JPH08100801A - Electro-pneumatic positioner - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize an electro-pneumatic positioner that is inexpensive and has a simple structure and that can control valve position of control valves having different characteristics with high stability and responsiveness. [Structure] A torque motor for displacing a flapper according to an input current, a nozzle opposed to the flapper, an air source for supplying air pressure to the nozzle via a throttle, and an output for amplifying the back pressure of the nozzle. A pilot relay that drives a control valve by air pressure, and a minor feedback loop that returns the displacement of this pilot relay valve to the flapper via a coil spring,
A feedback loop that returns the displacement of the valve of the control valve to the flapper, and in an electropneumatic positioner configured to control the displacement of the valve of the control valve in response to an input current, a coil spring of the minor feedback loop. It is characterized by being provided with an adjusting mechanism for continuously adjusting the spring constant by being screwed into one end.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an electropneumatic positioner used for controlling the valve position of a control valve,
Specifically, it is intended to obtain an arbitrary response characteristic according to the characteristic of the control valve with high stability.

[0002]

2. Description of the Related Art A control valve is constructed so as to determine the position of the valve according to an input current signal, and pneumatic pressure is used as auxiliary power, for example. Specifically, air pressure is applied to the upper part of the diaphragm, and the force is balanced with the force of the spring provided at the lower part of the diaphragm to determine the position of the valve. Here, the air pressure applied to the diaphragm is controlled by the current signal output from the regulator. Generally, an electropneumatic positioner is used to make the current signal and the valve position of the control valve proportional.

FIG. 3 is a structural explanatory view showing an example of such a conventional electro-pneumatic positioner. In the figure, reference numeral 1 is a torque motor that converts a current signal into an electromagnetic force, and is configured to excite a coil by an input current I applied from a regulator (not shown) or the like to drive a movable piece 11. The movable piece 11 is rotatably supported by a fulcrum 12.

Reference numeral 2 denotes a nozzle, which is paired with one end of the movable piece 11.
It is arranged so as to face, and there is no gap between it and the movable piece 11.
Configures the flapper mechanism. 3 is a non-bleed type
The exhaust valve 31 is installed in the case 32.
It is fixed via diaphragms 33 and 34. 35
Is a poppet valve, one end of which is a case through a coil spring 36
It is fixed at 32. 37 is a fixed diaphragm,
Between the case 32 and the diaphragm 33 via the constant diaphragm 37
Supply air pressure signal P to _SHas been added. Also supply empty
Barometric pressure signal P_SIs a diamond without the fixed diaphragm 37
Between flams 33 and 34 and on the intake valve side of poppet valve 35
Has been added to each. The structure configured in this way
The Ylot relay 3 has a back pressure P of the nozzle 2. _bOutput pressure P_OWhen
And then function to amplify.

A control valve 4 receives the output pressure P _O of the pilot relay 3 as power.
Reference numeral 5 is a feedback mechanism for returning the displacement signal of the stem 41 of the control valve 4 to the movable piece 11. This return mechanism 5
Is composed of a rotary shaft 51, an L-shaped lever 52, and a coil spring 53. A cut groove 54 is provided at one end of the lever 52, and a pin 42 attached to the stem 41 of the control valve 4 is fitted and coupled to the cut groove 54, and a corner portion is rotatably attached to the rotary shaft 51. And the other end is movable piece 11 via a coil spring 53.
It is connected to.

Reference numeral 6 is a lever, one end of which is attached to the exhaust valve 31 of the pilot relay 3 and the other end of which is a coil spring 7.
Is connected to the movable piece 11 via. Reference numeral 8 denotes a zero point adjusting mechanism, which includes a rotary knob 81, a coil spring 82, and a moving body 83.
It is composed of One end of the coil spring 82 has a movable piece 11
And the other end is attached to a moving body 83 that moves in accordance with the rotation of the rotary knob 81. As a result, the coil spring 82 expands and contracts according to the rotation direction of the rotary knob 81.

