JPS6262001A - Valve positioner - Google Patents

Abstract

PURPOSE:To enable a valve positioner to operate at high speed response when it is necessary by usually regulating air pressure in the drive pressure chamber of a pneumatic regulation valve in accordance with air pressure signal which is modulated in its pulse width while communicating the drive pressure chamber with an air pressure source or the similar when input signal is varied greatly. CONSTITUTION:In a pneumatic regulation valve 10, its valve body 102 has its opening regulated by air pressure which is supplied in a drive pressure chamber 101. One end of an air pipe 12 is connected to the drive pressure chamber 101 while the other end is connected to a three-way switching valve 14 and on/off switching valves 16 and 18 for air supply and discharge respectively. The value of voltage from an input module 32 is compared with that from a valve position detector 30 by a comparing part 36, and the obtained potential difference is sent to both a pulse width modulator 24 and an on/off switching valve controlling part 40. In normal operation, air pressure in the drive pressure chamber 101 is regulated in accordance with air pressure signal subjected to pulse width modulation, and if input signal is varied greatly, the drive pressure chamber 101 is communicated with the air pressure source or the atmosphere by said controlling part 40.

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 target valve opening given by an input signal and the actual valve opening to the nozzle/flapper as a mechanical displacement amount, and the nozzle back pressure of this nozzle/flapper is expressed as a pneumatic signal. After taking out the air, the pilot relay amplifies the pressure and supplies it to the air motor of the control valve.

[Problem that the invention aims 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 valve opening 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]

The valve positioner of the present invention has been made in view of the above problems, and includes means for pulse width modulating a deviation signal indicating the deviation between the input signal and the valve opening of the pneumatic control valve, and the pulse width modulating means. means for converting the output signal into a pulse width modulated pneumatic pressure signal and applying the pneumatic pressure signal to a driving pressure chamber for varying the valve opening of the pneumatic control valve; means for communicating the drive pressure chamber with an air pressure source or the atmosphere when the value becomes larger than a predetermined value; and a predetermined relationship based on the deviation and the initial movement speed of the pneumatic control valve when the input signal changes. The apparatus further includes means for disconnecting the driving pressure chamber from the air pressure source or the atmosphere when the time calculated based on the above information has elapsed.

[Effect]

At all times, the air pressure in the drive pressure chamber is adjusted based on the pulse width modulated air pressure signal, and if the input signal changes significantly, the drive pressure chamber is communicated with the air pressure source or the atmosphere by other means. Furthermore, this communication time is calculated based on a predetermined relationship from the initial movement speed of the pneumatic control valve at the time of communication.

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

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, an on-off switching valve 16 for large-capacity air supply, and an on-off switching valve 1 for large-capacity exhaust.
8 is connected.

The three-way switching valve 14 is connected to an air pressure source (Ps) in addition to the air pipe 12.
and an air pipe 22 communicating with the atmosphere (Vent). 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 on-off switching valve 16 for large-capacity air supply and the on-off switching valve 18 for large-capacity exhaust are operated to connect and disconnect the air pipe 20 and the air pipe 12, and to connect the air pipe 22 and the air pipe 12, respectively, by signals from a switching valve driving means 45, which will be described later. This is a switching valve that connects and disconnects the

The valve opening detector 30 detects the opening of the valve 102 and outputs a voltage value VTD corresponding to the opening as a valve opening signal, and is connected to a rotary encoder or a valve 7.
It can be configured with a 98g meter or the like.

The input module 32 converts an input signal of 4 to 20++ A, which is input from the input terminal 34 and represents the target valve opening, into a voltage value Vs.
a is compared with the voltage value VTD from the valve opening degree detector 30 in the comparator 36 .

The potential difference between the voltage value Vs and the voltage value VTD represents the deviation ε between the valve opening indicated by the input signal and the actual valve opening. 40 is input.

