JPH0816249A - Positioner - Google Patents

Abstract

PURPOSE:To prevent the generation of a change in an output of a pilot relay independently of a change in peripheral temperature or the creeping of a constitutional member and the generation of zero point shifting and to make it unnecessary for a worker to adjust a zero point by forming a nozzle on a center leg part of a yoke and leading the back pressure of the nozzle into a bias room of the pilot relay. CONSTITUTION:A 1st nozzle 16 is formed on the tip face of one side leg part 31a on the outside of the yoke 31 is fixed on a base 30 so as to be opposed to the vicinity of a flapper 14 and a 2nd nozzle 60 is formed on the tip of a center leg part 31b correspondingly to a fulcrum 15 of the flapper 14. An air feeding piping 20 is connected to the 2nd nozzle 60 through a throttle 61 and the back pressure PN' of the nozzle 60 is led into the bias room 42 of the pilot relay 44. Namely, the back pressure PN' of the 2nd nozzle 60 arranged in the vicinity of the fulcrum 15 is led into the bias room 42 instead of fed air pressure Psup.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a valve positioner or the like used for controlling the operating shaft of an automatic control valve used in various plants such as petrochemical and chemical industries to a position according to an input signal. It relates to a suitable positioner.

[0002]

2. Description of the Related Art Conventionally, a positioner for an automatic control valve is mounted on a yoke of a drive unit, and mechanical displacement of a working shaft of the automatic control valve is mechanically fed back by a lever or the like so that a relationship between a meter signal and a valve shaft position can be obtained. In order to always maintain accurate against the disturbance, a kind of servo mechanism that adjusts the output air pressure to the drive unit by using the drive shaft position as the detection end, and normally converts the input signal (displacement signal) as the swing displacement of the flapper. Then
The nozzle / flapper mechanism converts this to an air pressure signal for amplification, and then supplies it as a drive pressure to a drive device for the control valve to drive and control the control valve. Further, in this type of positioner, the actual operation amount of the control valve is fed back to the flapper by a feedback mechanism so as to be balanced with the force by the input signal.

FIG. 3 shows a conventional example of such a valve positioner. Briefly explaining based on the figure,
Reference numeral 1 is an automatic control valve, 2 is an operating shaft of the automatic control valve 1, 3 is a pneumatic drive device mounted on the upper portion of the automatic control valve 1 via a yoke (not shown), and 4 is on one side of the yoke. A valve positioner screwed and fixed via a bracket or the like. The valve positioner 4 constitutes an electropneumatic converter 5 and a feedback mechanism 7 that is swingably inserted from a housing 6 toward an operating shaft 2. It has a feedback lever 8, the inner end of which is rotatably supported by a shaft 9, and the outer end is connected to the operating shaft 2 by a long hole 10 and a pin 11. Further, the valve positioner 4 incorporates the electropneumatic converter 5 including a nozzle flapper mechanism 12 and a magnet unit 13. The electro-pneumatic converter 5 has an input signal I0 (for example, 4 to 20 m).
(A) When the flapper 14 is swung around the fulcrum 15 by the magnet unit 13, the flapper 1
The back pressure of the nozzle 16 arranged close to and facing No. 4 changes, and this back pressure of the nozzle is amplified by the pilot relay 17 and output as the valve driving force.
When out is transmitted to the drive device 3, the drive device 3 is driven and the actuating shaft 2 is displaced in the vertical direction, whereby the valve opening degree of the automatic control valve 1 is adjusted. Further, the movement of the operating shaft 2 is received by the feedback lever 8 and fed back to the nozzle flapper mechanism 12, whereby the movement of the flapper 14 is stabilized.

The nozzle flapper mechanism 12 is provided with the flapper 14 whose middle portion is swingably supported by the fulcrum 15 and the nozzle 16 which is closely opposed to one end of the flapper 14, and is provided on the side opposite to the nozzle. Zero point adjustment mechanism 1
One end of a zero point adjusting spring 19 forming 8 is connected. The nozzle 16 is connected to an air supply source (not shown) via a supply air pipe 20, and has a constant (normally 1.4
The supply air pressure Psup of Kgf / cm ² ) is supplied. The pilot relay 17, the throttle 21, the pressure reducing valve 22, the pressure gauge for supply air (not shown) and the like are provided in the middle of the supply air pipe 20.

