JPH0828734A - Electric-pneumatic converter - Google Patents

Abstract

PURPOSE:To advance a lag caused in driving an object to be controlled and restrain overshoot or the like in an electric-pneumatic converter for converting an input electric signal to output air pressure corresponding to a value of input electric signal by providing a dynamic characteristics converting means for converting the dynamic characteristic of output air pressure for the input electric signal to any dynamic characteristic. CONSTITUTION:In an apparatus for converting an input electric signal Iin to output air pressure Po corresponding to a value of the electric signal to adjust the opening of an adjusting valve 2, an electric-pneumatic converter 1' is provided with a dynamic characteristic converting section 1'-2. When a lag may be generated in driving the opening of the valve and overshoot or the like may be caused in the opening of the valve since the volume of an actuator of the adjusting valve 2 is small, the dynamic characteristics of the output air pressure Po for the input electric signal Iin is converted to any dynamic characteristic by adjusting the transmission function of the dynamic characteristic converter 1'-2. Thus, the transmission property of the adjusting valve 2 is quickened and stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electropneumatic converter for converting an input electric signal into an output air pressure corresponding to the value of the electric signal.

[0002]

2. Description of the Related Art Conventionally, this type of electropneumatic converter (I /
P) is used in a control valve drive system as shown in FIG. In this system, the electropneumatic converter 1 converts the input electric signal I _in (4 to 20 mA) into an output air pressure Po according to the value of the electric signal. The converted output air pressure Po is given to the control valve (CV) 2. This allows
The valve opening degree V of the control valve 2 is adjusted to an opening degree according to the input electric signal I _in .

[0003]

However, in such a CV drive system, when the transfer characteristic of the control valve 2 is slow or the actuator of the control valve 2 has a small volume, overshoot or hunting occurs. There was a problem with the response.

The present invention has been made in order to solve such a problem, and its object is to prevent the delay, overshoot, hunting and the like from occurring during the driving of the controlled object, and to set it. An object of the present invention is to provide an electropneumatic converter capable of shortening the time.

[0005]

In order to achieve such an object, the present invention provides a dynamic characteristic conversion means for converting a dynamic characteristic (responsiveness) of output air pressure to an input electric signal into an arbitrary dynamic characteristic. It is provided in the empty converter.

[0006]

Therefore, according to the present invention, the dynamic characteristic of the output air pressure with respect to the input electric signal can be set to an appropriate dynamic characteristic to accelerate the delay occurring when the controlled object is driven, and to suppress the overshoot and hunting.

[0007]

EXAMPLES The present invention will now be described in detail based on examples. FIG. 1 is a block diagram showing an outline of a control valve drive system to which an embodiment of the present invention is applied. In this embodiment, the electro-pneumatic converter 1'is provided with the dynamic characteristic conversion unit 1'-2, and the transfer function of the dynamic characteristic conversion unit 1'-2 is adjusted to output the air pressure Po to the input electric signal I _in . It is assumed that the dynamic characteristics of can be converted into arbitrary dynamic characteristics. In the figure, 1'-1 is a transfer characteristic portion of the conventional electropneumatic converter 1.

FIG. 2 shows a specific functional block diagram of the electropneumatic converter 1 '. In the figure, 1'-11 is an input signal processing unit, 1'-12 is an electropneumatic conversion mechanism, 1'-13 is a pressure sensor, 1'-14 is a subtractor, and blocks having these components are Transfer characteristic part 1'-1 of the conventional electropneumatic converter 1
Equivalent to. In this electro-pneumatic converter 1 ', the dynamic characteristic converter 1'-2 includes an input signal processor 1'-11 and a subtractor 1'.
It is provided between -14 and. In addition, the input signal processing unit 1′-11 converts the input electric signal I _in into a value of 0 to 100%, that is, converts a current value of 4 to 20 mA into a value of 0 to 100%, and converts the converted value into a% value. A corresponding set pressure value is given to the subtractor 1'-14 via the dynamic characteristic conversion unit 1'-2. The subtractor 1'-14 takes the difference between the set pressure value given via the dynamic characteristic conversion unit 1'-2 and the actual output air pressure Po detected by the pressure sensor 1'-13, and the difference (deviation value) ) To the electropneumatic conversion mechanism 1'-12. Thereby, the electropneumatic conversion mechanism 1′-12 generates the output air pressure Po so that the deviation value in the subtractor 1′-14 becomes zero.

FIG. 3 is a block diagram showing the control valve drive system shown in FIG. 1 as a transfer function.
In the figure, C (s) is the transfer function of the dynamic characteristic conversion unit 1′-2, D (s) is the transfer function of the transfer characteristic unit 1′-1, and V is
(S) is the transfer function of the control valve 2. In this case, since there is no gain attenuation or phase shift within the band of the system including the electropneumatic converter 1'and the control valve 2, D (s) = 1 is simplified. Generally, V (s) and C (s) can be expressed by the following equations (1) and (2). In these equations, ζ is a damping coefficient, ω ₀ is a natural angular frequency, s is a Laplace variable, and a and b are parameters. Here, in the present embodiment, the transfer function C of the dynamic characteristic conversion unit 1′-2 is set so that the transfer characteristic of the control valve 2 is substantially improved.
(S) is set to an appropriate value.

[0010]

[Equation 1]

[When the Transmission Characteristic of the Control Valve 2 is Slow] For example, when the transmission characteristic of the control valve 2 is slow and the valve opening V is delayed, the transmission characteristic of the control valve 2 needs to be accelerated.
The slow transmission characteristic of the control valve 2 corresponds to the case of ζ> 1 or ζ >> 1 in the equation (1). In this case, V (s) is expressed by the following equation (3). However, in this equation, A and B are real numbers, and A <B.