The operation of such a configuration will be described. Assuming that the current I is input to the torque motor 1 and the movable piece 11 is displaced in the X direction closing the nozzle 2, the back pressure P _{b of the} nozzle 2 is generated.
Moves up and moves the exhaust valve 31 to the left,
With the left end of the poppet valve 35 in contact with the poppet valve 3
Move 5 to the left. This movement changes the opening of the intake valve and increases the output pressure P _{O of the} air. As the air output pressure P _O increases, the control valve 4
Stem 41 is displaced in the W direction. The displacement of the stem 41 in the W direction is returned to the movable piece 11 via the lever 52 and the coil spring 53, and the force pulling the movable piece 11 is reduced. This decrease in force acts in the direction of opening the gap between the movable piece 11 and the nozzle 2. By repeating such a series of operations, the current I and the position of the stem 41 are balanced, and the stem 41 stops at the position according to the value of the current I.

On the other hand, when the nozzle back pressure P _b input to the pilot relay 3 increases, the exhaust valve 31 moves to the left, and the movable piece 11 is lowered via the lever 6 and the coil spring 7 in a direction to lower the nozzle back pressure P _b. Shift to. By repeating such an operation, the position of the exhaust valve 31 is balanced corresponding to the current I. That is, a minor feedback loop is formed as shown in FIG.

This minor feedback loop is provided for the following purpose. In general, the time constant of the control valve 4 is larger than that of other elements constituting the positioner, and the feedback signal according to the displacement of the stem 41 also has a large delay. Therefore, the displacement signal of the exhaust valve 31 of the pilot relay 3 having a small delay, which is the previous component, is negatively fed back. This can improve the stability and response characteristics of the entire control loop.

By the way, there are many sizes and types of control valves which are controlled by using the electropneumatic positioner, and the characteristics of the drive valves and the frictional force of the gland packing are greatly different and their characteristics are not constant. In order to improve the control stability and response characteristics of these valves, it is necessary to individually adjust the gain of the minor feedback loop according to the valve as described above.

In adjusting the gain of the minor feedback loop, it is possible to prepare a large number of coil springs having different spring constants and select a coil spring having a spring constant suitable for the valve characteristics.

[0012]

However, there is a limit to the types of coil springs that can be prepared, and since the spring constant can only be changed in steps, it is not possible to change the gain continuously. Therefore, there is a problem that optimum adjustment cannot be performed. In addition, as a result, it is not preferable to prepare a large number of coil springs that are not used and have different spring constants, which causes a cost increase.

Further, there is a problem that it takes a considerable amount of work to select and install or replace the coil spring suitable for the characteristics for each valve. The present invention solves the above-mentioned conventional problems, and an object thereof is an electropneumatic valve which can control valve position of control valves having different characteristics with high stability and responsiveness with an inexpensive and simple structure. It is about realizing a positioner.

[0014]

SUMMARY OF THE INVENTION An electropneumatic positioner of the present invention comprises a torque motor for displacing a flapper according to an input current, a nozzle arranged to face the flapper, and air for supplying air pressure to the nozzle via a throttle. Source, a pilot relay that amplifies the back pressure of the nozzle and drives the control valve by its output air pressure, a minor feedback loop that returns the displacement of this pilot relay valve to the flapper via a coil spring, and a valve of the control valve. In the electropneumatic positioner configured to control the displacement of the control valve in response to the input current, the feedback loop returning the displacement of the minor feedback loop to the flapper, and screwing it to one end of the coil spring of the minor feedback loop. The adjustment mechanism that continuously adjusts the spring constant. And wherein the digit.

[0015]

The spring constant of the coil spring forming the minor feedback loop continuously changes according to the screwing length of the adjusting mechanism screwed on one end. Thus, the gain of the minor feedback loop can be continuously changed within the adjustable range of the spring constant, and the valve position control of the control valves having different characteristics can be performed with high stability and responsiveness.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a structural explanatory view showing a main part of an embodiment of the present invention, and the same parts as those in FIG. 3 are designated by the same reference numerals.
In the figure, 9 is an adjusting screw that functions as a mechanism for adjusting the spring constant of the coil spring 7 that forms a minor feedback loop. This screw 9 is a screw hole 61 of the lever 6.
And the end of the coil spring 7 is screwed into one end of the coil spring 7. The other end of the coil spring 7 is fitted into a convex portion provided on the movable piece 11. That is,
The lever 6 and the movable piece 11 are connected via a coil spring 7 and an adjusting screw 9.

