JPH0418162B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a valve positioner used in a pneumatic control valve.

[Conventional technology]

Conventional general valve positioners apply the deviation between the input signal and the valve displacement amount to the nozzle flapper as a mechanical displacement amount, extract the nozzle back pressure of the nozzle flapper as a pneumatic signal, and then output the pressure using a pilot relay. It is configured to amplify and supply the air motor of the control valve.

[Problem that the invention seeks to solve]

However, with such conventional valve positioners, it is difficult to respond at high speed when the deviation between the input signal and the amount of displacement of the valve is large. In particular, when the capacity of the air motor is large, it is necessary to separately add a booster relay to the air circuit to amplify the capacity of the air pressure signal to support high-speed response.

[Means for solving problems]

In order to solve these problems, the present invention inputs a valve drive signal that indicates the deviation between the input signal and the opening degree of the pneumatic control valve, and makes sure that the absolute value of this valve drive signal is a predetermined value. A pulse width modulation means outputs a pulse width modulated signal when δ1 or less, and the output signal of the pulse width modulation means is converted into a pulse width modulated air pressure signal, and this air pressure signal is used to open the valve of the pneumatic control valve. The three-way switching valve input to the drive pressure chamber to displace the degree and the value of the valve drive signal δ1
A large capacity air supply valve that connects the driving pressure chamber with the air pressure source when the value is greater than or equal to a larger value δ2, and a large capacity air supply valve that connects the driving pressure chamber to the atmosphere when the value of the valve driving signal is less than or equal to a predetermined value −δ2 that is smaller than −δ1. This device is provided with a large-capacity exhaust valve to be communicated with, and means for setting the absolute value of δ2 to be small when the opening degree of the valve is large, and large when the opening degree of the valve is small.

[Effect]

If there is a large deviation (absolute value δ2) between the input signal and the valve opening, the drive pressure chamber will be directly connected to an air pressure source or the atmosphere, causing its pressure to change rapidly and increase the valve opening. change. When the opening degree is small, that is, high load, and when the opening degree is large, that is, low load, there is a difference in response characteristics to the same input signal change width, but according to the present invention, the pneumatic source or By changing the deviation (predetermined value) communicated with the atmosphere according to the valve opening degree, it is smoothly converged to the desired value regardless of the load.

〔Example〕

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

The pneumatic control valve 10 includes a driving pressure chamber 101 and a valve 102, and the opening and closing of the valve 102 is controlled by air pressure supplied to the driving pressure chamber 101.

An air pipe 12 is connected to the drive pressure chamber 101, and the other end of this air pipe 12 is connected to a three-way switching valve 14,
It is connected to a large capacity air supply valve 16 and a large capacity exhaust valve 18.

The three-way switching valve 14 has a pressure Ps in addition to the air pipe 12.
Air pipe 20 communicating with a source of air pressure and pressure P ₀
It is connected to an air pipe 22 that communicates with the atmosphere. The connection between the air pipe 20 and the air pipe 12 and the connection between the air pipe 22 and the air pipe 12 are then switched in response to a signal from the pulse width modulator 24.

The large-capacity air supply valve 16 is an on/off switching valve that connects and disconnects the air pipe 20 and the air pipe 12 based on a signal from the comparator 26. Pipe 22 and air pipe 1
This is an on/off switching valve that connects and connects the

The valve lift detector 30 detects the position of the valve 102 and outputs a voltage value V1 according to the position, and can be configured with a rotary encoder, a potentiometer, or the like.

The input module 32 converts an input signal of 4 to 20 mA inputted from the input terminal 34 into a voltage value V2, and this voltage value V2 is compared with the voltage value V1 from the valve lift detector 30 in a comparator 36. be done.

The deviation ε between the voltage value V1 and the voltage value V2 represents the difference between the valve position indicated by the input signal and the actual valve position, and the pulse width modulator 24, comparator 26 and comparator 28 are used as the valve drive signal. is input.

