JPS6220902A - Valve positioner - Google Patents

Abstract

PURPOSE:To secure an optimum responsive characteristic all the time, by connecting a valve driving pressure chamber directly to a pneumatic source and the atmosphere when the absolute value of deviation is larger than the specified value, and making the said specified value variable according to the size of valve opening. CONSTITUTION:A large capacity feed valve 16 and a large capacity exhaust valve 18 both are connected to a driving pressure chamber 101 of a pneumatic control valve 19, while a three-way selector valve 14 to be driven by pulse width modulation is connected to the chamber as well, and when absolute value of deviation between an input signal and a valve displacement of the pneumatic control valve 10 is larger than the specified value, the driving pressure chamber 101 is directly connected to a pneumatic source and the atmosphere, and this specified value is variably set according to the extent of valve opening. With this constitution, it is smoothly convergeable to the desired value, no matter what the load may be, so that an optimum responsive characteristic is securable all the time, not resting on a load level.

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 7 bumper as a mechanical displacement amount, and extract the nozzle back pressure of this nozzle and 7 bumper as a pneumatic signal. , the pressure is amplified by a pilot relay and is supplied to 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 converts the valve drive signal into a pneumatic pressure signal after pulse width modulating the deviation between the input signal and the opening degree of the valve, and drives the valve with this pneumatic pressure signal. In addition to the means, means is provided for communicating the drive pressure chamber of the valve with an air pressure source or the atmosphere when the absolute value of the deviation indicated by the valve drive signal is larger than a predetermined value by υ, and the predetermined value is set to the valve opening degree. It is provided with means for setting the value to be large when it is small and to be small when it is large.

[Effect]

If there is a large deviation (absolute value) between the input signal and the valve opening, the driving pressure chamber will be directly connected to an air pressure source or the atmosphere, and the pressure will change rapidly, causing the valve opening to change. Make a big change. When the opening degree is small, when the claw is under high load, and when the opening degree is large.

There is a difference in the response characteristics to the change width of the same input signal depending on the case where the load is low, but according to the present invention, the air pressure @
Alternatively, 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 driving pressure chamber 101, and the other end of this air pipe 12 is connected to a three-way switching valve 14. Large capacity air supply valve 1
6 and a large capacity exhaust valve 18.

The three-way switching valve 14 is connected, in addition to the air line 12, to an air line 20 communicating with an air pressure source at a pressure P1 and an air line 22 communicating with the atmosphere at a pressure PG. Then, 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 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. This is an on/off switching valve that connects and disconnects the air pipe 22 and air pipe 12 based on a signal.

The valve lift detector 30 detects the position of the valve 102 and outputs a voltage value Vl according to the position 1, and can be configured with a rotary encoder, a potentiometer, or the like.

The input module 32 receives 4 inputs from the input terminal 34.
It converts an input signal of ~20 mA into a voltage value v2, and this voltage value v2 is compared with the voltage value v1 from the valve lift detector 30 in the comparator 36.

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 is used as a valve drive signal by the pulse width modulator 24. Input to comparator 26 and comparator 28.

As shown in the characteristic diagram of FIG.
-@---The valve drive signal e is pulse width modulated only when (1) is satisfied. 1=-δ1
The duty ratio when C; δl is set to 0, and the duty ratio when C; δl is set to 1, and the relationship between 8 and the duty ratio when formula (1) is satisfied is linear.

The waveform diagram in FIG. 3 shows the output waveform of the pulse width modulator 24 when 1=εl, that is, when the duty ratio is rO,7J, and the repetition period TO70 is "H".
The remaining 30% is at "L" level.

Valve drive signal 8 is ε<-δl...(2)
When the output of the pulse width modulator 24 satisfies the "L" level in the binary signal, the valve drive signal C is I>δ1
・ ・ ・ ・ ・ (When 3 is satisfied, the output of the pulse width modulator 24 becomes the "H" level in the binary signal.

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

As shown in the characteristic diagram of the second figure, the comparator 26 is configured such that the valve drive signal C is C≧δ2 (where δ2>δ1) (4
), the binary output value becomes “H” level, e〈δ2...(5
), the binary output value 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.
0 and the air pipe 12 are connected, the air pressure source (P,) and the drive pressure chamber 101 of the pneumatic control valve 10 are connected, and the comparator 2
When the signal from 6 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 severed.

Furthermore, as shown in the characteristic diagram of FIG.
), the binary output value becomes “H” level9, e〉−δ2 (7)
When this is satisfied, the binary output value becomes 'L' level.

In the large capacity exhaust valve 18, when the signal from the comparator 28 is 1H'', the opening of the air pipe 22 is opened and the air pipe 22 and the air pipe 12 are connected, and the driving pressure of the pneumatic control valve 10 is The chamber 101 and the atmosphere (Pa) communicate with each other, and the comparator 28
When the signal from the air tube is at the "'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 severed.

Next, the operation of this embodiment will be explained.

If the valve drive signal IF) value from the comparator 36 is, for example, the second
If it is 51 (0 (11 (δ1)) as shown in FIG. Become.

