KR101724017B1 - Pneumatic type digital process controller - Google Patents

Pneumatic type digital process controller Download PDF

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Publication number
KR101724017B1
KR101724017B1 KR1020150149679A KR20150149679A KR101724017B1 KR 101724017 B1 KR101724017 B1 KR 101724017B1 KR 1020150149679 A KR1020150149679 A KR 1020150149679A KR 20150149679 A KR20150149679 A KR 20150149679A KR 101724017 B1 KR101724017 B1 KR 101724017B1
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Prior art keywords
value
valve
delta
load
vent
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KR1020150149679A
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Korean (ko)
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김영석
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주식회사 비와이
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B11/00—Automatic controllers
    • G05B11/01—Automatic controllers electric
    • G05B11/36—Automatic controllers electric with provision for obtaining particular characteristics, e.g. proportional, integral, differential
    • G05B11/42—Automatic controllers electric with provision for obtaining particular characteristics, e.g. proportional, integral, differential for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.

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  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Fluid-Driven Valves (AREA)

Abstract

Provided is an electronic pneumatic control device for controlling displacement of a diaphragm. The electronic pneumatic control device includes: a PID modulation device for comparing the output value of the process variable controlled by the diaphragm and the set target value every predetermined cycle to generate a control input signal for opening and closing a load valve or a vent valve; a critical subtractor for decreasing the absolute value of the value by adding or subtracting the threshold value (S) is added or subtracted from the accumulated air flow accumulated value when the required air flow rate is accumulated every predetermined cycle and the required air flow accumulated value exceeds a predetermined threshold value to open the load valve or vent valve; and a load/vent selector for generating a signal for opening the load or vent valve according to the output value of the critical subtractor; a load output generating device for controlling the load valve to be opened for a predetermined period when the accumulated air flow rate is greater than the upper limit value (+S); and a vent output generator for controlling the vent valve to open for a predetermined period when the cumulative air flow rate is less than the lower limit value. Thus, the electronic pneumatic control device can adjust the displacement of the diaphragm more stably by adjusting the opening and closing time of the rod and vent valve in response to the change of the driving voltage supplied to the rod and vent valve.

Description

[0001] PNEUMATIC TYPE DIGITAL PROCESS CONTROLLER [0002]

The present invention relates to an electronic control apparatus, and more particularly, to an electronic pneumatic control apparatus for converting an electric feedback signal into an air pressure and outputting it in controlling a process control variable.

An electronic pneumatic control device is used to control control parameters such as pressure, temperature, or oil level. Generally, an electronic pneumatic control device has means for receiving an electrical signal from a sensing device that measures the current value of a management variable and means for generating a signal for control of the controlled device.

In order to control the opening and closing amount of the diaphragm valve to maintain the output value of the process control variable at the target value, the present output value of the process control variable and the target value A control device is needed to adjust the displacement of the diaphragm valve by calculating the error between the values.

A pneumatic controller using only air pressure is used as a control device for controlling the displacement of the diaphragm valve. Recently, an electronic control type pneumatic control device has been used. However, the use of analog control circuits is on the rise, mainly due to the need for precise mechanics and the need for periodic maintenance.

Due to these problems, analog type electronic pneumatic control devices have been introduced in the field, but digital electronic pneumatic control methods have recently emerged due to the development of malfunction prevention circuit technology for digital control systems.

On the other hand, the electronic pneumatic control device regulates the displacement of the diaphragm valve by regulating the air pressure inside the diaphragm. A load valve and a vent valve And the air pressure inside the diaphragm is adjusted by opening and closing the valves for a predetermined time, thereby controlling the opening and closing amount of the diaphragm valve.

The conventional electromagnetic pneumatic control apparatus does not adopt a method of passing a small amount of air proportionally linearly through the above-mentioned rod / vent valve due to trouble and maintenance, and simply adopts an on / off method. Therefore, to fill or reduce the amount of air in the diaphragm at a desired rate, it is necessary to appropriately modulate the on / off time of the valve.

Furthermore, even if the valve is a high-speed operation valve, the on / off delay time is several tens of milliseconds, and therefore, the time required for opening the valve at least once should be at least several tens of milliseconds.

The present invention provides an electronic pneumatic control device capable of stably controlling the air pressure of the diaphragm even when the driving voltage for controlling the rod / vent valve is unstable.

The present invention provides an electropneumatic control device for linearly controlling the amount of air flowing in and out through a rod / vent valve for diaphragm air pressure control.