As shown in the characteristic diagram of FIG. 2A, the pulse width modulator 24 pulses the valve drive signal ε only when the input valve drive signal ε satisfies −δ1≦ε≦δ1 (1). Modulate the width. The duty ratio when ε=-δ1 is set to zero, and the duty ratio when ε=δ1 is set to "1", and the relationship between ε and the duty ratio when equation (1) is satisfied is linear.

The waveform diagram in FIG. 3 shows the output waveform of the pulse width modulator 24 when ε=ε1, that is, when the duty ratio is "0.7", and the waveform of the pulse width modulator 24 is shown when the repetition period T is
70% is at "H" level and the remaining 30% is at "L" level.

When the valve drive signal ε satisfies ε<-δ1...(2), the output of the pulse width modulator 24 is 2
When the value signal becomes "L" level and the valve drive signal ε satisfies ε>δ1...(3), the output of the pulse width modulator 24 is 2.
The value signal becomes "H" level.

Note that the three-way switching valve 14 has a pulse width modulator 24.
When the signal from the air pipe 22 is at “H” level,
The opening of the air pipe 20 is closed to connect the air pipe 20 and the air pipe 12, and when the level is "L", the opening of the air pipe 20 is closed to connect the air pipe 22 and the air pipe 12.

As shown in the characteristic diagram of FIG. 2B, the comparator 26 outputs a binary output signal "H" when the valve drive signal ε satisfies ε≧δ2 (however, δ2>δ1)...(4) When ε<δ2 (5) is satisfied, the binary output signal becomes “L” level.

When the signal from the comparator 26 is at "H" level, the large-capacity air supply valve 16 opens the opening of the air pipe 20 and connects the air pipe 20 and the air pipe 12. When the signal from the comparator 26 is at the "L" level, the opening of the air pipe 20 is closed and the connection between the air pipe 20 and the air pipe 12 is disconnected. .

Furthermore, as shown in the characteristic diagram of FIG. When the signal becomes "H" level and satisfies ε>-δ2 (7), the binary output signal becomes "L" level.

In the large-capacity exhaust valve 18, when the signal from the comparator 28 is at "H" level, the opening of the air pipe 22 is opened and the air pipe 22 and the air pipe 12 are connected. Room 101 and atmosphere (P ₀ )
When the signal from the comparator 28 is at "L" level, the opening of the air pipe 22 is closed and the connection between the air pipe 22 and the air pipe 12 is disconnected.

Next, the operation of this embodiment will be explained.

If the value of the valve drive signal ε from the comparator 36 is, for example, ε1 (0<ε1<δ1) as shown in FIG. 2A, the pulse width modulator 24 simultaneously performs the pulse width modulation operation. Comparators 26 and 2
Both outputs of 8 are at "L" level.

That is, the large capacity air supply valve 16 and the large capacity exhaust valve 18 are both in a non-communicating state, and the driving pressure chamber 101 is in communication with the air pressure source (Ps) and the atmosphere (P ₀ ) only through the three-way switching valve 14. be done.

Since the three-way switching valve 14 is currently driven by a pulse width modulation signal with a duty ratio of 0.7, the air pipe 12 communicating with the drive pressure chamber 101 is connected to the air pipe 20, that is, the air pressure source (Ps), for 70% of the repetition period T. 30% of the time is communicated with the air pipe 22, ie, the atmosphere (P ₀ ).

Therefore, air from the air pressure source (Ps) is gradually supplied to the driving pressure chamber 101, and the valve 102 is gradually displaced accordingly.

Assuming that the signal input to the input terminal 34 is constant, the valve drive signal ε gradually approaches zero due to the displacement of the valve 102, and when ε=0, the output signal of the pulse width modulator 24 changes. The duty ratio of is 0.5.

Since the pneumatic control valve 10 is adjusted so that the displacement of the valve 102 is stopped by the supplied air pressure at this time, the driving of the valve 102 is stopped unless the input signal changes thereafter.

Next, consider a case where the signal input to the input terminal 34 increases rapidly.