As shown in the characteristic diagram of FIG. 2, the pulse width modulator 24 has the following characteristics:
The deviation ε indicated by the manually generated deviation signal Vε is -δ1≦ε≦δ
1. Pulse width modulation is performed on the deviation signal Vε only when the condition (1) is satisfied. The duty ratio when ε=-61 is ``0'', the duty ratio when ε-δl is ``IJ'', and the relationship between ε and the duty ratio when formula (1) is satisfied is linear. There are 9.

The waveform diagram in FIG. 3 shows the output waveform of the pulse width modulator 24 when ε=εl, that is, when the duty ratio is '0.7J, and 70% of the repetition period T is "H".
The remaining 30% is at "L" level.

When the deviation ε satisfies -δ1 (2), the output of the pulse width modulator 24 is "L" in the binary signal.
” level, and the deviation ε is ε〉δ1
...Pulse width modulator 24 when satisfying (3)
The output becomes an "H" level in a 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. 20 and air pipe 22 and air pipe 1.
Connect 2.

The on/off switching valve control unit 40 receives the deviation signal ■ε, the signal (voltage value Vs) output from the input module 32, and the valve opening signal (voltage value VTD) output from the valve opening detector 30.
) to control the on/off switching valves 16 and 18, including a deviation determining means 41, an input signal change detecting means 42, a valve driving speed detecting means 43, a switching valve operating time setting means 44, and a switching valve driving means 45. Consisting of

The deviation determining means 41 takes in the deviation signal ■ε at the signal input timing from the input signal change detecting means 42, and if the deviation ε satisfies ε>δ2 (where δ2 )δ1)... A drive signal for the exhaust on/off switching valve 16 is output, and when ε<-62 (4) is satisfied, a drive signal for the exhaust on/off switching valve 18 is output. Note that the input signal change detection means 42 detects the input signal, that is, the voltage value Vs output from the input module 32.
This means monitors changes in the input signal and outputs a predetermined signal when a change in the input signal is detected.

Valve drive speed calculation means 43 is input signal change detection means 4
This is means for calculating the moving speed of the valve 102 after inputting the signal from 2. That is, immediately after inputting the signal from the input signal change detection means 42, the valve opening signal VTDI from the valve opening detector 30 is input, and furthermore, the valve opening signal VTD2 after a predetermined time Tc is input.

Then, the driving speed V of the valve 102 is calculated by taking the difference between the two valve opening signals and dividing by a predetermined time Tc. Equation (5) expresses this calculation.

v= (VTD2-VTDI)/Tc...(5
) The switching valve operating time setting means 44 is the on/off switching valve 16.
Alternatively, the operation time Ts of 18 is calculated according to the following formula % formula % (6). Here, τd indicates the response time of the on-off switching valves 16 and 18, that is, the time required from when an electric signal is applied until the valves actually close, and is a constant determined by the switching valves.

Note that the deviation signal V in the switching valve operation time setting means 44
The acquisition of ε is performed at the time when the signal from the input signal change detection means 42 is input.

The switching valve driving means 45 operates (communicates with the air pressure source or the atmosphere) either the on/off switching valve 16 or 18 based on the signal from the deviation determining means 41, and based on the signal from the switching valve operating time setting means 44. to stop the operation.

Next, the operation of this embodiment configured as described above will be explained.

When the deviation ε is −δ2 and ε<δ2, the deviation determination means 41 selects the on/off switching valve 1.
6.18 is not selected, and the on/off switching valve 16.
18 is maintained in a stopped state. Therefore, air is supplied and discharged to and from the drive pressure chamber 101 exclusively by the three-way switching valve 14.

For example, the value of the deviation ε given from the comparator 36 is
When δ1 (0<δ1 × δ1) as shown in the figure, only the pulse width modulation operation is performed regardless of changes in the input signal of the input module 32, and neither the on/off switching valves 16 and 18 operate. That is, both the large-capacity air supply on/off switching valve 16 and the large-capacity exhaust on/off switching valve 18 are in a disconnected state, and the driving pressure chamber 101
The air pressure source (Ps) and the atmosphere (Vent) are communicated only through the three-way switching valve 14.

