JPH08263103A - Method and device for stable control over operation terminal using pulse/air pressure transducer - Google Patents

Abstract

PURPOSE: To provide the method and device for stable control over the operation terminal which can stably control the operation terminal in a process stable area and uses the pulse/air pressure transducer having excellent follow-up characteristics at process quantity variation time. CONSTITUTION: As for the stable control method for the operation terminal which uses the pulse/air pressure transducer controlling the operation terminal by outputting control pulses to the pulse/air pressure transducer 16 so as to control the process quantity of a line 10 to a set value by connecting the operation terminal 12 that operates with air pressure to control air pressure to the line 10 where process fluid flows and the pulse/air pressure transducer 16 controlling the air pressure according to a pulse signal to the operation terminal 12, an increase and a decrease of the control pulses outputted to the pulse/air pressure transducer 16 are monitored for a certain time and when the increase and decrease are repeated, the pulses outputted to the pulse/air pressure transducer 16 are suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling a pneumatically operated operating end of a control valve or the like for controlling process amounts of various fluids, and more particularly to operating the operating end with a pulse / pneumatic pressure converter. The present invention relates to a stable control method and device for an operating end using a pulse / pneumatic pressure converter for control.

[0002]

2. Description of the Related Art An operating end such as a control valve for controlling a process amount such as a flow rate, a pressure or a liquid level is connected to a line through which a fluid to be controlled flows, and a valve opening at the operating end is adjusted to adjust the fluid flow. The process amount (flow rate, etc.) is controlled.

This operating end detects the flow rate and pressure of the fluid in the line, for example, and performs process control so that the detected value becomes a set value.

Conventionally, a current / pneumatic signal converter has been used as a controller for operating the operating end, and the operating end has been controlled by analog control. However, it is easy to deal with the converter and the controller. Pulse / pneumatic transducers that convert pulses to pneumatic signals are becoming more popular.

A controller using this pulse / pneumatic pressure converter outputs a pulse to the operating end according to the "increase" or "decrease" pulse signal output from the controller each time one pulse is sent to the pulse air pressure converter. A corresponding air pressure signal is output to gradually open or close the valve opening of the operating end so as to adjust the opening of the operating end so that the process amount maintains the set value. This pulse / pneumatic pressure converter has an advantage that the state of the operating end can be maintained even if an abnormality occurs in the equipment of the control loop.

[0006]

By the way, in the control of the operating end by this controller, the gain is set so as to follow the movement of the controlled object, and the followability is good in the transition period when the process control changes. Control is possible, but when the process amount reaches the stable range, the operating end is opened and closed more than necessary,
Hunting occurs when the operating end is small. This movement is generated from the minimum pulse signal output from the controller, the movement of the converter, and the resolution of the operating end, but it may shorten the life of the operating end more than necessary.

To solve this problem, it is possible to reduce the movement by adjusting the gain of the controller.
Then, on the contrary, there is a problem that the controllability when the process amount changes becomes poor. That is, if the opening / closing degree of the valve per pulse is reduced, the control amount and the process amount can be matched in the stable region, but since the gain becomes low, there is a problem in control followability, and conversely, If the gain is increased and the valve opening degree per pulse is increased, the followability at the time of change is good but stable control is lacking. Therefore, in the related art, since gain adjustment is performed in consideration of these, there is a problem that control that satisfies both controls is substantially difficult.

Therefore, an object of the present invention is to solve the above-mentioned problems and to stabilize the operating end by using a pulse / pneumatic pressure converter capable of stably controlling the operating end in the process stability region and having good followability when the process amount changes. It is to provide a control method and apparatus.

[0009]

In order to achieve the above-mentioned object, the invention of claim 1 connects an operation end for operating a pneumatic pressure to adjust a process amount to a line through which a process fluid flows, and the operation end is connected. , A pulse / pneumatic pressure converter for controlling the air pressure according to the pulse signal is connected, and a pulse for controlling the operating end by outputting a control pulse to the pulse / pneumatic pressure converter to set the process amount of the line to a set value. / In a stable control method of the operating end using a pneumatic pressure converter, the increase / decrease of the control pulse output to the pulse / pneumatic pressure converter is monitored for a certain period of time, and when the increase / decrease is repeated, it is output to the pulse / pneumatic pressure converter It is a stable control method of an operating end using a pulse / pneumatic pressure converter, which is characterized by suppressing pulses.

According to a second aspect of the present invention, a pulse / pneumatic pressure converter is connected to a line through which a process fluid flows and which is connected to an operating end for operating by air pressure to adjust a process amount, and which controls the air pressure according to a pulse signal. And a stable control device for the operating end using a pulse / pneumatic pressure converter for adjusting the operating end by outputting a control pulse to the pulse / pneumatic pressure converter to set the process amount of the line to a set value. A normal control system that outputs an increase / decrease pulse to the pulse / pneumatic pressure converter based on the value and the process variable of the line; a stable control system that suppresses the output pulse when the set value and the process variable are in substantially the same stable region; An operation using a pulse / pneumatic pressure converter characterized in that it is provided with a switching control means for monitoring the increase / decrease for a certain period of time and switching between the normal control system and the stable control system according to the increase / decrease A stable control system.