If the valve drive signal ε becomes [ε≧δ2] due to an increase in the input signal level, the comparator 28 still outputs an “L” level signal to maintain the large capacity exhaust valve 18 in a non-communicating state. However, comparator 2
The output of 6 becomes “H” level, and the large capacity air supply valve 1
6 into communication state.

Further, the pulse width modulator 24 stops the pulse width modulation operation and outputs an "H" level signal, thereby causing the three-way switching valve 14 to constantly communicate the air pipe 12 and the air pipe 20.

Therefore, the driving pressure chamber 101 is the three-way switching valve 1
The pressure supplied to the driving pressure chamber 101 rapidly increases, and the pressure supplied to the drive pressure chamber 101 suddenly increases.
02 is greatly displaced. In other words, it responds quickly to a large increase in input.

When the value of ε becomes smaller [-δ1≦ε≦δ1] due to the displacement of the valve 102, the operation returns to the pulse width modulation described above.

Conversely, when the signal input to the input terminal 34 suddenly decreases, that is, when [ε≦−δ2], the output of the pulse width modulator 24 and the comparator 2
The output of comparator 6 becomes "L" level, and the output of comparator 28 becomes "H" level. As a result, the three-way switching valve 1
4 brings the air pipe 12 and the air pipe 22 into communication, puts the large-capacity air supply valve 16 into a non-communicating state, and puts the large-capacity exhaust valve 18 into a communicating state.

Therefore, the driving pressure chamber 101 is the three-way switching valve 1
4 and the large capacity exhaust valve 18, the drive pressure chamber ₁
The pressure supplied to 01 suddenly drops, and the valve 102 is largely displaced in the opposite direction to when the value of ε increases.

As the value of ε increases due to the displacement of the valve 102 [-δ1≦ε≦δ1], the pulse width modulation operation is returned to, as in the above case.

However, even if the input signal changes in the same way, communication with the air pressure source or the atmosphere depends on the load level at that time, that is, the pressure in the drive pressure chamber 101 before the above change occurs. There will be a difference in response characteristics when For example, when the load level is high (about 60 to 80%), it will respond normally to a 20% increase or decrease in the same input signal, but when the load level is low, about 0 to 20%, it will respond normally. It sometimes occurs that the response has a tendency to overshoot.
The reason for this is that in this embodiment, the large-capacity intake valve 16 or the large-capacity exhaust valve 18 opens due to a change in the input signal and closes when the deviation reaches δ2. Due to dead time and response time,
It takes a certain amount of time for the valve to actually close completely after the electrical signal is sent, and this is thought to be due to the fact that the flow rate is large, especially when the load level is low, so the valve may overshoot during this time. .

This will be explained in more detail using figures. Fourth
Figure a shows that the load level is 0% (indicated by A in the figure).
In the case of 75% (indicated by B in the figure), the change in pressure in the drive pressure chamber 101 corresponding to the stem position of the valve 102 with respect to an increase in the input signal by 25% is shown in Figure b. Large capacity air supply valve 16
This figure shows the output of the comparator 26 that drives the . Assuming that δ2 is 5%, if the input signal increases by 25% at _t0 as shown by the dashed line in the figure, the deviation ε becomes 25% at that point and the large capacity air supply valve 26 opens. Then, the valve lift detector 30 detects ε=
When 5% is detected, the large-capacity air supply valve 26 closes, and then the three-way switching valve 14 driven by the pulse width modulation signal converges to the desired value. However, as shown by the broken line in the figure, the pressure increases exponentially toward Ps (1.4Kg/cm ² in this example), so the differential coefficient of pressure at time t ₁ , in other words, the flow rate is , differs depending on the load level; it is large when the load level is low, and small when the load level is large. Furthermore, since the response of the air system switch is slower than that of the electric system, the large capacity air supply valve 16 actually closes later than _t1 . Therefore, when the flow rate is large, that is, when the load is low, the flow rate exceeds the desired value. This can be resolved by setting a larger value for δ2, but doing so will result in overdamp when the load is high. Although the case where the input signal rapidly decreases has been described above, the same applies to the case where the input signal suddenly decreases.

