with a fixed throttle are supplied to the nozzle,
By blocking the flow rate of air ejected from the nozzle with a flapper, by changing the nozzle / flapper mechanism that changes the back pressure Pn of the nozzle and the position of the flapper of the nozzle / flapper mechanism according to the operation signal MV. In a valve positioner equipped with an electropneumatic conversion means for controlling the nozzle back pressure Pn and a pilot relay mechanism for outputting an output air pressure Po corresponding to the nozzle back pressure Pn to a control valve, the nozzle back pressure Pn is maximized or minimized. A valve positioner provided with fail-safe means for controlling the output air pressure Po to a maximum or a minimum by controlling the output air pressure Po. (2) The valve positioner according to claim 1, wherein the fail-safe means directly mechanically operates the nozzle back pressure generated by the nozzle / flapper mechanism to a minimum pressure or a maximum pressure. (3) The fail-safe means is configured to operate the nozzle back pressure to a minimum pressure or a maximum pressure by maximizing or minimizing the electric signal Ic input to the electropneumatic converting means. The valve positioner according to claim 1. (4) The fail-safe means includes an indicator indicating a fail-safe direction.
Valve positioner described in. (5) The valve positioner according to claim 1, wherein the fail-safe means includes a protect means for preventing an operation direction opposite to the fail-safe direction.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a valve positioner according to the present invention will be described with reference to the drawings. still,
The same components as those described in the related art will be described with the same reference numerals.

As shown in FIG. 1, the valve positioner according to the present invention has fail safe mechanism portions 21a and 21b for controlling the valve 18 to be fully closed or fully opened, and the valve opening target value signal SP The first signal converter 11 for inputting and converting into a signal which can be internally calculated is compared with the valve opening target value signal SP and the stem displacement signal PV representing the valve opening from the control valve 30, and the deviation signal thereof is compared. Comparator 12 for outputting
And a control device 13 that inputs the deviation signal to calculate an operation signal MV that matches the valve opening target value signal SP and the stem displacement signal PV, and the operation signal MV that is input and converted into an electric signal Ic. Second signal converter 14 and operation signal M
A fail-safe mechanism (electrical type) 21a that operates the electric signal Ic to the maximum or minimum regardless of the value of V, and an electro-pneumatic converter 15 that adopts a nozzle / flapper system that converts the electric signal Ic into an air signal Pn. A fail-safe mechanism section 21b (mechanical type) that operates the air signal Pn to the maximum or minimum regardless of the value of the electric signal Ic, and the output pressure Po of the control valve 30 by controlling the output pressure Po by the air signal Pn. The pilot relay 16 supplied to the drive unit 17, the position sensor 19 that detects the valve opening signal Yp, and the third signal converter 20 that converts the signal obtained by the position sensor 19 and outputs the stem displacement signal PV. Consists of.

As described above, according to the present invention, the fail-safe mechanism portion 21 is added to the valve positioner 10 described in the prior art.
a, 21b is provided, and the fail-safe mechanism portions 21a, 21b are in the fail-safe state,
Whether the valve 18 should be fully closed or fully open depends on the process design of the plant. Also,
When the output pressure Po is atmospheric pressure, whether the valve 18 is fully closed or fully opened depends on the design of the control valve 30. Therefore, the valve positioner 10 must be able to perform a binary operation from the outside to reduce the output pressure Po to the atmospheric pressure or increase it to the supply pressure Ps.

The fail-safe mechanism portion 21 performs such an operation. The fail-safe mechanism unit 21a has a structure that directly operates the electric signal Ic from the outside of the device, and the fail-safe mechanism unit 21b has a structure that operates the air signal Pn.

Since the output pressure Po of the valve positioner 10 is a signal determined by the electric signal Ic or the air signal Pn, it is necessary to operate the electric signal Ic or the air signal Pn from the outside in the fail-safe mechanism parts 21a and 21b. Thus, the output pressure Po can be operated in the direction desired by the user.

Hereinafter, the fail-safe mechanism portion 21a and the air signal P by electric means for externally operating the electric signal Ic.
Two fail-safe mechanism parts 21b which are mechanical means for operating n externally will be described.

Fail safe mechanism section 2 by mechanical means
1b is the air signal Pn of the nozzle back pressure as shown in FIG.
The pipe passing through is formed in a cross shape, the pipe in the upper direction is arranged in the nozzle direction of the nozzle / flapper mechanism portion 25, and the pipe in the downward direction is arranged so that the nozzle back pressure Pn is supplied, and the pipe in the right direction is arranged. Is arranged so that the atmospheric pressure AIR enters, and the piping on the left side is arranged so that the supply pressure Ps enters.

