JPH08219305A - Valve positioner - Google Patents

Abstract

PURPOSE: To diagnose and forecast the abnormality of the operation part of an adjusting valve, by changing the gain of the oscillation limit of a control computing element, in a condition where an input signal is introduced, into upper and lower limit values to detect the existence of the oscillation limit of a system in these values. CONSTITUTION: In a gain change circuit 49, the gain of a control computing element 34 is changed into Gv (L), a lower limit indicating a normal oscillation limit, to set the Gv (L) to the element 34. In an abnormality detection circuit 45, an abnormality-diagnosed signal is outputted by detecting a judgment signal in a lower limit gain value Gs (L) in accordance with the oscillation lilmit. In the circuit 45, when the judgment signal is not detected in the lower limit gain value Gs (L) in accordance with the oscillation limit, the gain of the element 34 is changed into Gv (H), the upper limit of the normal oscillation limit; and an abnormality-diagonosed signal is outputted by detecting the judgment signal Js (H) in an upper limit gain value Gs (H) in accordance with the oscillation limit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve positioner used in a control valve provided in a plant or the like for controlling flow rates of various fluids, and more particularly to a function for controlling the valve opening of the control valve based on an input signal. In addition to the above, the present invention relates to a valve positioner improved so as to also have a diagnostic predictive function of performing diagnostic prediction for an abnormality in the operating portion of a control valve.

[0002]

2. Description of the Related Art FIG. 2 is a structural diagram showing the structure of a conventional valve positioner disclosed in Japanese Utility Model Laid-Open No. 63-173503. Hereinafter, this will be described. This top guide type single seat control valve includes a main body 2 that controls the flow rate of a process fluid (controlled fluid) 1 and a diaphragm type operation portion 4 that causes the main body 2 to reciprocate a valve plug 3 in its axial direction. In addition, a valve positioner 30 for adjusting the valve opening degree according to the input signal I is added.

In the main body portion 2, the process fluid 1 in the upstream passage 10 has the seat ring 1 at the center of the partition wall 11.
2 is configured so as to pass through the fitted opening to the downstream side passage 13.

As the valve plug 3 moves up and down along the guide ring 14, the opening degree of the opening changes and the flow rate of the process fluid 1 is controlled. The upper rod 3a of the valve plug 3 is slidably inserted into the plug insertion hole 16 of the upper lid 15 of the main body via the gland packing 17, and the upper end of the rod 3a is inserted via the stem 18 and the stem connector 19 of the operating portion 4. It is connected.

The stem 18 is urged downward by a spring 20 and its upper end is fixed to the diaphragm 21, and moves up and down according to the pressure in the pressure chamber 23 of the diaphragm case 22.

When the internal pressure of the pressure chamber 23 increases, the stem 18 is pulled upward, and the valve plug 3 connected through the stem connector 19 also moves upward and the valve at the opening provided in the main body 2 is moved. The opening becomes large. Conversely, pressure chamber 2
When the internal pressure of 3 decreases, the valve opening plug 3 moves downward and the valve opening decreases.

The pressure of the pressure chamber 23 is adjusted by the valve positioner 30. The valve positioner 30 inputs a signal indicating the valve opening degree from the input terminal 7, detects the valve opening degree by the lever 24 that rotates with the vertical movement of the stem 18,
The value is fed back to make the actual valve opening equal to the valve opening indicated by the input signal.
3, that is, the pressure of the air chamber is adjusted.

In such a control valve, the operating portion 4 includes a spring case 25 fixed to the stem 18 and the upper lid 15 of the main body, a spring 20 arranged in the spring case 25 and biasing the stem 18 downward. The diaphragm case 22 is arranged on the spring case 25, and the diaphragm 21 is arranged with its peripheral portion held in the diaphragm case 22. The upper end of the stem 18 is connected to the diaphragm 21. There is.

At the connecting portion between the diaphragm case 22 and the spring case 25, a guide bush 26, which is inserted through the stem 18 with an O-ring 27 interposed, is arranged in order to maintain the sealing property of the air chamber 23. A gasket 28 is attached to the outer periphery of the gasket. Reference numeral 29 is a pipe as an air supply path for supplying the air pressure output from the valve positioner 30 to the air chamber 23.

