JP5548158B2 - Positioner - Google Patents

Description

  The present invention relates to a positioner that controls the opening of a control valve.

  Conventionally, a positioner is provided for the control valve, and the position of the control valve is controlled by this positioner. This positioner obtains the deviation between the valve opening setting value sent from the host device and the actual opening value fed back from the control valve, and outputs the electrical signal obtained by applying a predetermined calculation to this deviation. A control unit that outputs the control signal, an electropneumatic converter (EPM) that converts the control output from the control unit into a pneumatic signal, and amplifies the pneumatic signal converted by the electropneumatic converter and outputs the amplified pneumatic signal to the control valve drive A pilot relay (see, for example, Patent Document 1).

  FIG. 3 shows a configuration of a main part of a conventional positioner. In the figure, 1A is a positioner, 2 is a control valve, and the control valve 2 is provided with an opening sensor 3 for detecting the valve opening (opening of the valve). The positioner 1A includes a control unit 11, an electropneumatic converter 12, and a pilot relay 13. The valve opening of the control valve 2 detected by the opening sensor 3 is set to the control unit 11 as an actual opening value Xpv. Feedback is coming.

  In the positioner 1A, the control unit 11 obtains a deviation e between the valve opening set value Xsp from the host device (not shown) and the actual opening value Xpv from the opening sensor 3, and performs a PID control calculation on the deviation e. The electric signal obtained by performing the above is output as the control output MV. The deviation e is calculated by the deviation calculating unit 11a, and the PID control calculation for the deviation e is performed by the PID control calculating unit 11b.

  The electropneumatic converter 12 converts the control output MV from the control unit 11 into an air pressure signal (nozzle back pressure) Pn. The pilot relay 13 amplifies the air pressure signal Pn from the electropneumatic converter 12 and outputs it as air pressure Po to the drive unit 2a of the control valve 2. Thereby, the air of the air pressure Po flows into the diaphragm chamber in the drive part 2a, and the opening degree of the valve 2b of the control valve 2 is adjusted.

  The pilot relay 13 includes a cylinder 13a and a poppet valve 13b as main components. The pilot relay 13 has only one air pressure output port, and the control valve 2 is normally operated (driven in a direction corresponding to the control output MV) by the air pressure Po output from the one output port. Reverse operation (driving in the direction opposite to the control output MV) is performed. This type of positioner is called a single-acting positioner.

  In the case of the control method employed in the positioner 1A, the control unit 11 includes not only the control valve 2 but also an electropneumatic converter 12 and a pilot relay 13 that apply an air flow rate and air pressure to the control valve 2. It is. As long as the characteristics of the electropneumatic converter 12 and the pilot relay 13 are linear and the characteristics are straightforward, such a control method is sufficient. However, in actuality, both the electropneumatic converter 12 and the pilot relay 13 have nonlinear elements such as hysteresis and dead band, and control is complicated. For this reason, this control method has limitations in speed response and settling (stability). Therefore, a control method that improves the speed response of the valve opening control is shown in Patent Document 2, and a control method that improves the settling property of the valve opening control is shown in Patent Document 3.

  FIG. 4 is a diagram showing an outline of the control method disclosed in Patent Document 2. In FIG. In the positioner 1B, the actual opening value Xpv fed back from the control valve 2 to be controlled is set as the first feedback value, while the displacement Xp of the cylinder 13a and the poppet valve 13b in the pilot relay 13 is detected by the position sensor 14. A value Km · Xp obtained by multiplying the displacement Xp detected by the position sensor 14 by a constant Km is used as the second feedback value. Then, the control output MV from the control unit 11 is used as the control output of the major control loop, and the second feedback value Km · Xp is subtracted from the control output MV of the major control loop as the feedback value of the minor control loop to obtain the corrected control output. MV ′ is obtained, and this correction control output MV ′ is used as a control output to the electropneumatic converter 12. The multiplication of the constant Xm to the displacement Xp is performed by a multiplication unit (second feedback value calculation unit) 15, and the subtraction of the minor control loop feedback value Km · Xp from the control output MV of the major control loop is performed by a subtraction unit (correction). Control output calculation unit) 16.