The example of FIG. 2 has a structure in which the electro-pneumatic converter 15 includes a fail-safe mechanism section 21a inside.

A first valve 22 is provided in the pipe arranged in the nozzle direction, and a second valve is provided in the pipe for drawing in the atmospheric pressure AIR.
The valve 23 is provided, and the fixed throttle 24 is provided in the pipe for drawing in the supply pressure Ps.

The fail-safe mechanism section 21b having such a structure can perform fail-safe operation by mechanical means. That is, the air signal Pn of the nozzle back pressure of the nozzle / flapper mechanism unit 25 that receives the electric signal Ic from the second signal converter 14 side is set to the maximum pressure or the minimum pressure regardless of the flapper position, that is, the value of the electric signal Ic. The pressure is controlled to control the output pressure of the valve positioner 10. Here, the minimum pressure of the air signal Pn of the nozzle back pressure is the same as the atmospheric pressure, and the maximum pressure is the same as the supply pressure Ps. Nozzle back pressure Pn minimum value = atmospheric pressure AIR Nozzle back pressure Pn maximum value = supply pressure Ps

Therefore, in order to make the air signal Pn of the nozzle back pressure the maximum pressure or the minimum pressure, the first and second valves 2
It suffices to open and close 2, 23 to control.

Specifically, as shown in FIG. 3, when the nozzle back pressure Pn is the atmospheric pressure AIR, the first valve 22 is turned on.
Either pen or Close, second valve 2
When 3 is Open, the atmospheric pressure AIR becomes the nozzle back pressure.

When the nozzle back pressure Pn is the supply pressure Ps, the first valve 22 is Close and the second valve 23 is Cl.
If it is ose, the transmission of the supply pressure Ps to the nozzle is blocked, and the atmospheric pressure AIR is also shielded.
All of s becomes the nozzle back pressure Pn.

When the nozzle back pressure Pn is in the normal state, the first valve 22 is Open and the second valve 23 is Close.
If so, the supply pressure Ps is transmitted to the nozzle.

In this way, the first and second valves 2
It is possible to mechanically control the nozzle back pressure Pn by controlling the opening / closing of the valve Nos. 2 and 23 and thereby perform the desired fail-safe operation by controlling the air pressure, regardless of other devices. Can be done at.

Further, it goes without saying that the first and second valves 22 and 23 may be manually operated or may be remotely operated. By using the valves 22 and 23, the fail-safe operation can be realized as an external switch.

Next, the fail-safe mechanism section 21a for maximizing or minimizing the air pressure of the nozzle back pressure by electrical means is an electromagnetic circuit including the coil of the nozzle / flapper mechanism section 25 in the electropneumatic converter 15. It is a configuration for controlling.

That is, the current Ic flowing through the coil of the nozzle / flapper mechanism section 25 of the electropneumatic converter 15 is controlled to control the nozzle back pressure Pn to be atmospheric pressure, supply pressure, or atmospheric pressure.

This fail-safe mechanism portion 21a is shown in FIG.
As shown in FIG. 2, the first and second switches (SW
1, SW2) 26, 27 is provided as a circuit configuration,
By controlling ON / OFF of the second switches (SW1, SW2) 26, 27 and controlling the current flowing through the coil 30, the supply pressure, the atmospheric pressure, and the normal state are changed.

The circuit configuration of the fail-safe mechanism portion 21a is such that the switching element 29 connected in series with the coil 30 is used.
And a resistor R, an amplifier 28 for inputting a control signal MV from the controller 13 connected to the gate of the switching element 29, one side connected to the input end of the coil 30, and the other side connected to the input side of the amplifier 28. First switch (SW
1) 26 and a second switch (SW) having one side connected to the input end of the amplifier 28 and the other side connected to the other end of the resistor R.
2) 27.

In the fail-safe mechanism section 21a having such a circuit configuration, the current applied to the coil 30 is maximized / minimized by operating the control signal and the first and second switches (SW1, SW2) 26, 27. By controlling, the nozzle back pressure Pn can be changed to the supply pressure / atmospheric pressure.

More specifically, as shown in FIG. 5, in order to minimize the nozzle back pressure Pn, the first switch (S
W1) 26 is turned off, and the second switch (SW2) 27 is turned on.

In order to maximize the nozzle back pressure Pn, the first switch (SW1) 26 is turned on and the second switch (SW1) is turned on.
2) Turn off 27.

When the nozzle back pressure Pn is in the normal state, both the first and second switches (SW1, SW2) 26, 27 are turned off.

Such first and second switches (SW
1, SW2) 26 and 27 are provided, the fail-safe operation can be realized from the outside. Further, since the control signal MV may be calculated by a microcomputer or the like, the same function can be realized by interlocking a digital signal that makes the control signal MV the maximum value / minimum value with an external switch.