That is, both the large-capacity air supply valve 16 and the large-capacity exhaust valve 18 are out of communication, and the drive pressure chamber 101 is connected to the air pressure source (P-) and the atmosphere (P.) only by the three-way switching valve 14. communicated.

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

Therefore, air from the air pressure source (Pl) is gradually supplied to the drive 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 C gradually approaches zero due to the displacement of the valve 102, and when g = Q, the output signal of the pulse width modulator 24 changes. The utility ratio will be 0.5.

The pneumatic control valve 10 adjusts the valve 1 at the supplied air pressure at this time.
Since the displacement of 02 is adjusted to stop, the drive of sybarp 102 is stopped as long as the input signal does not change thereafter.

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

As the input signal level increases, the loop drive signal I becomes
ξ≧δ2), the comparator 28 is still “L”
Although the large capacity exhaust valve 18 is kept in a non-communicating state by outputting a level signal, the output of the comparator 26 is at the ``H'' level, and the large capacity air supply valve 16 is kept in a communicating state.

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

Therefore, the drive pressure chamber 101 is connected to the air pressure source (pm) via two valves, the three-way switching valve 14 and the large-capacity air supply valve 16.
When communicating with the drive pressure chamber 101, the pressure supplied to the drive pressure chamber 101 rises rapidly, and the valve 102 is largely displaced. In other words, it responds quickly to a large increase in input.

Due to the displacement of the valve 102, the value of e becomes smaller [-
δ1≦1≦δ1], the process returns to the next pulse width modulation operation as 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 output of the comparator 26 go to "L" level. The output of the comparator 28 becomes "H" level. Accordingly, the three-way switching valve 14 puts the air pipe 12 and the air pipe 22t in communication, puts the large capacity air supply valve 16 in a non-communicating state, and puts the large capacity air supply valve 18 in a communication state.

Therefore, the drive pressure chamber 101 is in communication with the atmosphere (PO) via the two valves, the three-way switching valve 14 and the large-capacity exhaust valve 18, and the pressure supplied to the drive pressure chamber 101 suddenly drops, causing ε The valve 102 is largely displaced in the opposite direction to when the value of becomes large.

Due to the displacement of the valve 102, the value of I becomes large [-
When δ1≦C≦δ1], the pulse width modulation operation is returned to, as in the above case.

However, here, even if the input signal changes in the same way, the communication with the air pressure source or the atmosphere depends on the load level at that time, the pressure inside the drive pressure chamber 101 before the above change occurs. There is a difference in the response characteristics when

For example, when the load level is as high as 60 to 80%, a normal response is shown to a change in the same input signal that increases or decreases by 20%, but when the load level is 0 to 20%, the response is normal.
At low levels, the response tends to overshoot. The reason for this is that, in this embodiment, the large-capacity intake valve 16 or the large-capacity exhaust valve 18 is opened in response to a change in the input signal and closed when the deviation reaches δ2. and response time, it takes a certain amount of time from the time the electrical signal is sent until the valve actually closes completely, and given the high flow rates, especially at low load levels, excessive flow may occur during this time. This is thought to be due to the fact that it is stored away.

This will be explained in detail #4BVC using figures. Figure 4 (B)) shows the response to the input signal increase of the 25th section for the cases where the load level is 0% (indicated by 0 in the figure) and 75% (indicated by (B) in the figure). Showing the change in pressure in the drive pressure chamber 101 corresponding to the stem position of the valve 102;
) in the figure shows the output of the comparator 26 that drives the large capacity air supply valve 16 at that time.

Assuming that δ2 is 5%, if the input signal increases by 25 qb at 1o as shown by the dashed line in the figure, the deviation C becomes 25% at that point and the large capacity air supply valve 26 opens. When the valve tread detector 30 detects t=5%, the large-capacity intake valve 26 closes, and the desired value is then reached by the movement of the three-way switching valve 14 driven by the pulse width modulation signal. Converge.

However, as shown by the broken line in the figure, the pressure increases exponentially toward VcPM (1.4 y/cm in this example), so the differential coefficient of the pressure at time t1, in other words, the flow rate is , depending on the load level, it is large when the load level is small and small when it is large.In addition, since the response of the air system switch is slower than that of the electric system, the large capacity air supply valve 1
6 is actually 1. Yoshi also closes late. For this reason, when the flow rate is large or the load is low, the valve may exceed the desired value. This problem can be solved by setting a larger value for δ2, but this will result in overdumping when the load is high. Although the case where the input signal suddenly increases 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 responsiveness 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 microcombinator 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 configured using a microcomputer. In the figure, the processor unit receives the AD-converted input signal and the output of the valve lift detector 30, and determines the load level X (step 10).
1). Next, the deviation ζ is calculated, and data relating the load level and the value of a2 as shown in FIG. 6 given in advance in the memory (in the illustrated example, δ2 = 1/x) is used.
The corresponding δ2X is determined from (step 102). Then, check the magnitude relationship between the absolute value of e and δ2 (step 103), and if the former is less than the latter, apply a predetermined pulse width modulation signal to operate the three-way switching valve 14 (step 1
04) If the former is greater than or equal to the latter, the large-capacity air supply valve 16 or the large-capacity exhaust valve 18 is operated depending on the sign of g (step 105). The above processing/program is repeatedly executed at a predetermined period.