According to an exemplary embodiment of the present invention, a rod valve and a vent valve that are connected to a diaphragm and can be turned on and off are mounted, and the air pressure inside the diaphragm is adjusted by opening and closing the rod valve and the vent valve for a calculated time The electromagnetic pneumatic control device for controlling the displacement of the diaphragm compares the output value of the controlled variable controlled by the diaphragm and the set target value for each predetermined period (DELTA T) to calculate the required air flow rate to be supplied to the diaphragm A proportional integral derivative control (PID) modulation device for generating a control input signal for opening and closing a load valve or a vent valve; The necessary air flow accumulation value exceeds the range of the predetermined threshold value? S indicated by the upper limit value (+ DELTA S) or the lower limit value (- DELTA S) while accumulating the necessary air flow rate every predetermined period (DELTA T) A critical subtractor for decreasing the absolute value of the accumulated value by subtracting or adding the threshold value? S from the required air flow accumulation value when the load valve or the vent valve is opened for a predetermined period? T; When the output value of the critical subtractor is larger than the predetermined upper limit value (+ DELTA S), a control signal for opening the load valve is generated. When the output value of the critical subtractor is smaller than the lower limit value (- DELTA S) Selector; When the cumulative air flow rate is greater than the upper limit value (+ DELTA S), a load is selected from the load / vent selector to generate a digital pulse signal having a fixed pulse width so as to open the load valve for a predetermined period An output generating device; And when the cumulative air flow rate is smaller than the lower limit value (- DELTA S), a digital pulse signal having a fixed pulse width is selected so as to open the vent valve for a predetermined period (DELTA T) And the displacement of the diaphragm can be adjusted more stably by controlling the opening and closing times of the rod and vent valves in response to the change of the driving voltage supplied to the rod and vent valves.

On the other hand, if the driving voltage supplied to the solenoid for controlling the rod / vent valve is lowered, the time required for fully opening and closing the valve may be increased. This phenomenon can sometimes occur when the voltage and the other components in the control device are commonly used in addition to the solenoid.

Accordingly, if the valve opening / closing time (DELTA T) is not adjusted in a state where the driving voltage supplied to the solenoid is lowered, the amount of air flowing in and out of the valve once is reduced or even the valve is not opened. It can fall.

In the present invention, the predetermined period, that is, the opening / closing time of the rod / vent valve, can be adjusted by adjusting the selected threshold value? S for more stable displacement control of the diaphragm.

Specifically, the threshold value (△ S ') of the adjusting control by the change of the driving voltage △ S (△ Q / △ Q 0) , where △ S is the threshold value before the regulation, △ Q 0 is the driving Q is the amount of air flowing in and out during the opening / closing time when the driving voltage is changed.

Hereinafter, the derivation process of adjusting the threshold value will be described. First, T is a function value for the driving voltage (V 0 ), and T = g (V 0 ). The air flow rate through the valve once the valve is opened is a function value for T and P (pneumatic magnitude) and is Q = f (T, P 0 ). From these two functions, it can be confirmed that? Q = h (V, P).

Required air flow

Figure 112015104461297-pat00001
Assuming that a constant u i value is maintained, n times of T time elapses, the voltage is maintained at V 0 , the pneumatic pressure is maintained at P 0 , and if m loads are performed,
Figure 112015104461297-pat00002
.

The equation

Figure 112015104461297-pat00003
And
Figure 112015104461297-pat00004
, And if n is large,
Figure 112015104461297-pat00005
And
Figure 112015104461297-pat00006
. ≪ / RTI > Therefore, the ratio of the number m of valve openings in total n times is the required air flow rate
Figure 112015104461297-pat00007
This fact shows that a controller that performs valve opening and closing operations by a predetermined time T can control the valve opening / closing amount proportionally to the required air flow rate.

However, if the amount of air entering and exiting the valve changes once due to the change in voltage and air pressure

Figure 112015104461297-pat00008
Is not flowing,
Figure 112015104461297-pat00009
.

Therefore, even if the voltage and the air pressure change,

Figure 112015104461297-pat00010
≪ RTI ID = 0.0 >
Figure 112015104461297-pat00011
.

The electromagnetic pneumatic control device according to the present invention adjusts the opening and closing time of the rod and vent valve in accordance with the change of the driving voltage supplied to the rod and vent valve so that even if the characteristic of the valve opening / It is possible to stably adjust the displacement of the diaphragm without changing the control characteristic without changing the input signal.

The electromagnetic pneumatic control device according to the present invention employs a digital signal processing PID control method, and includes a critical subtracter, a load / vent selector, and the like, so that the diaphragm opening / closing amount is linearly controlled to a required air flow rate.