[0012]

[Equation 2]

When the equation (3) is expressed by a board diagram, it has a characteristic I shown in FIG. In order to speed up the transmission characteristic of the control valve 2, this characteristic I should be improved to the characteristic II as shown in FIG. In this case, the transfer function C
In equation (2) showing (s), a is set so that a = A
By selecting the value of, the characteristic I can be substantially the characteristic II. This can be expressed as follows. Note that b is usually set to about 10 times as large as a.

[0014]

(Equation 3)

[When the Volume of Actuator of Control Valve 2 is Small] For example, when the volume of the actuator of the control valve 2 is small and overshoot or hunting occurs in the valve opening V, it is necessary to stabilize this. The occurrence of overshoot and hunting in the valve opening V corresponds to the case of 0 <ζ <1 in the equation (1). In this case, V
(S) is not multiplied like the expression (3), and if expressed by the expression (3), A and B are complex numbers. When this equation is expressed by a board diagram, it becomes like a characteristic III shown in FIG. In this characteristic III, ω _p is the peak angular frequency, M
_p is the peak gain. ω _p and M _p are expressed by the following expressions.

[0016]

[Equation 4]

In order to stabilize the overshoot and hunting of the valve opening V, this characteristic III should be improved to the characteristic IV as shown in FIG. In this case, the transfer function C (s)
In the equation (2), the characteristic III can be substantially the characteristic IV by selecting b so that the gain of C (s) is 1 / M _p when ω = ω _p . However, usually a
Select >> b. Actually, b may be adjusted so that the step response of the system including the electropneumatic converter 1'and the control valve 2 does not overshoot.

That is, in this embodiment, the transfer function C (s) of the dynamic characteristic conversion unit 1'-2 is C (s) = (b / a).
It is expressed as (s + a) / (s + b), and for example, when it is desired to shorten the delay, a <b (or a << b),
It suffices that a = A (A is a time constant of the delay of the control valve 2), and to suppress hunting, a> b (or a >>).
b) and b may be values smaller than ω _p (value at which the gain of C (s) is 1 / M _p at ω = ω _p ).

In this embodiment, the case where the delay occurs when the valve opening V is driven, the case where the overshoot and the hunting occur, are described, but the dynamic characteristic conversion unit 1'-2.
By appropriately determining the transfer function C (s) of the control valve 2 under various circumstances, the transfer characteristic of the control valve 2 can be substantially improved, and the time until settling can be shortened. become. Further, in the present embodiment, the control target is the valve opening, but it is not limited to the valve opening, and various control targets (for example, the flow rate, pressure, temperature, liquid of the process control system including the control valve, liquid, etc. Surface) is considered.

[0020]

As is apparent from the above description, according to the present invention, the electro-pneumatic converter is provided with the dynamic characteristic converting means for converting the dynamic characteristic of the output air pressure with respect to the input electric signal into an arbitrary dynamic characteristic. , By setting the dynamic characteristics of the output air pressure to the input electric signal as appropriate dynamic characteristics, it becomes possible to speed up the delay that occurs when driving the controlled object, suppress overshoot and hunting, and reduce the time until settling. It can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a control valve drive system to which an embodiment of the present invention is applied.

FIG. 2 is a specific functional configuration diagram of an electropneumatic converter in the control valve drive system.

FIG. 3 is a block diagram showing a transfer function of the control valve drive system.

FIG. 4 is a board diagram showing a transfer function V (s) when a delay occurs when driving the valve opening.

5 is a diagram showing a characteristic of a transfer function C (s) for making the characteristic I of the transfer function V (s) shown in FIG. 4 substantially a characteristic II.

FIG. 6 is a board diagram showing a transfer function V (s) when hunting occurs when the control valve is driven.

7 is a diagram showing characteristics of a transfer function C (s) for making the characteristic III of the transfer function V (s) shown in FIG. 6 substantially a characteristic IV.

FIG. 8 is a block diagram showing an outline of a conventional control valve drive system.

[Explanation of symbols]

1 '... electro-pneumatic converter, 1'-1 ... Transfer characteristic part of conventional electro-pneumatic converter, 1'-2 ... Dynamic characteristic conversion part, 1'-11 ... Input signal processing part, 1'-12. Empty conversion mechanism, 1'-13 ... Pressure sensor, 1'-14 ... Subtractor, 2 ... Control valve.

Claims (3)

[Claims] 1. An electropneumatic converter for converting an input electric signal into an output air pressure according to a value of the electric signal, wherein a dynamic characteristic conversion for converting a dynamic characteristic of the output air pressure with respect to the input electric signal into an arbitrary dynamic characteristic. An electropneumatic converter comprising means. 2. An input signal processing means for converting an input electric signal into a% value according to the value of the electric signal and outputting a set pressure value according to the% value, and a set pressure output by the input signal processing means. An electropneumatic converter including subtraction means for taking the difference between the value and the actual output air pressure detected by the pressure sensor, and electropneumatic conversion means for producing the output air pressure so that the difference in the subtraction means becomes zero. In the electro-pneumatic method, a dynamic characteristic converting means for converting the dynamic characteristic of the output air pressure with respect to the input electric signal into an arbitrary dynamic characteristic is provided between the input signal processing means and the subtracting means. converter. 3. The electropneumatic converter according to claim 1, wherein the output air pressure is output for driving the control valve.