In the above-mentioned nine embodiments, the relationship between the load level and the value of 22 is given in advance as fixed data, but if it is acquired by learning at the initial stage of operation, a desirable control suitable for each individual device can be obtained. I can do it.

Figure M7 is a block diagram showing another embodiment of the present invention.

In this embodiment, a means for sealing the pressure in the driving pressure chamber when the deviation is close to zero is added to the next valve positioner shown in Fig. 1g1.

That is, a conventional valve positioner uses a nozzle/75 collar and a pilot relay, but the nozzle/75 collar and pilot relay consume air even in a balanced state. Specifically, in a valve positioner using a semi-bleed type pilot relay or a bleed type pilot relay, the nozzle part and the pilot relay part have 5 to 15
There is an air consumption of Nt/mim.

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

In view of these circumstances, this embodiment has the following features: as described above, even if the deviation between the input signal and the amount of displacement 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 equivalent parts as in FIG. 1 are given the same reference numerals and detailed explanation thereof will be omitted.

As shown in the characteristic diagram of FIG.
However, the "L" level is output only when -60 < 0.0 < δ0 * δ1), and in other cases "L" level is output.
Outputs H'' level.

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

The on/off switching valve 42 includes 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 the air pipe 122 communicating with the drive pressure chamber 101, and 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 the comparator 40 When the output of 40 is at the "r level", the communication state is established.

The gate circuit 44 includes the pulse width modulator 24 and the three-way switching valve 1.
When the output of the comparator 40 is at the "L" level, the output signal is at the "L" level, and when the output of the comparator 40 is at the "H" level, the output signal is pulse width modulated. The output signal of the device 24 is output as is.

Therefore, as shown in FIG. 9, the output of the gate circuit 44 is "L" when (g(-az, -ao<, <δO)
``Level and Nashi.

■When [1>δ1], it is “H” level, ■[-
δ1≦ε≦−δ0. When δO≦6≦δ1], pulse width modulation operation is performed.

Next, the operation of this embodiment will be explained.

The value of valve drive signal I is.

When C - δQ, JQ(g) is satisfied, the same operation as in the embodiment described above is performed, so the explanation thereof will be omitted.

Therefore, the value of the valve drive signal C is -δ0kuIkuδO The operation when this happens is explained below.

When the value of the valve drive signal e falls within the range of [-δ0 x δ0], the three-way switching valve 14 stops the pulse width modulation operation and closes the air pipe 20f. 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 C is C=<δ2]. Therefore, the air supply path from the air pressure source (pm) is completely cut off, and air consumption in this state becomes zero.

On the other hand, the on/off switching valve 42 enters a non-communicating state when the value of the valve driving signal - falls within the range of 1 δO - 8 < δ0, so the air f121 flows through the three-way switching valve 14t to the atmosphere (po ), but the drive pressure chamber 101
The air inside is not exhausted and the position of the valve 102 is held constant.

Note that if the value of the valve drive signal e changes due to a new signal input and becomes outside the range of [-δ0 x C x δO], 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, which indicates the deviation between the input signal and the valve opening degree, is pulse-width modulated and then converted into a pneumatic pressure signal. When the pneumatic control valve is driven, if the deviation indicated by the valve drive signal is larger than a predetermined value, the drive pressure chamber of the pneumatic control valve is communicated with the air pressure source or the atmosphere. Even when the deviation is large, the control valve can be made to respond quickly without using a booster relay. 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 example of the valve positioner of the present invention, FIG. 2 is a characteristic diagram of the pulse width modulator and comparator of the above embodiment, and FIG. 3 is an output waveform diagram of the pulse width modulator. , FIG. 4 is a diagram for explaining the difference in response characteristics depending on the load level, and FIG. 5 is a processing program in the processor unit when configured using the comparator 26, 28 and pulse width modulator 24t-microcomputer. 70-chart showing an example, FIG. 6 is a diagram showing an example of the relationship between the load level and the value of δ2, FIG. 7 is a block diagram showing another embodiment of the valve positioner of the present invention, and FIG. A characteristic diagram of the comparator, and FIG. 9 is a characteristic diagram of the gate circuit. 10...Pneumatic control valve, 101-...Driving pressure chamber, 102...Valve, 12, 121, 122゜20.22...Air pipe, 14...Three-way switching valve ,
16...Large capacity air supply valve, 18...Large capacity exhaust valve, 24...Pulse@modulator, 26°28...Comparator, 30...Valve 7 Detector.

Claims (1)

[Claims] means for pulse-width modulating a valve drive signal indicating the deviation between the input signal and the opening degree of the pneumatic control valve; converting the output signal of the pulse-width modulating means into a pulse-width-modulated pneumatic signal; means for inputting a signal into a driving pressure chamber for displacing the valve opening of the pneumatic control valve; and means for inputting a signal into a driving pressure chamber for displacing the valve opening of the pneumatic control valve; A valve positioner comprising means for communicating with the atmosphere and means for setting the predetermined value to be small when the degree of opening of the valve is large and to be large when the degree of opening of the valve is small.