  FIG. 5 is a diagram showing an outline of the control method disclosed in Patent Document 3. As shown in FIG. In this positioner 1C, the actual opening value Xpv fed back from the control valve 2 to be controlled is set as the first feedback value, and the air pressure Po from the pilot relay 13 to the control valve 2 is detected by the pressure sensor 17. The differential value dPo / dt of the air pressure Po detected by the pressure sensor 17 is used as a pressure differential value, and a value Km · dPo / dt obtained by multiplying the pressure differential value dPo / dt by a constant Km is used as a second feedback. Value. The control output MV from the control unit 11 is used as the control output of the major control loop, and the second feedback value Km · dPo / dt is subtracted from the control output MV of the major control loop as the feedback value of the minor control loop for correction. A control output MV ′ is obtained, and this corrected control output MV ′ is used as a control output to the electropneumatic converter 12. The calculation of the pressure differential value dPo / dt and the multiplication of the pressure differential value dPo / dt by a constant Km are performed by the multiplication unit (second feedback value calculation unit) 18 and minor control from the control output MV of the major control loop. The subtraction of the loop feedback value Km · dPo / dt is performed by a subtraction unit (correction control output calculation unit) 19.

Japanese Utility Model Publication No. 62-28118 JP-T-2004-523016 JP 2001-221201 A

  However, in the control method shown in Patent Document 2 (FIG. 4), it is possible to improve the quick response of the valve opening control by shortening the waste time and the time constant, but it is difficult to improve the settling. Further, in the control method shown in Patent Document 3 (FIG. 5), since the pressure value itself is observed, improvement of settling such as overshoot and settling time can be expected, but improvement of rapid response is difficult.

  The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a positioner capable of satisfying both of quick response of valve opening control and improvement of settling. is there.

  In order to achieve such an object, according to the present invention, an actual opening value fed back from a control valve that is a control target is set as a first feedback value, and the first feedback value and a higher-level device are sent. A control means for obtaining a deviation from the valve opening set value and performing a predetermined calculation on the deviation and outputting an electric signal as a control output, and converting the control output from the control means into a pneumatic pressure to drive the control valve In a positioner provided with an electropneumatic conversion means for outputting to an air pressure section, an air pressure detection means for detecting the air pressure from the electropneumatic conversion means to the drive part of the control valve, and a differential value of the air pressure detected by the air pressure detection means Second feedback value calculation means for calculating a second feedback value as a differential value, and a differential value of an actual opening value fed back from the control valve as a valve opening differential value A third feedback value calculating means for calculating the feedback value, an adding means for calculating the sum of the calculated second feedback value and the third feedback value as a feedback value of the minor control loop, The control output is taken as the control output of the major control loop, and the correction control output is obtained by subtracting the feedback value of the minor control loop calculated by the adding means from the control output of this major control loop, and this correction control output is electro-pneumatic converting means. And a correction control output calculation means for outputting as a control output.

  According to the present invention, the air pressure from the electropneumatic conversion means to the drive portion of the control valve is detected, and the second feedback value is calculated using the detected differential value of the air pressure as the pressure differential value. For example, a value obtained by multiplying the pressure differential value by a first constant is calculated as the second feedback value. Further, the third feedback value is calculated using the differential value of the actual opening value fed back from the control valve as the valve opening differential value. For example, a value obtained by multiplying the valve opening differential value by the second constant is calculated as the third feedback value. The sum of the second feedback value and the third feedback value is used as the feedback value of the minor control loop, and the correction control output is obtained by subtracting the feedback value of the minor control loop from the control output of the major control loop. The obtained correction control output is used as a control output to the electropneumatic conversion means.

  In the present invention, the sum of the second feedback value and the third feedback value is, for example, the air output from the electropneumatic conversion means by giving an appropriate value as the first constant or the second constant described above. It is possible to make it an amount corresponding to the flow rate. In this case, the amount corresponding to the flow rate of the air output from the electropneumatic conversion means is subtracted from the control output of the major control loop, and both the quick response and the stability of the valve opening control are compatible. Become.

  According to the present invention, the second feedback value is calculated using the differential value of the air pressure to the drive portion of the control valve as the pressure differential value, and the differential value of the actual opening value fed back from the control valve is calculated as the valve opening differential value. Since the third feedback value is calculated as the value, and the sum of the calculated second feedback value and the second feedback value is used as the feedback value of the minor control loop, it is output from the electropneumatic conversion means. By subtracting the amount corresponding to the flow rate of the air from the control output of the major control loop, it is possible to improve both the quick response and the settling of the valve opening control.

