JPH0724641Y2 - Electro-pneumatic positioner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an electro-pneumatic positioner that receives a current signal and obtains valve opening information from this current signal and also serves as a circuit power source, and particularly provides a high-speed response. The present invention relates to an electropneumatic positioner improved so as to obtain stability.

<Prior Art> FIG. 7 is a block diagram showing the configuration of a conventional electropneumatic positioner of this type. This electro-pneumatic positioner is, for example,
It is disclosed in No. 61-125088 (name of device: electro-pneumatic positioner), the outline of which is described below.

I ₀ is a current signal, such as 2 from the output end of the controller, etc.
It is input to the current / voltage conversion circuit 10 as a current signal of 4 to 20 mA through the book transmission line.

The current / voltage conversion circuit 10 is composed of, for example, a series circuit of a zener diode and an input resistor, and the voltage generated at both ends of this zener diode serves as the power source of the circuit, and the input voltage Vi becomes the input voltage at both ends of this input resistor. Convert.

The converted input voltage Vi is deviated from the feedback signal Vf ₁ from the displacement / voltage signal conversion circuit 11 by ε ₁ to obtain a constant multiple of the amplifier 1.
Output to 2.

The output of the amplifier 12 is input to the actuator 13. The actuator 13 is, for example, the output voltage from the amplifier 12 to the piezoelectric element fixed to the upper and lower end of the flapper is applied is converted into a predetermined driving voltage, it is stretchable in response to the deviation epsilon ₁ and displaced d _1. This displacement d ₁ is detected by the nozzle flapper mechanism 14 and converted into pressure P ₁ and output to the control relay 16 via the changeover switch 15 for switching between automatic / manual operation.

The control relay 16 amplifies the pressure P ₁ to drive pressure P ₂ and supplies it to the valve 17 to displace its stem. The displacement X ₁ of the stem is applied to the displacement / voltage signal conversion circuit 11 and becomes the feedback signal Vf ₁ .

The actuator 13, the nozzle flapper mechanism 14, the changeover switch 15, and the control relay 16 constitute a voltage / pneumatic pressure conversion unit 18.

As described above, the current signal I ₀ is transferred to the corresponding valve.
Convert to 17 stem displacement.

<Problems to be Solved by the Invention> However, in the electropneumatic positioner that returns the stem of the valve to the input side as described above, the responsiveness and stability of the stem tend to conflict with each other. In other words, if the amplification factor of the amplifier is increased to realize a high-speed response, oscillation becomes easier and the stability is lowered. Conversely, if the amplification factor is reduced, the overshoot is reduced, but the response becomes slower.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a deviation signal which is a deviation between a current input for controlling the opening of the valve and a feedback signal corresponding to the position of the valve valve shaft. In an electro-pneumatic positioner that amplifies the above with an amplifier and drives the previous valve via the voltage / pneumatic pressure conversion unit, when the previous deviation signal is larger than a predetermined deviation, the amplification degree of the previous amplifier is increased to increase the deviation signal. A variable means for automatically reducing the amplification degree when it becomes small is provided in the main loop so that it converges quickly and stably to the valve opening corresponding to the target current signal. .

<Operation> When the deviation signal is larger than the predetermined deviation, the amplification degree of the amplifier is increased, and when the deviation signal becomes small, the amplification degree is automatically decreased to quickly and stably reach the target valve opening degree. To converge.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a main part of one embodiment of the present invention.

Reference numeral 20 is a deviation amplifier, which is composed of an operational amplifier Q ₁ and resistors R _{1 to} R ₄ .

The operational amplifier Q ₁ has a resistor between the output terminal and the inverting input terminal (-).
R ₁ is connected to the non-inverting input terminal (+) of which the input voltage Vi from the current / voltage conversion circuit 10 is input via the resistor R ₂ and is also connected to the common potential point COM via the resistor R _3. The feedback signal Vf ₂ is fed back to the inverting input terminal (−) via the resistor R ₄ .

With the above configuration, the input voltage Vi is applied to the output terminal of the deviation amplifier 20.
And a deviation signal ε ₂ corresponding to the deviation between the feedback signal Vf ₂ and the feedback signal Vf ₂ .

The deviation signal ε ₂ is input to the variable amplifier 21 and also to the window comparator 22.

The window comparator 22 includes comparators Q ₂ , Q ₃ , resistors R _{5 to} R ₇ ,
And variable resistance VR.