[0011]

According to the above construction, when the process displacement amount is large, normal control is performed, and when the process displacement is small with respect to the set value and the stable region is reached, the output pulse to the pulse / pneumatic pressure converter is suppressed. As a result, hunting of the process amount can be suppressed, and thus unnecessary opening / closing movement of the operating end can be eliminated and its life can be extended.

[0012]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an outline of an apparatus and a logic for carrying out a stable control method of an operating end using a pulse / pneumatic pressure converter of the present invention.
Is a line through which various process fluids flow, and an operating end (control valve or the like) 12 that is pneumatically operated, such as a control valve, is connected to the line 10. A detector 14 for detecting the process amount of the line 10 is connected to the upstream side (or the downstream side) of the operating end 12.

The operating end 12 has a pulse / pneumatic pressure converter 16
The process amount of the line 10 is controlled by variably adjusting the valve opening with the air pressure from. The pulse / pneumatic pressure converter 16 receives the positive and negative (“increase” or “decrease”) pulse signals supplied from the controller 18 from the operating end 1.
2 outputs an air pressure signal corresponding to the pulse, and controls the operation end 12 so as to increase or decrease the air pressure at the operation end 12 according to the pulse to reach the set valve opening. Further, the pulse / pneumatic pressure converter 16 has a feature that the state of the operating end 12 can be maintained even if an abnormality occurs in a device on the control loop.

The detector 14 detects the flow rate of the fluid in the line 10,
A process amount such as pressure and liquid level (static pressure) is detected, and this is output to the controller 18 as a process variable PV.

A set value SV is input to the controller 18, and the pulse / pneumatic pressure converter 16 is controlled so that the process amount becomes the set value SV from the set value SV and the process variable PV.
A control pulse is output to.

The controller 18 calculates the set value SV and the process variable PV to obtain a displacement, and an adder 20.
Control switch 22 for switching control, and the control switch 2
2, a normal control system 24 connected to one side, a stable control system 26 connected to the other side, and a control amount ((PV-SV) N) from both control systems 24, 26 to generate a control pulse command. And a control pulse command from the control calculator 28 for increasing / decreasing 30 or 32 pulses.
The pulse generator 34 outputs to the air pressure converter 16, and further, the increase / decrease pulses 30 and 32 are input, and the switching control means 36 switches the control switch 22 based on the pulse. .

The operating end 12 is, for example, 0.2 to 1.0 kg.
Operated from full closed to full open with an air pressure in the range of / cm ² , and the pulse / pneumatic pressure converter 16 sets the number of pulses corresponding to the above-mentioned pressure range at the resolution of the operating end 12 and one pulse is input. Each time, the air pressure to the operating end 12 can be varied substantially continuously within the range of 0.2 to 1.0 kg / cm ² .

The normal control system 24 of the controller 18 determines P, P based on the set value SV and the displacement (PV-SV) of the process variable PV.
Control amount ((PV-SV) N) by PI, PD, PID control, etc.
Is output to the control calculator 28. In this case, the gain in the normal control system 24 is set so that a desired number of pulses are output at an appropriate pulse interval with respect to the control amount ((PV-SV) N) and can follow the change.

The stable control system 26 is in the stable control region where the set value SV and the process variable PV are substantially the same, and when the process variable is large in the above-mentioned control amount per pulse, Particularly when hunting around the set value SV in the stable region, the output of the pulse is suppressed at intervals such that the gain is lower than the gain of the normal control system 24.

That is, for example, assuming that the normal control system 24 controls the relationship between the displacement (PV-SV) and the controlled variable ((PV-SV) N) in a proportional relationship as shown in the figure, the controlled variable ( (PV-SV)
When N) is in the stable range near 0, a dead zone is set for the displacement (PV-SV) and the control amount ((PV-SV) is set in this gap area t as shown by the dotted line in the figure. When there is N), the control amount is the control amount in the stable region (0)
It outputs to 8 as a suppression signal.

The gap region t is set to be equal to or longer than the minimum pulse interval in the normal control system 24, and for example, the normal control system 24 is used.
Then, even if one or two pulses are output in the gap region t, the pulse is suppressed from being output.

The switching control means 36 monitors the pulse output within a fixed time by using the pulse of increase 30 or decrease 32 from the pulse generator 34 as a trigger, and (1) the increase / decrease pulse is repeated 5 times, for example. If the control switch 22 is switched to the switch 2, (2) If the increase or decrease is continuously output, the control switch 22 is switched to the switch 1, (3)
In the states other than the above (1) and (2), the control switch 22 is controlled so that the switch continues the previous state.