The valve positioner 30 includes an input circuit,
It is composed of a control calculator, an air pressure generator, a valve displacement detector and the like, and the valve opening of the control valve always follows the target valve opening which is a target value given as the input signal I.

Of these, the input circuit controls the built-in input signal I in the form of a current value from the input terminal 7 from the controller (not shown) via two transmission lines (not shown) in the valve positioner 30. The voltage value is converted so that it can be input to the arithmetic unit, and the circuit power supply of the valve positioner 30 is also created.

On the other hand, the valve displacement detector is composed of a potentiometer, a rotary encoder or the like, detects the valve opening degree from the rotation angle of the lever 24 which changes with the valve lift, and converts it into an electric signal. Then, the measured valve opening is output to the control calculator.

Then, the control calculator compares the target valve opening degree from this input device with the measured valve opening degree from the valve lift detector which is interlocked with the lever 24, so that these deviations approach zero. An air pressure control signal is output to the air pressure generator.

Further, the air pressure generator controls the pressure in the air chamber 23 via the pipe 29 by increasing, decreasing or holding the output air pressure based on the air pressure control signal from the control calculator.

[0015]

However, the valve positioner as described above has the following problems.

(A) Impurities and the like contained in the process fluid 1 enter between the valve plug 3 and the guide ring 14 or between the gland packing 17 and the rod 3a, thereby increasing the frictional force and finally "galling". Stem 1
This may be noticed by the operator after the 8 is completely immobile.

(B) Since the gland packing 17 is deteriorated and hardened to lose its elasticity and gradually loosens due to increased friction, a maintenance person regularly checks the packing condition to cause liquid leakage. Manpower was required to visually check whether there was any.

[0018]

As a structure for solving the above problems, the present invention provides a valve opening signal of a control valve detected by a valve displacement detector and a target valve opening indicated by an input signal. In the valve positioner that controls the valve opening of the previous control valve according to the previous air pressure by supplying the air pressure from the control calculator to the operation part of the previous control valve so that they match.
Diagnostic signal generating means for outputting a diagnostic signal for a fixed period of time, gain changing means for outputting a gain changing signal by inputting this diagnostic signal to change the gain of the previous control arithmetic unit, and the previous input signal And the preceding valve opening signal are input, the number of changes calculation means for counting the number of changes in which the difference in the number of occurrences of changes in these signals exceeds a predetermined value within a predetermined time, and the number of changes is a reference value. Judgment signal output means for outputting a judgment signal for judging that the above is reached, and an abnormality for outputting an abnormality diagnosis signal when the previous gain when this judgment signal is output exceeds a preset reference range A detection means is provided, and the oscillation limit is measured by this to perform diagnostic prediction for the previous abnormality of the control valve.

[0019]

[Operation] The diagnostic signal generating means outputs a diagnostic signal for a fixed time during which the diagnostic is performed. The gain changing means outputs the gain changing signal by inputting this diagnostic signal to increase or decrease the gain of the control arithmetic unit to cause the system to oscillate.

An input signal indicating the target valve opening and the valve opening signal of the control valve detected by the valve displacement detector are input to the change number calculating means, and the difference in the number of changes in these signals occurs for a predetermined time. The number of changes that exceeds a predetermined value is counted. Then, the determination signal output means outputs to the abnormality detection means a determination signal for determining that the number of changes has become equal to or greater than the reference value.

The abnormality detecting means outputs an abnormality diagnosing signal when the previous gain when this judgment signal is output exceeds a preset reference range. In this way, the prediction of the abnormality of the control valve is predicted by measuring the oscillation limit.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. The parts having the same functions as those of the conventional valve positioner shown in FIG. 2 are designated by the same reference numerals and the description thereof will be appropriately omitted.

Reference numeral 31 denotes a main control circuit for transmitting an input signal I from a controller (not shown) or the like, and controlling the valve opening of a control valve 32 composed of a main body 2 and an operating portion 4 in response to the input signal I. Is. The main control circuit 31 is mainly composed of an input circuit 33, a control calculator 34, an air pressure generator 35, a valve displacement detector 36 and the like.