It is a figure which shows the structure of the principal part of one Embodiment (Embodiment 1 (single action type)) of the positioner which concerns on this invention. It is a figure which shows the structure of the principal part of other embodiment (Embodiment 2 (double acting type)) of the positioner which concerns on this invention. It is a figure which shows the structure of the principal part of the conventional positioner. It is a figure which shows the outline of the control system shown by patent document 2. FIG. It is a figure which shows the outline of the control system shown by patent document 3. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1: Single-acting positioner]
FIG. 1 is a diagram showing a configuration of a main part of an embodiment (embodiment 1) of a positioner according to the present invention. 5, the same reference numerals as those in FIG. 5 denote the same or equivalent components as those described with reference to FIG. 5, and the description thereof will be omitted.

  In this positioner 1D, a differential value Xpv / dt of the actual opening value Xpv fed back from the control valve 2 is used as a valve opening differential value, and a value Kn ·· obtained by multiplying the valve opening differential value dXpv / dt by a constant Kn. Using dXpv / dt as the third feedback value, a sum FB of the second feedback value Km · dPo / dt and the third feedback value Kn · dXpv / dt is obtained (FB = Km · dPo / dt + Kn · dXpv / dt). ), The sum FB of the second feedback value and the third feedback value is used as the feedback value of the minor control loop. The control output MV from the control unit 11 is used as the control output of the major control loop, and the correction value MV ′ is obtained by subtracting the feedback value FB of the minor control loop from the control output MV of this major control loop. The output MV ′ is a control output to the electropneumatic converter 12.

  The calculation of the valve opening differential value dXpv / dt and the multiplication of the valve opening differential value dXpv / dt by a constant Kn are performed by the multiplication unit (third feedback value calculation unit) 20, and the second feedback value Km · The addition unit 21 calculates the sum FB of dPo / dt and the third feedback value Kn · dXpv / dt. The subtraction unit (correction control output calculation unit) 22 subtracts the feedback value FB of the minor control loop from the control output MV of the major control loop.

  In this positioner 1D, the pressure sensor 17 detects the air pressure Po from the pilot relay 13 to the drive unit 2a of the regulating valve 2. The multiplication unit (second feedback value calculation unit) 18 calculates the differential value dPo / dt of the air pressure Po detected by the pressure sensor 17 as a pressure differential value, and adds a constant Km (first value) to the pressure differential value dPo / dt. The value Km · dPo / dt multiplied by the constant) is output as the second feedback value.

  The multiplication unit (third feedback value calculation unit) 20 branches and inputs the actual opening value Xpv from the opening sensor 3, and the differential value dXpv / dt of the actual opening value Xpv is the valve opening differential value. And a value Kn · dXpv / dt obtained by multiplying the valve opening differential value dXpv / dt by a constant Kn (second constant) is output as a third feedback value.

  The adding unit 21 adds the second feedback value Km · dPo / dt from the multiplying unit 18 and the third feedback value Kn · dXpv / dt from the multiplying unit 20, and feeds the added value back to the minor control loop. The value FB is sent to the subtraction unit (correction control output calculation unit) 22.

  The subtraction unit (correction control output calculation unit) 22 inputs the control output MV from the control unit 11 as the control output of the major control loop, and subtracts the feedback value FB of the minor control loop from the control output MV of this major control loop. Thus, a correction control output MV ′ is obtained, and this correction control output MV ′ is used as a control output to the electropneumatic converter 12.

  In this positioner 1D, the sum of the second feedback value Km · dPo / dt and the third feedback value Kn · dXpv / dt is obtained by setting the first constant Km and the second constant Kn to appropriate values. The amount corresponds to the flow rate of air output from the pilot relay 13. Thus, the valve opening degree control is performed by subtracting the amount corresponding to the flow rate of air output from the pilot relay 13 from the control output MV of the major control loop, that is, using the feedback value FB of the minor control loop as the flow rate equivalent physical quantity. It improves both quick response and settling.

[Derivation of flow equivalent physical quantity]
Hereinafter, the theory that “Km · dPo / dt + Kn · dXpv / dt” obtained as the feedback value FB of the minor control loop is an amount corresponding to the flow rate of air output from the pilot relay 13 (flow rate equivalent physical quantity). Explain the basic support.