Therefore, in order to avoid such a difference in response depending on the load level, in the present invention, the value of δ2 is changed depending on the load level. This can be realized very easily, for example, by using a microcomputer equipped with a well-known processor unit. For example, FIG. 5 shows an example of a processing program executed by the processor unit when the comparators 26, 28 and pulse width modulator 24 in FIG. 1 are constructed using a microcomputer. In the figure, the processor unit takes in the AD-converted input signal and the output of the valve lift detector 30, and determines the load level x (step 101). Next, the deviation ε is calculated, and the sixth
The corresponding δ2 _x is determined from data relating the load level and the value of δ2 as shown in the figure (δ2=1/x in the illustrated example) (step 102). Then, check the magnitude relationship between the absolute value of ε and δ2 _x (step
103), if the former is less than the latter, a predetermined pulse width modulation signal is given to operate the three-way switching valve 14 (step 104), and if the former is greater than the latter, the large capacity air supply valve 16 or the large The capacity exhaust valve 18 is operated (step 105). The above processes and programs are repeatedly executed at predetermined intervals.

In the above-described embodiment, the relationship between the load level and the value of δ2 is given in advance as fixed data, but if it is acquired by learning at the initial stage of operation, more desirable control suitable for each individual device can be performed.

FIG. 7 is a block diagram showing another embodiment of the present invention. In this embodiment, a means for sealing the pressure in the drive pressure chamber when the deviation is close to zero is added to the valve positioner shown in FIG.

That is, although a nozzle flapper and a pilot relay are used in a conventional valve positioner, the nozzle flapper and pilot relay consume air even in an equilibrium state. Specifically, a valve positioner using a semi-bleed type pilot relay or a bleed type pilot relay has a pressure of 5 to 15 Nl per nozzle and pilot relay.
There is mim air consumption.

Non-bleed type pilot relays have been available as pilot relays that minimize air consumption in an equilibrium state, but the air consumption is not zero, and air consumption at the nozzle is unavoidable. Moreover, non-bleed type pilot relays have the disadvantage of poor response.

In view of these circumstances, the present embodiment has the following features: as described above, even if the deviation between the input signal and the displacement amount of the valve is large, the control valve can be made to respond at high speed without using a booster relay; The present invention provides a valve positioner with zero air consumption in an equilibrium state.

In FIG. 7, the same or corresponding parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

The comparator 40, as shown in the characteristic diagram of FIG.
The “L” level is output only when the input valve drive signal ε satisfies −δ0<ε<δ0 (8) (however, −δ1<−δ0<0, 0<δ0<δ1), and other In this case, "H" level is output.

The output of comparator 40 is provided to on/off switching valve 42 and gate circuit 44.

The on/off switching valve 42 is provided between an air pipe 121 that communicates with the three-way switching valve 14, the large-capacity air supply valve 16, and the large-capacity exhaust valve 18, and an air pipe 122 that communicates with the drive pressure chamber 101. When the output of the comparator 40 is at the "L" level, it is in a non-communicating state to seal the pressure inside the drive pressure chamber 101, and when the output of the comparator 40 is at the "H" level, it is in the communicating state.

The gate circuit 44 is provided between the pulse width modulator 24 and the signal input terminal of the three-way switching valve 14, and when the output of the comparator 40 is at the "L" level, the output signal is at the "L" level, and the output signal from the comparator 40 is at the "L" level. When the output of the pulse width modulator 24 is at the "H" level, the output signal of the pulse width modulator 24 is output as is.

Therefore, as shown in FIG. 9, the output of the gate circuit 44 is "L" when [ε<-δ1, -δ0<ε<δ0].
When [ε>δ1], it becomes an "H" level, and when [-δ1≦ε≦-δ0, δ0≦ε≦δ1], it becomes a pulse width modulation operation.

Next, the operation of this embodiment will be explained.

When the value of the valve drive signal ε satisfies ε<-δ0, δ0<ε, the operation is the same as that of the above-mentioned embodiment, so a description thereof will be omitted.