The input circuit 33 receives an input signal I as a current signal of 4 to 20 mA from two transmission lines,
The circuit power supply E _b for operating the internal circuit is made at 4 mA or less which is the base portion of the input signal I, and the remaining 0 to 16
The mA is converted into a voltage signal V _i that gives the target value of the valve opening.

The voltage signal V _i is applied to one input end of the control calculator 34, and the control valve 3 is applied to the other input end.
The stroke 2 is detected by the valve displacement detector 36, and this is converted and applied as the valve opening signal V _f .

The control calculator 34 controls the operating portion 4 by the operation signal P ₀ obtained via the air pressure generator 35 so that the voltage signal V _i and the valve opening signal V _f coincide with each other. The operation signal P ₀ moves the stem 18 connecting the main body 2 and the operating part 4 up and down to adjust the valve opening of the main body 2, and the vertical movement of the stem 18 is controlled by the lever 24 that rotates.
6 is output.

Reference numeral 37 is a change count calculation circuit, and this change count calculation circuit 37 is composed of a first differential calculation circuit 38, a second differential calculation circuit 39, a comparison circuit 40, a counting circuit 41 and the like.

The voltage signal V _i corresponding to the portion for controlling the valve opening of the input signal I is input from the input circuit 33 to the differential operation circuit 38, and in order to grasp the degree of change of this voltage signal V _i. This is subjected to a differential operation and output to one end of the input of the comparison circuit 40.

Further, the differential operation circuit 39, via a valve displacement detector 36 is a signal stem 18 moves up and down the valve opening signal V _f satisfies inputted, the change of the valve opening signal V _f In order to grasp the degree, this is subjected to a differential operation and output to the other end of the input of the comparison circuit 40.

The comparison circuit 40 calculates the difference between the rate of change of the voltage signal V _{i and} the rate of change of the valve opening signal V _f , and outputs it to the determination circuit 41 as a difference signal S _D. This difference signal S _D
Since the change of the voltage signal V _i input from the change in the valve opening signal V _f satisfies been erased, the change in purely valve opening signal V _f satisfies been extracted.

The counting circuit 41 has a counting start signal S._CAnd the difference
No. S_DAre input, and the counting start signal S _CStarts counting with
This difference signal S_DChange of the predetermined number N
Counting whether or not the count is exceeded and counting result N_CIs output.

The determination signal output circuit 42 is composed of a reference value setting circuit 43 and a determination circuit 44, and the reference value setting circuit 43 sends to the determination circuit 44 a reference value N _S which is the determination reference of the counting result N _C. and it outputs the determination when it exceeds the decision circuit 44 compares the count result N _C and the reference value N _S, the count result N _C is the reference value N to determine whether or not exceeds the _S criterion N _S The signal J _S is output.

[0033] The abnormality detection circuit 45, the determination signal J _S, and the gain G _S is inputted, will be described later gain range when the judgment signal J _S to obtain the judgment signal _{J S (G S (H)} ~ G _S (L)
When it exceeds, the abnormality diagnosis signal S _A is output.

The diagnostic circuit 46 comprises a timer circuit 47 and a diagnostic signal generator 48. Of these, the timer circuit 47 sets the diagnostic operation time T _C in the diagnostic signal generator 48 at the start of the diagnostic, and outputs the counting start signal S _C to the counting circuit 41.

When the diagnostic operation time T _C is input from the timer circuit 47, the diagnostic signal generator 48 outputs to the gain changing circuit 49 a diagnostic signal T _{S in} which a predetermined level state continues for a certain time.

The gain changing circuit 49 outputs a gain changing signal G _V for changing the gain to a predetermined value to the control calculator 34 while the diagnostic signal T _S continues, and the abnormality detecting circuit 4
The gain value G _S corresponding to the gain change signal G _V is output to 5.

Next, the operation of the valve positioner constructed as above will be described. First, the normal operation will be described. In normal operation, the control calculator 34
Is set to a predetermined gain G _S0 , and
Neither the diagnostic operation time T _C nor the count start signal S _C is output from the timer circuit 47, and the change number calculation circuit 37 and the gain change circuit 49 are in a disconnected state.

