JPH05187405A - Valve positioner - Google Patents

Abstract

PURPOSE:To reduce the cost of a valve positioner by providing a time difference detecting means receiving a valve opening degree detection signal and a diagnosis initiating signal so that occurrence of abnormality is determined when a detected time difference exceeds a normal time difference. CONSTITUTION:An input circuit 30 delivers a voltage signal Vi corresponding to a current signal Ii received from an adjuster or the like, and a controlling and computing circuit 32 compares the voltage signal Vi with a feed-back signal from a valve opening degree detecting circuit and delivers a drive signal VD corresponding to the deviation between therebetween, to an pneumatic pressure generating mechanism 34 so as to cause an adjusting valve 6 to deliver an operating pressure Po. In this phase, when a diagnosis signal generating circuit 35 delivers a diagnosis signal, a time measuring circuit 36 measures the time period between the time when the diagnosis signal is received and the time when the valve opening degree detecting circuit 33 receives a valve opening degree variation signal DELTAVA, and if thus measured time period is shorter than a predetermined time period, an abnormality determining circuit 37 determines occurrence of an abnormality so as to energize an alarm generating circuit 38.

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 the flow rate of various fluids, and more particularly to predicting a fluid leak in a gland packing of the control valve. The present invention relates to a valve positioner improved.

[0002]

2. Description of the Related Art FIG. 4 is a configuration diagram showing a configuration of a conventional control valve. The control valve 6 is composed of a main body 2 that controls the flow rate of the process fluid 1, and a diaphragm-type operating portion 4 that reciprocates the valve plug 3 in the main body 2 in the axial direction. Furthermore, a valve positioner 5 for adjusting the valve opening degree according to the current signal I _{i of 4} to 20 mA transmitted thereto is added.

In the main body 2, the process fluid in the upstream passage 10 is seated at the seat ring 12 at the center of the partition wall 11.
It is configured so as to pass through the fitted opening to the downstream passage 13. Then, 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 connected to the stem 18 of the operating portion 4 and the stem connector. It is connected via 19. The stem 18 is biased 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 connected through the stem connector 19 also moves upward and the valve of 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 plug 3 moves downward and the valve opening decreases.

The pressure of the pressure chamber 23 is adjusted by the valve positioner 5. The valve positioner 5 receives the current signal I _i indicating the valve opening from the input terminal 7, detects the valve opening by the lever 24 that rotates with the vertical movement of the stem 18, and feeds back the value to determine the actual value. The pressure of the air chamber 23 is adjusted so that the valve opening degree matches the valve opening degree corresponding to the current signal I _i .

In such a control valve, a pressing member 25 for pressing the gland packing 17 in order to improve the sealing performance of the plug insertion hole 16 is provided on the upper lid 15, and the process from the plug insertion hole 16 is performed. The fluid 1 is prevented from leaking.

As the pressing member 25, a packing follower 2 having a central hole through which the upper rod 3a of the valve plug 3 passes.
6, a packing flange 27 placed on the packing follower 26, and a plurality of stud bolts 28 and nuts 29 that press the packing flange 27 against the packing follower 26. The bolts 28 are screwed into the screw holes of the upper lid 15. Has been.

Since the gland packing 17 gradually loosens due to wear or the like, the pressing member 25 is appropriately retightened to optimize the tightening pressure, and the gland packing 17 itself is replaced as necessary.

However, the degree of progress of the looseness of the gland packing 17 varies depending on the material of the gland packing 17 and the installation conditions of the control valve. Moreover, with respect to the detection of the looseness, the maintenance person checks the looseness of the bolt 29 of the pressing member 25, or when the process fluid 1 is a liquid, the leakage state is visually monitored from the upper portion of the plug insertion hole 16. It is monitored manually, such as by doing.

Then, as a proposal for solving this problem, there is a practical valve 63-173501 "valve positioner".
This proposal stores the air pressure at the time when the timing signal from the timing generation means is input by using the pressure detection means, and further stores the air pressure at the time when the valve lift starts to change after inputting this timing signal, A leak abnormality is detected by comparing the difference between these air pressures with a reference air pressure.

[0012]

However, when it is necessary to cover the circuit power source of the positioner with the limited power of only the current signal of 4 to 20 mA transmitted from the two transmission lines, the current consumption is required. Since it is necessary to use a pressure detecting means for operating the leak detecting means, specifically, a pressure sensor, extra power is consumed, there is a restriction when incorporating other functions, and the cost is further increased. There is.

[0013]

In order to solve the above problems, the present invention receives a current signal via two transmission lines to make a circuit power supply with an input circuit and to generate this current signal. In the valve positioner that controls the valve opening of the previous control valve by inputting the valve opening signal related to the valve opening of the control valve through the valve opening detection circuit and calculating these deviations by the control operation circuit. Diagnostic signal generating means for outputting a diagnostic signal to the preceding control arithmetic circuit, a valve opening detection signal from the preceding valve opening detecting circuit and a diagnostic start signal from the preceding diagnostic signal generating means are inputted. The time difference detection means for detecting the time difference between the signals, and the abnormality determination means for comparing the output of the time difference detection means with a predetermined normal time difference signal to determine an abnormality. Turn off the valve opening signal of And a diagnosis start signal and the valve opening degree detecting signal is obtained to detect the time difference in the previous time difference detecting means.