In addition, the electromagnetic pneumatic control apparatus according to the present invention has a built-in critical subtracter that limits the absolute value of the accumulated air flow rate to a predetermined value or less, Minimize delays.

1 is a block diagram of a digital electronic pneumatic control device of the present invention.
2 is a block diagram of a digital control apparatus using a pulse pulse having a fixed pulse width according to the present invention.
3 is a block diagram of a digital linear control apparatus according to the present invention.
4 is a timing chart showing an embodiment of the valve opening / closing control according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments. For reference, the same numbers in this description refer to substantially the same elements and can be described with reference to the contents described in the other drawings under these rules, and the contents which are judged to be obvious to the person skilled in the art or repeated can be omitted.

1 is a diagram showing an electronic pneumatic control device according to the present invention.

Referring to FIG. 1, when an electric signal transmitted from a standard type transmitter 120 and a resistance temperature detector (RTD) sensor 123 having 4 to 20 mA is fed back as feedback, Thereby controlling the flow control valve 138. The electromagnetic pneumatic control apparatus according to the present invention converts an alternating current of 110 or 220 V supplied from an external power supply source 100 into a direct current power supply 24 V from a direct current transformer 112 and supplies it to a transmitter So that no separate DC power supply is required.

Referring to FIG. 1, a signal transmitted from the transmitter 120 and the RTD sensor 123 is received and compared with the set target value 110 determined by the user. At this time, when a difference between the set value and the input signal occurs, the PID controller 132 causes the pulse modulation module 133 to generate a pulse signal.

The solenoid drive 134 increases or decreases the air pressure in accordance with the output voltage pulse signal 24V of the pulse generation module. One of the pneumatic solenoid valves increases the output air pressure, and the other causes air to be released into the atmosphere. In this way, each time an electrical pulse signal is received, the air pressure inside the diaphragm of the control valve will gradually increase or decrease.

When the signal difference is large, the solenoid valve is opened for a long time to accelerate the change of the input / output speed of the air, and when the signal difference is small, the electric pulse width is reduced to prevent the transient operation. Further, the electromagnetic pneumatic control device is provided with malfunction warning means 128 on the outside. The external malfunction alarm means 128 turns off the solenoid drive 134 while turning on the lamp 129 when an abnormality is detected.

The digital pneumatic control device according to the present invention controls the pneumatic valve using a digital central processing unit 126. The digital central processing unit 126 includes digital signal filters 115 and 130 and a PID controller 132, A modulation module 133, a data communication interface 125, an internal malfunction alarm unit 127 for controlling external malfunction alarm means, and the like.

The digital signal filter 115 is provided with an external setpoint input 110 of 4 to 20 mA through an amplifier 111. The internal set point store 116 is also connected to the mode selector 109 and the up-down switch 117.

The electronic pneumatic control apparatus according to the present invention includes storage means for storing operating software for driving the digital central processing unit 126, and a flash memory device can be used. In addition, a digital signal processor may be used as a preferred embodiment of the digital central processing unit 126 according to the present invention.

The digital signal filter 130 filters the electrical signal transmitted from the transmitter or RTD sensor and is applied to the input 131 of the PID controller. The PID controller compares the set target value with the current value of the feedback process management variable to generate the PID control signal. The electronic pneumatic control device can be controlled by the external computer 124 using the RS232C or RS485 system 125 data interface.

The electromagnetic pneumatic control device according to the present invention can transmit the control value through the signal transmitter 141 and is connected to the standard transmitter 120 and the digital signal filter 130. In addition, the electronic pneumatic control device can display current control information by using the LCD display device 114 or other display device. The pulse frequency module 133 may use a pulse width modulation type or a pulse frequency modulation type pulse modulation type generator. As the pulse width modulation method according to the present invention, a method of adjusting the air flow rate by adjusting the width of the pulse in proportion to the difference between the set value and the function value of the current process variable may be used. The pulse frequency modulation method may be a method of controlling the flow rate of air by adjusting the frequency of pulses in proportion to the difference between the set target value and the current process variable value.

2 is a block diagram of a digital control apparatus using a pulse pulse having a fixed pulse width according to the present invention. Referring to FIG. 2, the current process variable output value 220 transmitted from the controlled processing device 250 is received and compared with the set target value 210 determined by the user. At this time, when a difference 221 between the set value and the input signal occurs, the PID modulation module 230 generates a vent output for controlling the load output generator 231 or the vent valve 241 for controlling the rod valve 240 Thereby activating the device 232.