Inverting input of the comparator Q ₂ (-) and the comparator non-inverting input terminal of Q ₃ (+) deviation signal epsilon ₂ is input to the resistor R ₅ and a variable resistor
The limit value e ₁ obtained by dividing the power supply voltage (+ Vcc / 2) and (-Vcc / 2) by VR and the resistor R ₆ is the non-inverting input terminal (+) of the comparator Q _2.
And the limit value −e ₁ is applied to the inverting input terminal (−) of the comparator Q ₃ , respectively. The output terminals of the comparators Q ₂ and Q ₃ are connected in common and are pulled up to the power supply voltage + Vcc / 2 by the resistor R ₇ .

The variable amplifier 21 includes an operational amplifier Q ₄ , resistors R _{8 to} R ₁₀ ,
Consists of switch SW ₁ .

The deviation signal ε ₂ is applied to the non-inverting input terminal (+) of the operational amplifier Q ₄ in which the resistor R ₈ is connected between the output terminal and the inverting input terminal (−), and its inverting input terminal (−) is Through the switch SW ₁ , one end is switched to the resistor R ₉ and the resistor R ₁₀ connected to the common potential point COM.

The switch SW ₁ is switched by the window voltage Vw at the output ends of the comparators Q ₂ and Q ₃ to change the amplification degree of the variable amplifier 21.

The output voltage V ₀ of the variable amplifier 21 is input to a circuit similar to the voltage / pneumatic pressure conversion unit 18 shown in FIG. 7, converted into drive pressure P ₃ , and applied to the valve 17. Displacement X _{2 of} valve 17 is 7th
It is input to a circuit similar to the displacement / voltage signal conversion circuit 11 shown in the figure and fed back to the deviation amplifier 20 as a feedback signal Vf ₂ .

Next, the operation of the circuit shown in FIG. 1 configured as described above will be described with reference to FIGS. 2 and 3. FIG. 2 is a characteristic diagram showing the characteristic of the window comparator, and FIG. 3 is a characteristic diagram showing the characteristic of the variable amplifier.

The deviation signal ε ₂ of the deviation amplifier 20 is the window comparator 22.
Entered in. As shown in FIG. 2, when the deviation signal ε ₂ is e ₁ <| ε ₂ |, the window comparator 22 shows that the window voltage Vw becomes −Vcc / 2 and the switch SW ₁ is connected to the resistor R ₉ to obtain the result shown in FIG. As shown, the amplification degree of the variable amplifier 21 is set to G _1, and conversely, when the deviation signal ε ₂ is e ₁ ≧ | ε ₂ |, the window voltage Vw becomes + Vcc / 2 and the switch SW ₁ is connected to the resistor R _10. As shown in FIG. 3, the amplification degree of the variable amplifier 21 is increased to G ₂ (G ₁ <G ₂ ). The value of this limit value e ₁ is determined by increasing or decreasing the variable resistance VR.

As described above, when the deviation signal ε ₂ is small with the predetermined limit value e ₁ as a boundary, the amplification degree of the variable amplifier 21 is small,
If it is large, the amplification is set to be large, and in the initial state where the deviation is large, the valve opening is quickly approached to the target valve opening, and when the predetermined limit value e ₁ is reached, the amplification is reduced and overshoot is prevented. It is possible to prevent and ensure stability.

The above situation is shown in FIG. 4 when the horizontal axis represents time t and the vertical axis represents displacement X ₂ of the valve stem.

When the input signal Vi changes stepwise, the deviation is large at the beginning, so the displacement X ₂ corresponding to the input signal Vi is rapidly approached with a large amplification degree G ₂ , but when the deviation reaches a predetermined limit value e ₁ , amplification is performed. It is switched to G ₁ with a small degree and quickly stabilizes as shown by the solid line. On the other hand, it can be seen that the response in the conventional case in which the amplification factor is kept large at G ₂ is overshooting to a considerable extent as shown by the dotted line.

FIG. 5 is a block diagram showing a main part configuration of another embodiment of the present invention. This embodiment shows a case where it is realized by digital calculation.