In such a structure, by rotating the adjusting screw 9 in the clockwise direction, the end portion of the adjusting screw 9 is screwed into the inner diameter portion of the end portion of the coil spring 7, so that the coil spring 7 can expand and contract. The length L (hereinafter referred to as the effective length) becomes short. Here, the spring constant K is expressed by the following equation. K = however _{^{G · d 4 / 8N a ·}} D 3, G: modulus of rigidity of the coil spring material d: coil spring wire diameter N _a: effective turns D: average diameter of the coil coil spring [(outer diameter + inner diameter) / 2] Further, when the pitch of the coil spring 7 is P, the following relationship holds.

N _a = L / P From these, the relation of K = G · d ⁴ · P / 8L · D ³ is established, and the spring constant K can be continuously changed by rotating the adjusting screw 9. it is obvious.

FIG. 2 is a block diagram of a minor feedback loop having such a mechanism for adjusting the spring constant of the coil spring 7. As is apparent from the figure, by rotating the adjusting screw 9, the spring constant K of the coil spring 7 can be continuously changed, the gain of the minor feedback loop can be continuously changed, and various kinds of different characteristics can be obtained. Optimal valve position control with high stability and responsiveness to the control valve 4 can be realized easily at low cost.

Further, when the adjusting screw 9 is rotated, the force returned to the movable piece 11 changes when the movable piece 11 and the lever 6 have the same positional relationship before and after the adjustment screw 9 is rotated. The balance of the force applied to the movable piece 11 is changed, and the stem 41 of the control valve 4 is displaced even if the same input current is applied. This corresponds to the zero point change of the electropneumatic positioner, and the zero point adjustment is required. Here, the pitch of the screw groove provided in the adjusting screw 9 is attached so that the coil spring 7 can expand and contract over the entire length when the output of the positioner is zero, that is, when the displacement of the stem 41 of the control valve 4 is zero. If the pitch of the coil spring 7 at the time of turning is equal, the force applied to the movable piece 11 does not change even if the adjusting screw 9 is rotated, and it is not necessary to perform zero point adjustment.

In the above description, the coil spring 7 is a compression coil spring, but it may be a tension coil spring. Further, the spring constant adjusting mechanism is not limited to the adjusting screw, and may be a pin having an equivalent function.

[0022]

As described above, according to the present invention,
It is possible to realize an electropneumatic positioner that is inexpensive and has a simple structure and that can control the valve position of control valves having different characteristics with high stability and responsiveness.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view showing a main part of an embodiment of the present invention.

FIG. 2 is a block diagram of a minor feedback loop including the spring constant adjusting mechanism of FIG.

FIG. 3 is a configuration explanatory view showing an example of a conventional electropneumatic positioner.

FIG. 4 is a block diagram of the feedback loop of FIG.

[Explanation of symbols]

 1 Torque Motor 2 Nozzle 3 Pilot Relay 4 Control Valve 5 Feedback Mechanism 6 Lever 7 Coil Spring 8 Zero Adjustment Mechanism 9 Adjustment Screw

Claims (1)

[Claims] 1. A torque motor for displacing a flapper according to an input current, a nozzle opposed to the flapper, an air source for supplying air pressure to the nozzle via a throttle, and an amplifier for amplifying the back pressure of the nozzle. It has a pilot relay that drives the control valve by its output air pressure, a minor feedback loop that returns the valve displacement of this pilot relay to the flapper via a coil spring, and a feedback loop that returns the displacement of the control valve valve to the flapper. Then, in the electropneumatic positioner configured to control the displacement of the control valve in response to the input current, an adjusting mechanism that is screwed onto one end of the coil spring of the minor feedback loop to continuously adjust the spring constant. An electro-pneumatic positioner characterized by being provided with.