In this state, for example, from the adjuster or the like 4 to 2
The input signal I is input to the input circuit 33 as a current signal of 0 mA or the like.
Then, the input circuit 33 uses the current of the base portion of the input signal I, 4 mA, to make the circuit power supply E _b necessary for the circuit operation, and the remaining 0 to 16 mA is used as the target value of the valve opening degree. It is converted into the applied voltage signal V _i .

The control calculator 34 calculates the deviation between the voltage signal V _i and the valve opening signal V _f output from the valve displacement detector 36, and operates the corresponding output signal via the air pressure generator 35. As the signal P ₀ , the displacement of the stem 18 of the operation unit 4 is controlled.

This displacement is negatively fed back to the control calculator 34 as a valve opening signal V _f via the valve displacement detector 36. The control calculator 34 then determines the voltage signal V _i and the valve opening signal V _f.
Since the calculation is performed so that there is no deviation from the above, the valve opening signal V _f coincides with the voltage signal V _i which is the control target value when the system is in equilibrium.

Next, the operation in the case of making a diagnostic prediction for an abnormality in the operating portion of the control valve will be described. In this case, the diagnostic operation time T _C and the counting start signal S _C are supplied from the timer circuit 47 to the signal diagnostic generator 48 and the counting circuit 41, respectively.
Is output to The signal diagnostics generator 48 has a diagnostic operating time T _C.
Is input, the diagnostic signal T _S is output to the gain changing circuit 49.

The gain changing circuit 49 first sets the gain of the control calculator 34 to G _V (L) which is the lower limit indicating the normal oscillation limit.
Then, this is set in the control calculator 34, and the diagnostic operation time T
This is maintained while _C is output. At the same time, the gain value G _S (L) corresponding to this gain G _V (L) is set in the abnormality detection circuit 45.

[0043] In this state, the differential operation circuit 39 is detected by calculating the variation of the valve opening signal V _f by differentiating the valve opening signal V _f. Furthermore, the differential operation circuit 38 outputs the comparison circuit 40 calculates the variation of the voltage signal V _i by differentiating the voltage signal V _i.

The comparison circuit 40 is the differential operation circuit 3 of these.
8 is compared with the calculation result in the differential calculation circuit 39, and the difference signal S _D (L) which is the difference between them is output. This difference signal S _D
(L) since the form of variation has been removed of the voltage signal V _i from the variation of the valve opening signal V _f, and only fluctuation in purely valve opening signal V _f satisfies outputs.

The counting circuit 41 counts whether the change of the difference signal S _D (L) exceeds a preset number N, and when it exceeds the preset number N, the counting result N _C (L ) Is output to the determination circuit 44. The counting circuit 41 determines whether or not the counting result N _C (L) has reached an amount necessary for the determination.

The determination circuit 44 compares the count result N _C (L) and the reference value N _S, a determination signal J _S (L) when the count result N _C (L) exceeds the reference value N _S Output to the abnormality detection circuit 45. It can be seen that the system including the control valve oscillates when the reference value N _S is exceeded.

The abnormality detection circuit 45 outputs the abnormality diagnosis signal S _A (L) when the determination signal J _S (L) is detected at the lower limit gain value G _S (L) corresponding to the oscillation limit. Oscillation occurs at the lower limit gain value G _S (L) in the following cases, for example.

Between the valve plug 3 and the guide ring 14,
When impurities are mixed between the gland packing 17 and the rod 3a, the frictional force increases, so that it becomes lower than the lower limit gain value G _S (L) of the oscillation limit. Further, when the gland packing 17 is deteriorated and hardened, the frictional force increases, so that the gain value G _S (L) at the lower limit of the oscillation limit is increased.
Lower.

If the determination signal J _S (L) is not detected at the lower limit gain value G _S (L) corresponding to the oscillation limit, the abnormality detection circuit 45 will temporarily determine the frictional force in the control valve as compared with the normal case. Has not increased, and the abnormality diagnosis signal S _A (L) is not transmitted as normal, and processing is performed.

Next, if the determination signal J _S (L) is not detected at the lower limit gain value G _S (L) corresponding to the oscillation limit, the gain of the control calculator 34 is set to the upper limit of the normal oscillation limit G _S (L). _The gain is changed to _V (H) by the gain changing circuit 49, which is set in the control calculator 34 and maintained during the output of the diagnostic operation time T _C. At the same time, the abnormality detection circuit 45
Also, a gain value G _S (H) corresponding to this gain G _V (H) is set.