The feedback mechanism 7 has one end protruding outside the case 6 and connected to the operating shaft 2 in order to feed back the actual operation amount of the operating shaft 2 of the valve control valve 1 to the flapper 14. Lever 8
A span arm 25, one end of which is rotatably supported by a rotary shaft 23 and connected to the flapper 14 via a feedback spring 24; a span adjusting screw 26 attached to the span arm 25; A feedback plate 27 attached to the drive shaft 9,
The span adjusting screw 26 is movably mounted in the vertical direction, and the tip of the span adjusting screw 26 is in contact with the feedback plate 27.

The magnet unit 13 has a base 3
Yoke 31, coils 32a, 32 fixedly installed at 0
b, a permanent magnet 33 and the like. The yoke 31 is formed into a substantially E-shape when viewed from the front, so that the three legs 31 are formed.
a, 31b, 31c, the nozzle 16 is formed at the tip of one leg portion 31a located on the outside thereof in close proximity to the flapper 14, and the stopper 34 is provided at the tip of the other leg portion 31c. The permanent magnet 33 is arranged at the tip of the central leg portion 31b. As the permanent magnet 33,
For example, it is magnetized and formed so that the flapper 14 side has an N pole and the opposite side has an S pole. Here, the arrow a shown by the solid line in FIG. 4 is the direction of the magnetic field by the permanent magnet 33, and the arrow b shown by the broken line is the coil 32 in which the N pole and the S pole are obtained as illustrated.
The direction of the magnetic field by a and 32b is shown. Also, both coils 3
The polarities of 2a and 32b are set to be opposite.

A constant pressure (for example, 1.2 to
When the input signal I0 (4 mA to 20 mA) is applied to the coils 32a and 32b from the arithmetic unit while the supply air pressure Psup of 1.4 Kg / cm ² ) is supplied, the leg 31a on the left side of FIG. , A magnetic field is generated in the same direction as the magnetic field of the permanent magnet 33, and conversely, a magnetic field is generated on the right leg 31c side in a direction canceling the magnetic field strength of the permanent magnet 33. Therefore, the force F for attracting the flapper 14 on the left side increases, and the force on the right side weakens on the contrary, so that the counterclockwise rotation torque T proportional to the supply current I0 is generated in the flapper 14 about the fulcrum 15. Therefore, the flapper 14 swings and displaces counterclockwise about the fulcrum 15 to reduce the nozzle gap, in other words, to increase the nozzle ejection resistance. Therefore, the nozzle back pressure PN
The nozzle back pressure PN is increased by the pilot relay 17
And an air pressure signal proportional to the electric signal I0 is generated as the output pressure Pout.

The fulcrum 15 of the flapper 14 is provided near the central leg portion 31b of the yoke 31. Reference numeral 35 is a biasing spring means for biasing the flapper 14 toward the nozzle 16.

The pilot relay 17 belongs to the bleed type as a model because a part of the supply air pressure PSUP is constantly discharged to the atmosphere during normal operation. The inside of the pilot relay 17 has two diaphragms 37a, 37b, a partition wall 38, etc. 5 chambers, namely, air supply chamber 39 and output chamber 4
0, an atmosphere opening chamber 41, a bias chamber 42, and a nozzle back pressure chamber 43, and a housing 44, and a poppet valve 45.
And a piston 46 and the like held by the diaphragms 37a and 37b. The air supply chamber 39 is connected to the air supply source (not shown) via the supply air pipe 20 and is also connected to the nozzle 16. The output chamber 40 communicates with the air supply chamber 39 through a communication hole 48 provided in the partition wall 38, and the piston 4
A hole 49 provided at 6 allows communication with the atmosphere open chamber 41, and a pipe 50 connects to the drive device 3. The atmosphere opening chamber 41 forms an exhaust chamber and communicates with the outside of the housing 44. The supply air pressure PSUP is supplied to the bias chamber 42 via a pipe 52, and the nozzle back pressure PN is supplied to the back pressure chamber 43 via a pipe 53. The poppet valve 45 penetrates through the communication hole 48 so as to move back and forth, and controls the opening and closing of the communication hole 48 and the hole 49 of the piston 46.
Is urged in the closing direction, that is, the valve bodies provided above and below are closed in the direction of closing the communication hole 48 and the hole 49. The spring pressure of the spring 54 opposes the nozzle back pressure PN.