Next, the operation of the embodiment will be described.

First, the set value SV is sequentially changed according to various controls, and accordingly, the controller 18 operates the pulse / pneumatic pressure converter 16 so that the process amount PV matches the set value SV. Control twelve.

First, at the start of control, the control switch 22 is set to the switch 1, and the normal control system is controlled in that state.
When the process variable PV is small and stable, the control switch 22 is switched to the switch 2 to control the stable control system 26, and when the process variable PV fluctuates, the control switch 22 is switched to the switch 1 and the normal control system. It is returned to 24 and controlled.

Switching of the switches 1 and 2 of the control switching device 22 is performed by the switching control means 36, and the switching control means 36 monitors the increase / decrease pulses 30 and 32 of the pulse generator 34 so that either control system The control switch 22 is controlled to switch to 24 and 26.

The switching control of the switching control means 36 is output from the pulse generator 34 when the set value SV fluctuates or when the normal control system 34 has a large difference in the process variable PV with respect to the set value SV. Pay attention to the fact that pulses of increasing 30 or decreasing 32 are continuously generated, and the set value S
In the case of the stable control system 26 in which the difference between V and the process variable is close to zero, the number of pulses output from the pulse generator 34 increases.
Focusing on the fact that 0 and subtraction 32 are alternately repeated, the normal control system 24 or the stable control system 26 is switched.

This control operation will be described in more detail with reference to the timing chart of FIG.

FIG. 2A shows the change over time of the process variable PV when the set value SV is changed over time.
(B) shows the output state of the increase / decrease pulse at that time.

In FIG. 2A, the set value SV temporarily drops (change region R1), then stabilizes at the lowered value (stable region R2), and rises and falls from the stable value (variation range R3). It is assumed that the set value changes the SV.

In this case, first, in the change region R1, as shown in FIG.
As shown in (b), the deceleration pulse is continuously output and controlled so as to close the opening degree of the operating end 12, and accordingly the process variable PV is lowered. Next, when shifting to the stable region R2, the output pulse of the controller 18 outputs an increasing or decreasing pulse so as to maintain the set value SV1 of the stable region R1. At this time, if the increase / decrease pulse is repeated 5 times, the switching control means 36 switches the control switching device 22 to the switch 2
To the stable control system 26. By switching to the stable control, the process variable that was hunting around the set value SV2 is stabilized by suppressing the pulse output.

When shifting from the stable region R1 to the variable region R3, the control amount ((PV-SV) N) in the stable control system 26 described in FIG. 1 is the control amount in the gap region t which is the dead zone. Therefore, the increase pulse is continuously output similarly to the normal control system 24, and in response to this, the switching control means 36
However, the control switch 22 is switched to the switch 1 side and switched to the normal control system 24 to control the process amount in accordance with the fluctuation of the set value.

[0034]

In summary, according to the present invention, passage control is performed when the process displacement amount is large, and when the process displacement is small with respect to the set value and the stable region is reached,
By suppressing the output pulse to the pulse / pneumatic pressure converter, it is possible to suppress the hunting of the process amount, thereby eliminating unnecessary opening and closing of the operating end and extending its life.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a control operation in the present invention.

[Explanation of symbols]

 10 lines 12 operating end 16 pulse / pneumatic pressure converter 24 normal control system 26 stable control system 36 switching control means

Claims (2)

[Claims] 1. A pulse / pneumatic pressure converter for connecting an operating end 12 for operating a pneumatic pressure to adjust a process amount to a line 10 through which a process fluid flows, and controlling the air pressure at the operating end 12 according to a pulse signal. In a stable control method for an operating end using a pulse / pneumatic converter, which is connected to 16 and outputs a control pulse to the pulse / pneumatic converter 16 so as to set the process amount of the line to a set value. The pulse / pneumatic pressure converter is configured so that the increase / decrease of the control pulse output to the pulse / pneumatic pressure converter is monitored for a certain period of time, and when the increase / decrease is repeated, the pulse output to the pulse / pneumatic pressure converter is suppressed. A stable control method for the operating end using a pneumatic converter. 2. A line 10 through which a process fluid flows, an operating end 12 which is operated by air pressure to adjust the process amount is connected, and a pulse / pneumatic pressure converter 16 which controls the air pressure according to a pulse signal is connected to the operating end. However, in the stable control device for the operating end using the pulse / pneumatic pressure converter, which outputs a control pulse to the pulse / pneumatic pressure converter to adjust the operating end so as to set the process amount of the line to the set value, A normal control system 24 that outputs an increase / decrease pulse to the pulse / pneumatic pressure converter based on the process variable of the line, a stable control system 26 that suppresses the output pulse when the set value and the process variable are in substantially the same stable region, Monitor the increase and decrease for a certain time,
Pulse / characterized by comprising a switching control means 36 for switching between the normal control system and the stable control system according to the increase / decrease.
A stable control device for the operating end using a pneumatic converter.