Since the three-way switching valve 14 is currently driven by a pulse width modulation signal with a duty ratio of 0.7, the driving pressure chamber 101
The air pipe 12 communicating with the air pipe 20, that is, the air pressure source (Ps) for 70% of the repetition period T,
0% of the time is communicated with the air pipe 22, ie, the atmosphere (Vent). Therefore, air at the air pressure [(Ps) is gradually supplied to the drive pressure chamber 101, and along with this, the valve 1
The opening degree of 02 gradually changes.

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

The pneumatic control valve 10 adjusts the valve 1 at the supplied air pressure at this time.
Since the displacement of valve 102 is adjusted to stop, the driving of valve 102 will stop unless the input signal changes thereafter.

Here, if the input signal changes greatly and becomes ε=ε2 (>δ2), the input signal change detection means 42 detects the deviation determination means 41, the valve drive speed calculation means 43, and the switching valve operating time setting means 44. outputs a predetermined signal.

The deviation determining means 41 determines from the value of the deviation signal Vε and outputs a signal to drive the air supply on/off switching valve 16, and the switching valve driving means 45 drives the air supply on/off switching valve 16 based on this signal. (communicates with air pressure source).

On the other hand, the valve driving speed calculation means 43 calculates the valve driving speed V based on equation (5). The switching valve operation time setting means 44 also determines the deviation ε and the valve driving speed V from (6
), and outputs an operation stop signal to the switching valve driving means 45 when the operating time Ts has elapsed based on the start of operation of the air supply on/off switching valve 16.

The switching valve driving means 45 stops the operation of the air supply on/off switching valve 16 based on the operation stop signal from the switching valve operation time setting means 44.

Conversely, when the deviation ε significantly changes to 162 or less, the exhaust on/off switching valve 18 is similarly driven.

Note that the three-way switching valve 14 operates regardless of the operation of the on/off switching valves 16 and 18. Therefore, even when the air supply on/off switching valve 16 is in operation as described above, the three-way switching valve 14 is in communication with the air pressure source (Ps) as seen in FIG. This means that air is supplied from both on/off switching valves 16.

In this way, the movement speed V of the valve 102 immediately after the start of operation of the on-off switching valve 16 or 18 is determined, and the operating time Ts is then calculated based on this V, since the valve 102 for the same supply air pressure or exhaust air pressure is
This is because the moving speed of the valve 102 is not necessarily constant due to the opening degree of the valve 102 at that time or the packing friction that changes over time. In other words, the valve 102
If the operating time Ts of the on/off switching valve 16°18 is calculated with the moving speed of
rshoot) L/ta reover dump (Overd
u+sp). Therefore,
After calculating the initial moving speed V of the valve 102, the operating time Ts is calculated based on equation (6), and the deviation ε
When the value becomes approximately zero, the on/off switching valve 16 or 18
It is possible to stop the operation of the Moreover, (
6) Equation is the response time τd of the on/off switching valves 16 and 18.
The accuracy is extremely high as it also takes into account the following.

Note that in calculating the operating time Ts, a straight line estimation was performed for simplicity, but since the moving speed V originally changes based on an exponential curve ', estimation may be performed using the exponential curve.

FIG. 4 is a flowchart when the on/off switching valve control section 40 is constructed from a well-known microcomputer.

First, the output voltage value Vs of the input module 32, the output voltage value VTDI of the valve opening degree detector 30, and the deviation signal Vε output from the comparator 36 are taken in (process 101). Then, the mode status is checked (decision 102). The mode state is related to the operation of the on/off switching valve 16 or 18 as described later, and in the judgment 102 the mode is "1".
" indicates that either the on/off switching valve 16 or 18 is operating, and "0" indicates that neither of them is operating.

Here, if the mode is "0", the process proceeds to judgment 106 and it is determined whether the deviation ε is "-δ2 - ε<δ2". If it is affirmative, the process returns to process 101.