When such a pilot relay 17 is used as a normal operation type in which the output increases as the input increases, when the nozzle back pressure PN flowing from the pipe 53 into the back pressure chamber 43 increases, the diaphragms 37a and 37b are closed. Displaces downward. Therefore, the piston 46 descends against the bias spring 54, which causes the poppet valve 45 to move.
Also moves downward against the spring 54. As a result, the lower valve body of the poppet valve 45 is separated from the communication hole 48 of the partition wall 38 to communicate the air supply chamber 39 and the output chamber 40. Therefore, the supply air pressure PSUP supplied from the supply air pipe 20 to the air supply chamber 39 flows into the output chamber 40 through the communication hole 48, and the pressure in the output chamber 40 is the drive pressure Pou of the control valve 1.
It is supplied to the drive unit 3 through the pipe 50 as t.
On the other hand, when the nozzle back pressure PN is reduced from this state, the bias spring 54 causes the piston 46 to return upward, and the poppet valve 45 rises due to the urging force of the spring 54. At this time, since the upper valve body of the poppet valve 45 is separated from the lower end opening of the hole 49 of the piston 46 to communicate the output chamber 40 and the atmosphere opening chamber 41, the pressure in the output chamber 40 is set to the atmosphere opening chamber 41. And is discharged to the outside of the housing 44.

[0011]

The conventional valve positioner as described above has a problem that the operating point of the pilot relay changes due to a change in ambient temperature. That is, the cross spring 15a forming the fulcrum 15,
Since the fulcrum-constituting members such as the bracket 15b for supporting the spring 15a are made of stainless steel and the yoke 31 is made of a magnetic material, the linear expansion coefficients of these materials are slightly different from each other by about a factor of two. Therefore, when the ambient temperature changes, the nozzle gap increases and the nozzle back pressure decreases. As a result, the output air pressure Pout decreases (zero point shift), and the control valve cannot be controlled with high accuracy.

FIG. 5 is a diagram showing the characteristics of the electro-pneumatic converter (EPM) and the characteristics of the pilot relay. The solid line shows the characteristics under normal conditions, and the dotted line shows the characteristics due to changes in ambient temperature and creep. As is clear from this figure, when the ambient temperature changes, for example, the substantially horizontal state shown in FIG.
At the S position, the nozzle back pressure PN decreases from PN2 to PN1. Therefore, the output air pressure Pou of the pilot relay 44
The value of t decreases from P2 to P1, and this change is so large that it cannot be ignored.

Therefore, conventionally, when a zero point shift occurs due to a change in ambient temperature or the like, the zero point shift mechanism is adjusted by adjusting the force of the spring 19 by the zero adjusting mechanism 18. Is very tedious to adjust,
The problem was that it was annoying.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to change the output of the pilot relay irrespective of the change of the ambient temperature and the creep of the constituent members. The purpose of the present invention is to provide a positioner that can prevent the occurrence of zero point shift without requiring zero adjustment by an operator.

[0015]

In order to achieve the above object, the invention according to claim 1 provides a nozzle at one end of an outer leg portion of a yoke having an E-shaped cross section in which a coil and a permanent magnet are arranged. And a bias chamber facing the nozzle back pressure chamber for introducing back pressure of the nozzle, and an electropneumatic converter having a flapper having a fulcrum near the central leg of the yoke. In a positioner having a pilot relay provided with, a nozzle is formed in the central leg of the yoke facing the fulcrum of the flapper, and the back pressure of the nozzle is introduced into the bias chamber of the pilot relay. Is characterized by.

[0016]

In the present invention, the nozzle back pressure PN 'of the nozzle provided on the central leg of the yoke is guided to the bias chamber of the pilot relay. On the other hand, the nozzle back pressure PN of the nozzle formed on one leg of the yoke is guided to the back pressure chamber of the pilot relay. Therefore, when the nozzle back pressure PN changes due to the change in ambient temperature, PN 'also changes, and the characteristics of the pilot relay are moved in parallel (Fig. 2). In other words, the characteristics of the pilot relay are determined by these nozzle back pressures PN and PN 'introduced from the electropneumatic converter to the bias chamber and the back pressure chamber. Therefore, if the characteristics of the electropneumatic converter change due to changes in ambient temperature, As a result, the characteristics of the pilot relay will also change. Since the characteristic change at this time is a parallel movement, the output of the pilot relay does not change, and therefore the operating point of the control valve does not change.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is a sectional view showing a configuration of an electropneumatic converter and a pilot relay used in a positioner according to the present invention. In the figure, the same components as those in FIGS. 3 and 4 are designated by the same reference numerals, and the description thereof will be omitted. In this figure, in the present embodiment, the first nozzle 16 is formed on the tip end surface of one leg 31a on the outside of the yoke 31 installed and fixed on the base 30 so as to closely face the flapper 14, and the fulcrum of the flapper 14 is supported. The second nozzle 60 is formed at the tip of the central leg portion 31b corresponding to No. 15, and the second nozzle 60 is connected to the supply air pipe 20 through the throttle 61, and the back pressure PN of the nozzle 60 is increased. 'Is guided to the bias chamber 42 of the pilot relay 44. That is, in the present invention, instead of the supply air pressure Psup, the back pressure PN 'of the second nozzle 60 provided near the fulcrum 15 is guided to the bias chamber 42. Other configurations are the same as those of the above-described conventional device.