  A relational expression between the flow rate that flows (or flows out) into the diaphragm chamber of the drive unit 2a of the control valve 2, the valve opening degree, and the output air pressure is obtained. Here, P is the pressure of the diaphragm chamber, V is the volume of the diaphragm chamber, θ is the temperature of the diaphragm chamber, A is the effective area of the diaphragm chamber, X is the valve opening, W is the amount of gas in the diaphragm chamber, Let R be the gas constant.

First, the diaphragm chamber is considered using a gas equation of state. Now, for the air in the diaphragm chamber, the equation of state is expressed by the following equation (1).
P ・ V = W ・ R ・ θ ・ ・ ・ ・ (1)

Assuming that the valve operation is isothermal, the above equation (1) is fully differentiated,
P · dv / dt + V · dP / dt = R · θ · dW / dt (2)
Since the mass flow rate G is represented by the time change of W, when formula (2) is arranged for dW / dt,
G = dW / dt = [1 / (R · θ)] · (P · dv / dt + V · dP / dt) (3)

Here, the volume change of the diaphragm chamber is expressed as the following equation (4) by the valve opening X.
dv / dt = A · dX / dt (4)
Substituting the equation (4) into the equation (3), the following equation is obtained as the relationship between the mass flow rate G, the pressure differential value, and the valve opening differential value.
G = dW / dt = [1 / (R · θ)] · (V · dP / dt + P · A · dX / dt] = Km · dP / dt + Kn · dX / dt (5)

  As described above, if the pressure differential value dP / dt and the valve opening differential value dX / dt are sensed and appropriate constants Km and Kn are given, “Km · dP / dt + Kn · dX / dt” drives the control valve 2. It can be seen that it is obtained as an amount (flow equivalent physical quantity) corresponding to the flow rate to the diaphragm chamber of the part 2a.

[Embodiment 2: Double-acting positioner]
FIG. 2 is a diagram showing a configuration of a main part of another embodiment (embodiment 2) of the positioner according to the present invention. 1, the same reference numerals as those in FIG. 1 denote the same or equivalent components as those described with reference to FIG. 1, and the description thereof will be omitted.

  In this positioner 1E, the pilot relay 13 has two air pressure output ports, outputs the air pressure Po1 from the first port, and outputs the air pressure Po2 from the second port. In this positioner 1E, when the control valve 2 is operated normally (driven in a direction corresponding to the control output MV), the air pressure Po1 of the first port is made higher than the air pressure Po2 of the second port, and the control valve 2 is When performing reverse operation (driving in the direction opposite to the control output MV), the air pressure Po2 of the second port is set higher than the air pressure Po1 of the first port. This type of positioner is called a double-acting positioner.

  In this positioner 1E, a differential pressure sensor 23 is provided instead of the pressure sensor 17 shown in FIG. 1, and the difference between the air pressure Po1 of the first port and the air pressure Po2 of the second port to the drive unit 2a of the control valve 2 is provided. The pressure ΔPo (ΔPo = Po1−Po2) is detected, and the detected differential pressure ΔPo is sent to the multiplication unit (second feedback value calculation unit) 18.

  Then, the multiplication unit (second feedback value calculation unit) 18 calculates the differential value dΔPo / dt of the differential pressure ΔPo from the differential pressure sensor 23 as a pressure differential value, and a constant Km ( A value Km · dΔPo / dt multiplied by the first constant) is output to the adding unit 21 as a second feedback value.

  The adder 21 adds the second feedback value Km · dΔPo / dt from the multiplier 18 and the third feedback value Kn · dXpv / dt from the multiplier 20, and feeds the added value back to the minor control loop. The value FB is sent to the subtraction unit (correction control output calculation unit) 22.

  The subtraction unit (correction control output calculation unit) 22 inputs the control output MV from the control unit 11 as the control output of the major control loop, and subtracts the feedback value FB of the minor control loop from the control output MV of this major control loop. Thus, a correction control output MV ′ is obtained, and this correction control output MV ′ is used as a control output to the electropneumatic converter 12.

  In this positioner 1E, the sum of the second feedback value Km · dΔPo / dt and the third feedback value Kn · dXpv / dt is obtained by setting the first constant Km and the second constant Kn to appropriate values. The amount corresponds to the flow rate of air output from the pilot relay 13. Thus, the valve opening degree control is performed by subtracting the amount corresponding to the flow rate of air output from the pilot relay 13 from the control output MV of the major control loop, that is, using the feedback value FB of the minor control loop as the flow rate equivalent physical quantity. It improves both quick response and settling.