For the input signal, for example, the analog input signal Vi is converted to analog /
The signal is converted into a digital signal by the digital converter and converted into a digital input signal Vi (D), which is input to one input terminal (+) of the subtractor 23. At the other input terminal (-), the displacement X ₂ of the valve stem is converted into a digital signal by using, for example, an oscillation amplifier and the digital feedback signal Vf
It is entered as ₂ (D). The subtractor 23 performs a subtraction between these input signal Vi (D) and the feedback signal Vf ₂ (D) to obtain a digital deviation signal ε ₂ (D), which is 1 at the input ends of the multiplier 25 and the comparator 24. Output to one. A digital reference signal V _S (D) is applied to the other end of the input end of the comparator 24,
The comparator 24 compares these and outputs the multiplication factor selection signal V _M (D) to the multiplier 25.

The multiplier 25 performs multiplication on the deviation signal ε ₂ (D) according to the multiplication factor determined by the multiplication factor selection signal V _M (D), performs digital / analog conversion, and outputs a voltage as an analog output voltage V _0. / Outputs to the air pressure conversion unit 18 (FIG. 1).

FIG. 6 is a block diagram showing the configuration of the third essential embodiment of the present invention.

The deviation signal ε ₂ is output to the non-inverting input terminal (+) of the operational amplifier Q ₄ of the variable amplifier 21 and the comparators 26, 27, 28.
Are output respectively. Between the inverting input terminal (-) of the operational amplifier Q ₄ and the common potential point COM, the switch SW ₂₃ inserted in series with the resistor R ₉ , the switch SW ₂₂ inserted in series with the resistor R ₁₀ , and the resistor R Switch S inserted in series with ₁₁
W ₂₁ are connected in parallel.

The comparator 26 turns on the switch SW ₂₁ when | ε ₂ | ≦ e ₁ , the comparator 27 turns on the switch SW ₂₂ when e ₁ <| ε ₂ | ≦ e ₂ , and the comparator 28 outputs the deviation signal ε ₂ Operates to turn on the switch SW _{23 in} a range other than these. However, these limit values have a relationship of e ₁ <e ₂ .
With the above configuration, the amplification degree can be automatically converted into three levels according to the magnitude of the deviation signal.

In the above description, the electro-pneumatic positioner has been described. However, the content is, for example, a feedback signal obtained by converting the pneumatic output of the voltage / pneumatic pressure conversion unit 18 into a voltage signal using a pressure / voltage converter instead of the displacement of the stem. It can also be applied to an electropneumatic converter that feeds back to a deviation amplifier.

<Effect of the Invention> As described above in detail with the embodiments, the present invention is
The electro-pneumatic positioner's amplification factor is configured to be variable according to the amount of deviation, so that the stem (shaft) of the valve (valve) responds at high speed and suppresses the overtravel of the stem to improve stability. be able to.

[Brief description of drawings]

1 is a block diagram showing an essential part of one embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining the operation of the window comparator shown in FIG. 1, and FIG. 3 is an operation of the variable amplifier shown in FIG. FIG. 4 is a characteristic diagram showing characteristics of the circuit shown in FIG. 1, FIG. 5 is a block diagram showing essential parts of a second embodiment of the present invention, and FIG. FIG. 7 is a block diagram showing a main part of the third embodiment, and FIG. 7 is a block diagram showing a configuration of a conventional electropneumatic positioner. 10 …… current / voltage conversion circuit, 11 …… displacement / voltage signal conversion circuit, 12 …… amplifier, 13 …… actuator, 14 …… nozzle flapper mechanism, 17 …… valve, 18 …… voltage / pneumatic conversion circuit, 20 …… Deviation amplifier, 21 …… Variable amplifier, 22…
… Window comparator, 23 …… Subtractor, 24 …… Comparator, 25 …… Multiplier, 26, 27, 28 …… Comparator, Vi…
… Input signal, Vf ₁ , Vf ₂ …… Feedback signal, ε ₁ , ε ₂ …… Deviation signal, V ₀ …… Output voltage.

Claims (1)

[Scope of utility model registration request] 1. A valve which amplifies a deviation signal, which is a deviation between a current input for controlling the opening of the valve and a feedback signal corresponding to the position of the valve shaft of the valve, by an amplifier and through a voltage / pneumatic pressure converter. In the electro-pneumatic positioner for driving the variable position control means for increasing the amplification degree of the amplifier when the deviation signal is larger than a predetermined deviation and automatically decreasing the amplification degree when the deviation signal becomes small in the main loop. An electro-pneumatic positioner, which is provided to quickly and stably converge to a target valve opening corresponding to the current signal.