The load output generating device 231 or the vent output generating device 232 is connected to the diaphragm valve 245 which is turned on / off at high speed by converting the period of the pulse using a pulse having a fixed time width of? And the like.

3 is a block diagram of a digital linear control apparatus according to the present invention. Referring to FIG. 3, the current process variable output value 320 transmitted from the controlled processing device 398 is received and compared with the set target value 310 determined by the user. The air flow rate to be supplied to the diaphragm of the diaphragm valve 395 according to the PID modulation module 330 that calculates and controls the error 321 between the target value 310 and the measured value 320 at every? Flow rate) is determined, and the air flow rate has a continuous value and may be a physical quantity having a positive or negative value. For example, in the case of a positive number, the rod output 390 may be operated using the load output generator 371, and the vent valve 391 may be operated using the vent output generator 372 if the load output is negative.

In addition, when the rod valve 390 or the vent valve 391 is once opened once, a certain time (for example, 20 ms) is required to be kept open. At the same time, In the present embodiment, as a method for keeping the load valve 390 or the vent valve 391 open for a predetermined time and at the same time making the average air flow equal to the required air flow rate, And an electronic pneumatic control device 380 for digitally linearly proportional-controlling the electric power.

Referring again to FIG. 3, if it is assumed that the time ΔT is the time when the valve is opened during the load or vent, in order to increase the opening time interval, the required air flow rate is accumulated every ΔT time, When the flow rate is larger than the upper limit value (+ DELTA S), the load valve is opened for DELTA T time.

On the other hand, when the cumulative air flow rate is smaller than the set lower limit value (- DELTA S), the vent valve is opened for DELTA T time. Such operation is determined by the load / vent selector 370, and the load output generator 371 or the vent output generator 372 generates a pulse.

Further, the required air flow accumulation value exceeds the threshold value range indicated by the upper limit value (+ DELTA S) or the lower limit value (- DELTA S), and the load valve 390 or the vent valve 391 is opened In this case, the absolute value of the accumulated value, that is, the range of change of the accumulated value is reduced by subtracting or adding the threshold value? S already set in the cumulative value of the required air flow rate. The apparatus for performing this function is the critical subtractor 360 .

When controlling the diaphragm valve in this way, the time required for the valve to open or close becomes larger as the required air flow rate becomes smaller or smaller than the set upper limit value (+ DELTA S) or lower limit value (- DELTA S) . This means that the smaller the required air flow, the lower the average air outflow.

That is, the critical-value subtractor 360 is an apparatus for preventing an infinite increase in the cumulative value of required air flow rate, and is a device that not only computes numerical errors such as overflow, And performs a function of eliminating the delay 340 effect.

4 is a timing chart showing an example of valve opening and closing according to the present invention. Referring to FIG. 4, when the required air flow rate is ui, the process of opening and closing the valve is expressed as a function of time. As shown in Fig. 4, when the valve is opened, it can be confirmed that the ratio of the opening time of the valve to the elapsed time is proportional to the required air flow rate ui. This shows that the control method according to the present invention, which proposes a valve opening / closing operation by a predetermined time DELTA T, can control the valve opening / closing amount proportional to the required air flow rate. When the required air flow accumulation value in FIG. 4B is larger than the upper limit value (+ DELTA S) by the selected threshold value or smaller than the lower limit value (- DELTA S) by the predetermined threshold value, as shown in FIG. 4C, The vent valve is activated.

On the other hand, if the driving voltage supplied to the solenoid for controlling the rod / vent valve is lowered, the time required for fully opening and closing the valve may increase. This phenomenon often occurs when the voltage supplied to the control device is not used solely by the solenoid but is used in common with other configurations.

Therefore, unless the valve opening / closing time [Delta] T is adjusted in a state in which the driving voltage supplied to the solenoid is lowered, the amount of air flowing in and out of the valve once is unstable, and the control performance may be greatly deteriorated.

In the present invention, the predetermined period ΔT, that is, the opening / closing time of the rod / vent valve can be adjusted by adjusting the absolute value of the selected threshold value ΔS for more stable displacement control of the diaphragm.

Specifically, the adjusted threshold value (△ S ') is △ S (△ Q / △ Q 0) , where △ S is the threshold, △ Q 0 before adjusting the opening and closing in the absence of a change of the drive voltage Q is the amount of air that goes in and out during the opening and closing time when a change in the driving voltage occurs.

First, ΔT is a function value with respect to the driving voltage (V), and ΔT = g (V). The air flow rate through the valve once the valve is opened is a function value for? T and P (air pressure magnitude), and? Q = f (? T, P). Therefore, it can be confirmed from the above two functions that? Q = h (V, P).