  In the second embodiment, the differential pressure sensor 23 detects the differential pressure ΔPo between the first port air pressure Po1 and the second port air pressure Po2 to the drive unit 2a of the control valve 2. Alternatively, the air pressure Po1 of the first port and the air pressure Po2 of the second port may be individually detected, and the differential pressure ΔPo may be obtained as a difference between the detected air pressures Po1 and Po2.

  In the first and second embodiments described above, the control unit 11 performs the PID control calculation on the deviation e between the valve opening set value Xsp and the actual opening value Xpv from the opening sensor 3. The calculation performed on the deviation e is not limited to the PID control calculation. Further, the actual opening Xpv is branched and given to the PID control calculation unit 11b, and a differential preceding type PID control calculation is performed on the deviation e so that the actual opening Xpv is differentiated first. Also good.

In the first and second embodiments, the combination of the electropneumatic converter 12 and the pilot relay 13 corresponds to the electropneumatic conversion means referred to in the present invention.
In the first and second embodiments described above, the opening degree sensor 3 is provided outside the positioner 1D, but may be provided inside the positioner 1D.

  The positioner of the present invention can be used in various fields such as process control as a device that converts an electrical signal into a pneumatic signal and controls the valve opening of the control valve based on the converted pneumatic signal.

  1D, 1E ... Positioner, 2 ... Control valve, 2a ... Drive unit, 2b ... Valve, 3 ... Opening sensor, 11 ... Control unit, 11a ..., 11b ... PID control calculation unit, 12 ... Electropneumatic converter, 13 ... Pilot relay, 13a ... cylinder, 13b, 13b1, 13b2 ... poppet valve, 17 ... pressure sensor, 18 ... multiplier (second feedback value calculator), 20 ... multiplier (third feedback value calculator), 21 ... addition part, 22 ... subtraction part (correction control output calculation part), 23 ... differential pressure sensor.

Claims (3)

The actual opening value fed back from the control valve to be controlled is set as the first feedback value, and a deviation between the first feedback value and the valve opening setting value sent from the host device is obtained. A control means for outputting an electrical signal obtained by performing a predetermined operation on the control output;
In a positioner comprising electropneumatic conversion means for converting the control output from the control means into air pressure and outputting it to the drive portion of the control valve,
Air pressure detection means for detecting air pressure from the electropneumatic conversion means to the drive portion of the control valve;
Second feedback value calculating means for calculating a second feedback value using a differential value of the air pressure detected by the air pressure detecting means as a pressure differential value;
Third feedback value calculating means for calculating a third feedback value using a differential value of the actual opening value fed back from the control valve as a valve opening differential value;
Adding means for calculating a sum of the calculated second feedback value and third feedback value as a feedback value of a minor control loop;
The control output from the control means is used as the control output of the major control loop, and the feedback value of the minor control loop calculated by the adding means is subtracted from the control output of the major control loop to obtain the correction control output. And a correction control output calculation means for outputting an output as a control output to the electropneumatic conversion means. The positioner as claimed in claim 1,
The second feedback value calculation means includes:
A value obtained by multiplying the pressure differential value by a first constant is used as the second feedback value.
The third feedback value calculation means includes
A positioner obtained by multiplying the valve opening differential value by a second constant is used as the third feedback value. The positioner as claimed in claim 1,
The electropneumatic conversion means includes
When the control valve is driven in the direction corresponding to the control output, it has a first port and a second port as an output port of air pressure to the drive portion of the control valve. When the air pressure is higher than the second port air pressure, and the control valve is driven in the opposite direction to the control output, the air pressure of the second port is higher than the air pressure of the first port. ,
The air pressure detecting means includes
Detecting a differential pressure between the air pressure of the first port and the air pressure of the second port of the electropneumatic conversion means;
The second feedback value calculation means includes:
A differential value of the differential pressure detected by the air pressure detection means is set as a pressure differential value, and a value obtained by multiplying the pressure differential value by a first constant is calculated as the second feedback value.
The third feedback value calculation means includes
The differential value of the actual opening value fed back from the control valve is a valve opening differential value, and a value obtained by multiplying the valve opening differential value by a second constant is calculated as the third feedback value. And positioner.

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