In this state, the differential operation circuit 39 detects the variation of the valve opening signal _Vf by differentiating the valve opening signal _Vf . At this time, the differential operation circuit 38 outputs the comparison circuit 40 calculates the variation of the voltage signal V _i by differentiating the voltage signal V _i.

The comparison circuit 40 is the differential operation circuit 3 of these.
8 and the calculation result of the differential calculation circuit 39 are compared, and a difference signal S _D (H) which is the difference between them is output. This difference signal S _D
(HL) because a form change is the removal of the voltage signal V _i from the variation of the valve opening signal V _f, and only fluctuation in purely valve opening signal V _f satisfies outputs.

The counting circuit 41 counts whether or not the change of the difference signal S _D (H) exceeds a preset number N, and when it exceeds the preset number N, the counting result N _C (H ) Is output to the determination circuit 44. The counting circuit 41 determines whether or not the counting result N _C (H) has reached to the extent necessary for the determination.

[0054] determination circuit 44 compares the count result N _C (H) and the reference value N _S, a determination signal J _S (H) when the count result N _C (H) exceeds the reference value N _S Output to the abnormality detection circuit 45. It can be seen that the system including the control valve oscillates when the reference value N _S is exceeded.

The abnormality detection circuit 45 outputs an abnormality diagnosis signal S _A (H) when the determination signal J _S (H) is detected at the upper limit gain value G _S (H) corresponding to the oscillation limit. Oscillation occurs at the upper limit gain value G _S (H), for example, when the gland packing 17 is loosened. This is because the frictional force is reduced.

Therefore, the abnormality detection circuit 45 determines whether the determination signal J is at the upper limit gain value G _S (H) corresponding to the oscillation limit.
_{If S} (H) is not detected, the frictional force in the control valve is not reduced as compared with the normal case, and the processing is performed assuming that the abnormality diagnosis signal S _A (H) is not sent as normal.

Although the above calculation has been described by using a hardware-based discrete configuration, these functions can also be realized by software using a microcomputer.

[0058]

As described above in detail with the embodiments, according to the present invention, the gain of the oscillation limit of the control calculator is changed to the upper limit value and the lower limit value in the state where the input signal is introduced. By detecting the presence or absence of the oscillation limit of the system in these, it is possible to know the change in the frictional force applied to the stem of the control valve, and to predict or diagnose the abnormality.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing a configuration of a conventional valve positioner.

[Explanation of symbols]

 2 body part 3 valve plug 3a rod 4 operation part 14 guide ring 17 gland packing 18 stem 30 valve positioner 31 main control circuit 32 control valve 33 input circuit 34 control calculator 35 air pressure generator 36 valve displacement detector 37 change count calculation Circuits 38, 39 Differential operation circuit 40 Comparison circuit 41 Judgment circuit 42 Judgment signal output circuit 43 Reference value setting circuit 44 Judgment circuit 45 Abnormality detection circuit 46 Diagnostic circuit 47 Timer circuit 48 Diagnostic signal generator 49 Gain changing circuit

Front Page Continuation (72) Inventor Koji Omura 2-39 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. (72) Masahito Tsuchiya 2-3-9 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. In the company

Claims (1)

[Claims] 1. An air pressure is supplied from a control calculator to an operating portion of the control valve so that a valve opening signal of the control valve detected by a valve displacement detector and a target valve opening indicated by an input signal are matched. As a result, in the valve positioner that controls the valve opening degree of the control valve according to the air pressure, a diagnostic signal generating means that outputs a diagnostic signal for a certain period of time, and a gain change signal is output when this diagnostic signal is input. The gain changing means for changing the gain of the control calculator and the input signal and the valve opening signal are input, and the difference in the number of occurrences of changes in these signals becomes a predetermined value or more within a predetermined time. Change number calculation means for counting the number of changes, a determination signal output means for outputting a determination signal for determining that the number of changes is equal to or greater than a reference value, and the gain when the determination signal is output. A valve positioner characterized by comprising an abnormality detection means for outputting an abnormality diagnosis signal when a preset reference range is exceeded, by which an oscillation limit is measured to make a diagnostic prediction for an abnormality of the control valve. .