Therefore, the value of the valve drive signal ε is −δ0＜ε＜δ0 Let me explain what happens when this happens.

When the value of the valve drive signal ε falls within the range [-δ0<ε<δ0], the three-way switching valve 14 stops the pulse width modulation operation and closes the air pipe 20. On the other hand, the large capacity air supply valve 16 is in a non-communicating state because the value of the valve drive signal ε is [ε<δ2]. Therefore,
The air supply path from the air pressure source (Ps) is completely cut off, and air consumption in this state is zero.

On the other hand, the on/off switching valve 42 becomes disconnected when the value of the valve drive signal ε falls within the range of -δ0<ε<δ0, so the air pipe 121 is connected via the three-way switching valve 14. Although it communicates with the atmosphere (P ₀ ), the air within the driving pressure chamber 101 is not exhausted, and the position of the valve 102 is maintained constant.

Note that if the value of the valve drive signal ε changes due to a new signal input and becomes outside the range of [−δ0<ε<δ0], this sealed state is released.

In this embodiment as well, by variably setting δ2 as described above, good response characteristics can be obtained regardless of the load level.

〔Effect of the invention〕

As explained above, according to the valve positioner of the present invention, the valve drive signal indicating the deviation between the input signal and the valve opening is pulse width modulated and then converted into a pneumatic pressure signal, and this pneumatic pressure signal is used to control the pneumatic control valve. At the same time, when the absolute value of the valve drive signal is less than δ1, pulse width modulation is performed, and when the absolute value of the valve drive signal is greater than δ2, which is greater than δ1, the drive pressure chamber of the pneumatic control valve is changed to a pneumatic pressure source. Alternatively, since the control valve is communicated with the atmosphere, even if the deviation between the input signal and the position of the valve is large, the control valve can be made to respond at high speed without using a booster relay. That is, pulse width modulation is performed in a range where the valve drive signal is small, and when the valve drive signal is large, air is directly taken in and out without modulation, allowing for highly accurate and high speed control. Furthermore, by variably setting the predetermined value in accordance with the opening degree of the valve, it is possible to always obtain optimal response characteristics regardless of the load level.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the valve positioner of the present invention, FIG. 2 is a characteristic diagram of the pulse width modulator and comparator of the embodiment, FIG. 3 is an output waveform diagram of the pulse width modulator, and FIG. Figure 4 is a diagram for explaining the difference in response characteristics depending on the load level, and Figure 5 is a diagram of the processing program in the processor unit when the comparators 26, 28 and the pulse width modulator 24 are configured using a microcomputer. A flowchart showing an example, Figure 6 shows the load level and δ2
7 is a block diagram showing another embodiment of the valve positioner of the present invention, FIG. 8 is a characteristic diagram of a comparator, and FIG. 9 is a characteristic diagram of a gate circuit. . 10...Pneumatic control valve, 101...Driving pressure chamber, 102...Valve, 12, 121, 122,
20, 22...Air pipe, 14...Three-way switching valve, 1
6...Large capacity air supply valve, 18...Large capacity exhaust valve, 2
4... Pulse width modulator, 26, 28... Comparator,
30... Valve lift detector.

Claims (1)

[Claims] 1. A valve drive signal indicating the deviation between the input signal and the opening degree of the pneumatic control valve is input, and when the absolute value of this valve drive signal is less than or equal to a predetermined value δ1, pulse width modulation is performed. pulse width modulation means for outputting a signal that is pulse width modulated; a three-way switching valve that inputs input to the drive pressure chamber; a large-capacity air supply valve that communicates the drive pressure chamber with an air pressure source when the value of the valve drive signal is equal to or greater than a predetermined value δ2 larger than δ1; and the valve drive signal. a large-capacity exhaust valve that communicates the driving pressure chamber with the atmosphere when the value of is equal to or less than a predetermined value −δ2 smaller than −δ1; and a large-capacity exhaust valve that communicates the driving pressure chamber with the atmosphere when the value of 1. A valve positioner comprising a variable setting means for setting a small opening degree to a large value when the opening degree is small.