If it is negative, one of the on/off switching valves 16 and 18 should be operated, and the deviation ε will continue to be “ε<δ2”.
It is determined whether or not the following is satisfied (determination 107). Does this judgment cause the air supply on/off switching valve 16 to operate? (Process 1
08), whether to operate the exhaust on/off switching valve 18 (
This corresponds to the judgment of process 109).

After executing either process 108 or 109, when a predetermined time Tc has elapsed (determination 110), the signal from the valve opening degree detector 30 is taken in as signal VTD2 (process 111). Next, the valve 10 immediately after opening the on/off switching valve 16 or 18 based on equation (5)
Step 112): find the moving speed V of 2, and then calculate the operating time Ts of the on/off switching valve based on equation (6) from this moving speed V and the deviation ε taken in step 101.
Set the mode error flag and return to process 101 (process 1
13).

After executing process 101 again, mode 1 is confirmed in decision 102 and the process proceeds to decision 103. In judgment 1゜3, the voltage value V
It is determined whether or not s (input signal) has changed, and if the voltage value Vs has not changed, processing 112 is performed starting from the start of the on/off switching valve operation in processing 108 or 109.
Determine whether or not the operating time Ts calculated in (
Judgment 114). Processing 1.1 and judgments 102, 103, and 114 are repeated until the operating time Ts has elapsed, and when the operating time Ts has elapsed, the mode 1 flag is reset.
Close the on/off switching valve (decisions 115 and 136). The deviation ε at this time should be approximately zero.

Further, if it is detected in judgment 103 that the voltage value Vs has changed, the mode 1 flag is reset and the on/off switching valve is closed (processing 104.105), and then judgment 1
Processes 06 to 113 are executed again. That is, when the voltage value Vs, which is the input signal, changes, the operating time Ts is newly calculated. Of course, in this case, if the absolute value of the deviation ε is smaller than 62 due to a change in the voltage value Vs, the process returns directly from the judgment 106 to the process 101, and the on/off switching valve does not operate.

〔Effect of the invention〕

As explained above, according to the valve positioner of the present invention, the air pressure in the driving pressure chamber is always adjusted based on the pulse width modulated air pressure signal, and when the input signal changes significantly, the driving pressure is adjusted by another means. The chamber is in communication with a source of air pressure or the atmosphere. Moreover, this communication time is calculated based on a predetermined relationship from the initial movement speed of the pneumatic control valve at the time of communication, so even if the deviation between the input signal and the valve displacement is large, it will not work as with conventional devices. The control valve can be made to respond quickly without using a booster relay.

[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 of the embodiment, FIG. 3 is an output waveform diagram of the pulse width modulator, and FIG. 4 1 is a flowchart of the on/off switching valve control section 40 in the embodiment of FIG. IO...Pneumatic control valve, IO■...Drive pressure chamber, I
Q 2-H/L/B, 12,121,122,20.
22...Air pipe, 14...Three-way switching valve, 16...
On/off switching valve for large capacity air supply, 18... On/off switching valve for large capacity exhaust, 24... Pulse width modulator, 3o...
・Valve opening detector, 32...input module, 36
... Comparison section, 40 ... On-off switching valve control section, 41
. . . Deviation determination means, 42 . . . Input signal change detection means, 43. . . . Valve driving speed calculation means, 44 . . . Switching valve operation time setting means, 45 . . . Switching valve operation time setting means.

Claims (1)

[Claims] means for pulse width modulating a deviation signal indicating the deviation between the input signal and the valve opening of the pneumatic control valve; and converting the output signal of the pulse width modulation means into a pulse width modulated air pressure signal to convert the air pressure signal into a pulse width modulated air pressure signal. means for applying pneumatic pressure to the driving pressure chamber for displacing the valve opening of the pneumatic control valve; and means for communicating with the drive pressure chamber and the air pressure source or the atmosphere when a time period calculated based on a predetermined relationship from the deviation and the initial movement speed of the pneumatic control valve when the input signal changes has elapsed. A valve positioner characterized by comprising means for releasing communication with the atmosphere.