FIG. 2 is a diagram showing the characteristics of the electropneumatic converter and the pilot relay having such a configuration. In the figure, the characteristic of the electropneumatic converter changes from the characteristic indicated by the solid line to the characteristic indicated by the dotted line when the ambient temperature changes. At this time, the characteristic of the pilot relay changes from the characteristic indicated by the solid line to the characteristic indicated by the dotted line in accordance with the characteristic change of the electropneumatic converter. This characteristic change is a translation. This is because the back pressure PN 'of the second nozzle 60, which fluctuates due to the nozzle flapper gap, is guided to the bias chamber 41, which is a completely different point from the above-mentioned conventional device for guiding the constant supply air pressure Psup.

As described above, in the present invention, the characteristic of the pilot relay 44 is changed in accordance with the characteristic change of the electropneumatic converter 4. In other words, the characteristic of the pilot relay 44 is changed to the electropneumatic converter 13. To bias chamber 4
2 and the nozzle back pressures PN and PN 'introduced into the back pressure chamber 43, the 50% F.S. At the position S, even if the nozzle back pressure PN changes from PN2 to PN1 due to a change in ambient temperature, the characteristics of the pilot relay 44 only move in parallel, the output air pressure Pout does not change, and the operating point also changes. Absent. Therefore, no adjustment of the zero point shift is necessary.

[0020]

As described above, according to the positioner of the present invention, the cross section E in which the coil and the permanent magnet are arranged is provided.
An electro-pneumatic converter in which a nozzle is provided at one end of an outer leg of a character-shaped yoke, and a flapper having a fulcrum is provided near the central leg of the yoke facing the nozzle, and the nozzle. In a positioner equipped with a pilot relay provided with a bias chamber facing the nozzle back pressure chamber for introducing the back pressure of the nozzle, the nozzle is formed in the central leg of the yoke so as to face the vicinity of the fulcrum of the flapper. Since the back pressure of the nozzle is introduced into the bias chamber of the pilot relay, the characteristics of the pilot relay are moved in parallel with the changes in the characteristics of the electropneumatic converter due to changes in ambient temperature and creep of the fulcrum component. be able to. For this reason,
The output air pressure of the pilot relay does not change, and the zero point shift can be prevented. Therefore, it is possible to provide a positioner that does not require zero adjustment by an operator, is easy and easy to handle the positioner, and enables highly accurate control.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an electropneumatic converter and a pilot relay used in a positioner according to the present invention.

FIG. 2 is a diagram showing characteristics of an electropneumatic converter and a pilot relay according to the present invention.

FIG. 3 is a sectional view showing a conventional example of a valve positioner.

FIG. 4 is a diagram showing an operation principle of an electropneumatic converter.

FIG. 5 is a diagram showing characteristics of an electropneumatic converter and a pilot relay.

[Explanation of symbols]

5 ... Electro-pneumatic converter, 12 ... Nozzle and flapper mechanism, 14 ...
Flapper, 15 ... Support point, 16 ... Nozzle, 17 ... Pilot relay, 30 ... Base, 31 ... Yoke, 31a, 31
b, 31c ... Legs, 32a, 32b ... Coil, 33 ... Permanent magnet, 39 ... Supply air chamber, 40 ... Output chamber, 41 ... Atmosphere opening chamber, 42 ... Bias chamber, 43 ... Back pressure chamber, 60 ... Second
Nozzle.

Claims (1)

[Claims] 1. A cross section E in which a coil and a permanent magnet are arranged.
An electro-pneumatic converter in which a nozzle is provided at one end of an outer leg of a character-shaped yoke, and a flapper having a fulcrum is provided near the central leg of the yoke facing the nozzle, and the nozzle. In a positioner equipped with a pilot relay provided with a bias chamber facing the nozzle back pressure chamber for introducing the back pressure of the nozzle, a nozzle is formed in the central leg of the yoke facing the vicinity of the fulcrum of the flapper, and A positioner characterized by introducing back pressure of a nozzle into a bias chamber of the pilot relay.