Required air flow

Figure 112015104461297-pat00012
Assuming that a constant u i value is maintained, n times of T time elapses, the voltage is maintained at V 0 , the pneumatic pressure is maintained at P 0 , and if m loads are performed,
Figure 112015104461297-pat00013
.

The equation

Figure 112015104461297-pat00014
And
Figure 112015104461297-pat00015
, And if n is large,
Figure 112015104461297-pat00016
And
Figure 112015104461297-pat00017
. ≪ / RTI > Therefore, the ratio of the number m of valve openings in total n times is the required air flow rate
Figure 112015104461297-pat00018
This fact shows that a controller that performs valve opening and closing operations by a predetermined time T can control the valve opening / closing amount proportionally to the required air flow rate.

However, if the amount of air entering and exiting the valve changes once due to the change in voltage and air pressure

Figure 112015104461297-pat00019
Is not flowing,
Figure 112015104461297-pat00020
.

Therefore, even if the voltage and the air pressure change,

Figure 112015104461297-pat00021
≪ RTI ID = 0.0 >
Figure 112015104461297-pat00022
.

That is, the electronic pneumatic control device according to the present invention adjusts the opening and closing times of the rod and vent valves in accordance with the change of the driving voltage supplied to the rod and vent valves, so that even if the characteristics of the valve opening / The displacement of the diaphragm can be adjusted more stably without changing the control characteristic without changing the control input signal.

Although the present invention has been described with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined in the following claims. It can be understood that

330: PID modulation module 360: critical subtractor
371: load output generating device 372: vent output generating device
390: Rod valve 391: Bent valve
395: Diaphragm valve

Claims (3)

1. An electropneumatic control device for controlling air pressure in a diaphragm by using a load valve and a vent valve connected to a diaphragm,
For calculating a required air flow rate to be supplied to the diaphragm by comparing the output value of the controlled variable controlled by the diaphragm and the set target value for each predetermined period (DELTA T), and for opening / closing the rod valve or the vent valve A PID modulator for generating a control input signal;
The range of the predetermined threshold value? S indicating the required air flow accumulation value as the upper limit value (+ DELTA S) or the lower limit value (- DELTA S) while accumulating the required air flow rate for each of the predetermined periods (DELTA T) The threshold value? S is subtracted or added to the required air flow rate accumulation value to decrease the absolute value of the accumulated value when the load valve or the vent valve is opened for the predetermined period? T, A subtractor;
Wherein when the output value of the critical subtractor is greater than the predetermined upper limit value (+ DELTA S), a control signal for opening the load valve is generated, and when the output value is smaller than the predetermined lower limit value (- DELTA S) A load / vent selector for generating a control signal for the load / vent selector;
When the cumulative air flow rate is greater than the predetermined upper limit value (+ DELTA S), a digital pulse signal having a fixed pulse width selected from the load / vent selector to open the load valve for the predetermined period ([Delta] T) A load output generating device for controlling the load valve;
When the accumulated air flow rate is smaller than the predetermined lower limit value (- DELTA S), a digital pulse signal having a fixed pulse width selected from the load / vent selector and having the vent valve opened for the predetermined period (AT) A vent output generating device for controlling the vent valve;
Vent valve, the opening / closing time of the rod / vent valve is adjusted in response to a change in the driving voltage supplied to the rod / vent valve,
And adjusts the threshold value (? S) to adjust the predetermined period (? T) corresponding to the opening / closing time of the rod / vent valve. delete The method according to claim 1,
The adjusted threshold value [Delta] S '
DELTA S '= DELTA S (DELTA Q / DELTA Q < 0 >),
△ S is the threshold value before the regulation, △ Q 0 is characterized in that the amount of air entering the open and close time if △ Q is air, which is accessible to the opening and closing time when the change in the drive voltage generating When the drive voltage constant And an electronic pneumatic control device.
KR1020150149679A 2015-10-27 2015-10-27 Pneumatic type digital process controller KR101724017B1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100328519B1 (en) * 1999-02-23 2002-03-13 강호일 A digital process controller having a pulse train with a fixed pulse width
KR101230547B1 (en) * 2007-05-08 2013-02-07 주식회사 만도 Apparatus for controlling pulse width modulation and method for controlling thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100328519B1 (en) * 1999-02-23 2002-03-13 강호일 A digital process controller having a pulse train with a fixed pulse width
KR101230547B1 (en) * 2007-05-08 2013-02-07 주식회사 만도 Apparatus for controlling pulse width modulation and method for controlling thereof

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