Further, the first and second valves 22 and 23, which are the mechanical means shown in FIG. 2, are operated to set the nozzle back pressure to the maximum pressure or the minimum pressure. When operating to the pressure opposite to the supply pressure Ps,
Although not shown, an erroneous operation prevention indicator for notifying that effect is provided. This indicator may be a simple one, such as an arrow, which indicates the direction of pressure operation, or may display the data accurately, or may display the result separately calculated by the control means such as a microcomputer.

Further, an erroneous operation may be prevented by providing an erroneous operation prevention stopper for protecting the pressure operation in the opposite direction.

First and second electrical means shown in FIG.
If a switch for fail-safe operation is provided by the switches 26 and 27, there is a risk that a switch in the opposite direction to the fail-safe may be turned on depending on how the switch is turned on. As a measure against this, an erroneous operation can be eliminated by installing an indicator indicating the direction of fail-safe operation or an erroneous operation prevention stopper.

In the case of the indicator, it can be recognized as a fail-safe button by changing the color of the button or by using an arrow or the like.

In the case of an erroneous operation stopper, the mechanism is such that a button that is not failsafe cannot be pressed mechanically.

[0050]

As described above, the valve positioner of the present invention performs the mechanical or electrical operation to maximize the nozzle back pressure obtained by the electropneumatic converter in a state independent of the operation signal PV. Alternatively, by providing fail-safe means to minimize the pressure, when an abnormality occurs in the valve positioner, fail-safe operation can be performed quickly and without affecting other devices, etc. for each valve positioner that has an abnormality. The effect is that it can be done.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram schematically showing a valve positioner of the present invention.

FIG. 2 is a block diagram of a fail-safe mechanism portion by mechanical means provided in the electro-pneumatic converter.

[FIG. 3] OPEN the first and second valves shown in FIG.
/ CLOSE is a list display of controlling the nozzle back pressure.

FIG. 4 is a block diagram of a fail-safe mechanism portion by electric means provided in the electro-pneumatic converter.

FIG. 5 is a circuit diagram showing that the first and second switches shown in FIG.
It is a list display of controlling the nozzle back pressure by turning off.

FIG. 6 is an explanatory view schematically showing a configuration relating to a nozzle / flapper mechanism section and a valve positioner.

FIG. 7 is an overall configuration diagram of a valve positioner in a conventional technique.

[Explanation of symbols]

10 valve positioner 11 First signal converter 12 Comparator 13 Control device 14 First signal converter 15 Electro-pneumatic converter 16 pilot relay 17 Drive 18 valves 19 Position sensor 20 Third signal converter 21a, 21b Fail-safe mechanism part 22 First valve 23 Second valve 24 fixed aperture 25 Nozzle / Flapper mechanism 26 First Switch (SW1) 27 Second switch (SW2) 28 amplifiers 29 switching elements 30 control valve L-link mechanism C coil

Claims (5)

[Claims] 1. A valve opening target value signal SP is input, and based on a deviation between the valve opening target value signal SP and a stem displacement signal PV obtained by converting the valve opening of the valve into an electric signal. Control means for generating an operation signal MV for controlling the valve opening position, and an air flow rate obtained by narrowing the supply pressure Ps with a fixed throttle are supplied to the nozzle, and an air flow rate ejected from the nozzle is blocked by a flapper, whereby the nozzle Nozzle for changing back pressure Pn of
Nozzle back pressure Pn by changing the flapper mechanism and the flapper position of the nozzle / flapper mechanism according to the operation signal MV.
In a valve positioner including an electro-pneumatic conversion means for controlling the nozzle back pressure Pn, and a pilot relay mechanism for outputting an output air pressure Po corresponding to the nozzle back pressure Pn to a control valve, by controlling the nozzle back pressure Pn to a maximum or a minimum. A valve positioner provided with fail-safe means for controlling the output air pressure Po to a maximum or a minimum. 2. The valve according to claim 1, wherein the fail-safe means directly mechanically operates the nozzle back pressure generated by the nozzle / flapper mechanism to a minimum pressure or a maximum pressure. Positioner. 3. The fail-safe means controls the nozzle back pressure to a minimum pressure or a maximum pressure by maximizing or minimizing an electric signal Ic input to the electro-pneumatic converting means. The valve positioner according to claim 1. 4. The valve positioner according to claim 1, wherein the fail-safe means includes an indicator that indicates a fail-safe direction. 5. The fail safe means comprises a protect means for preventing an operation direction opposite to the fail safe direction.
Alternatively, the valve positioner according to claim 4.