[0014]

[Operation] The diagnostic signal generating means outputs the diagnostic signal to the control arithmetic circuit which feeds back the signal related to the transmitted current signal and the valve opening signal and controls and calculates them. The valve opening detection signal from the valve opening detection circuit and the diagnosis start signal from the preceding diagnostic signal generating means are input to the time difference detecting means, and the time difference detecting means detects the time difference between these signals.

The abnormality determining means compares the output of the time difference detecting means with a predetermined normal time difference signal to determine an abnormality.
When an abnormality is detected, the valve opening signal to the control arithmetic circuit is turned off, and the time difference detecting means detects the time difference from the diagnosis start signal and the valve opening detection signal. Know process fluid leaks without using

[0016]

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. It should be noted that parts having the same functions as those of the conventional control valve shown in FIG.

A current signal I _i of 4 to 20 mA is input to the input terminal 7 from a controller or the like via two transmission lines (not shown). The current signal I _i is the input circuit 30 with which to make a constant voltage E _b of the circuit power source to be used in this positioner 31, simultaneously outputs a voltage signal V _i corresponding to the current signal I _i.

This voltage signal V _i is inputted to one end of the input of the control arithmetic circuit 32, and the valve opening detection circuit 33 is provided to the other end.
The feedback signal V _{f from} is input. The control calculation circuit 32 calculates the deviation between the voltage signal V _i and the feedback signal V _f and outputs the drive signal V _D to the pneumatic pressure generating mechanism 34 at its output end.

The air pressure generator mechanism 34 is supplied with a supply air pressure P _S, the drive signal V _D by using the supply air pressure P _S
The operating pressure P ₀ corresponding to is output to the control valve 6. The air pressure generating mechanism 34 applies, for example, a drive signal V _D to a drive circuit for driving an electromagnetic drive actuator, and applies a displacement corresponding to a drive current flowing therewith to a nozzle / flapper mechanism to convert it into an air pressure signal. This is amplified by a pyret relay or the like and output as the operating pressure P ₀ .

The control valve 6 moves its stem STM up and down in response to this operating pressure P ₀ . This movement is controlled by the control valve 6
The valve opening degree V _A is changed, but this movement is also output to the valve opening degree detection circuit 33. Here, it is converted into a feedback signal V _f as an electric signal corresponding to the valve opening degree V _A , and the feedback signal V _f is output to the control arithmetic circuit 32.

Further, the diagnostic signal generation circuit 35 outputs the diagnostic start signal CH1 and the diagnostic signal CH2 to the control arithmetic circuit 32 and outputs the diagnostic start signal CH3 to the time measuring circuit 36.

Further, valve opening degree detecting circuit 33 outputs a change signal [Delta] V _A of the valve opening degree V _A to time measuring circuit 36. The time measuring circuit 36 measures the time from the reception of the diagnosis start signal CH3 to the reception of the change signal ΔV _A. The measured value is output to the abnormality determination circuit 37.

The abnormality judging circuit 37 judges that the measurement time is abnormal if the measured time is a predetermined time T ₀ or less and outputs it to the alarm generating circuit 38. Next, the operation of the embodiment configured as described above will be described with reference to the characteristic diagram shown in FIG.

When the positioner 31 is operating normally and the leak of the process fluid from the gland packing 17 is to be diagnosed, the diagnostic signal generation circuit 35 first informs the control arithmetic circuit 32 of the diagnostic start signal CH1. Is output.

The feedback start signal CH1 is used to cut the feedback signal V _f from the valve opening degree detection circuit 33, which is a feedback circuit, to minimize the valve opening degree V _A. Next, the diagnostic signal CH2 is output to the control arithmetic circuit 32 to maximize the valve opening degree V _A of the control valve 6, for example.

At this time, at the same time, the diagnostic signal generating circuit 35 also outputs the diagnostic start signal CH3 to the time measuring circuit 36. Let these times be t ₀ . The time measuring circuit 36 starts the control valve 6 from the time t _{0 when the} diagnosis start signal CH3 is received.
There measured time difference between time t ₁ until receiving a change signal [Delta] V _A to start moving (t ₁ -t _0). The characteristic at this time is characteristic A shown in FIG. Similarly, the characteristic B is a measurement of the time difference (t ₃ −t ₂ ).

These time differences correspond to the looseness of the gland packing of the control valve 6. Characteristic B is measured before the start of operation with the control valve 6 installed. Characteristic A shows the characteristic that the gland packing and the rod are loosened during operation and friction is reduced.

Therefore, when the value of the time difference (t ₁ -t ₀ ) or the time difference (t ₃ -t ₂ ) exceeds the set value, it indicates that the gland packing has loosened, and this is measured by the time measurement. It is measured by the circuit 36. The reason why the diagnostic signal generation circuit 35 cuts the feedback signal V _f from the valve opening degree detection circuit 33 prior to the diagnosis will be described with reference to FIG.

Voltage signal V_iAnd feedback signal V_fIs the control calculation time
The deviation is calculated on the path 32, and the drive signal V_DIs pneumatic
Raw mechanism 34 (gain is G₀) Is output to the control valve 6
The displacement of the valve is detected by the valve opening detection circuit 33 (transfer function is H).
Converted to pressure signal and feedback signal V _fHas been negatively fed back as
It

At this time, there is a relationship of (P ₀ / V _i ) = G ₀ / (1 + G ₀ H). However, when G ₀ = 20, G ₀ H> 1 and 90 (normally 30 to 150) are calculated, (P ₀ / V _i ) =
It becomes 0.2.

However, _{if the} feedback signal V _f is cut here, (G ₀ /0.2)=(20/0.2)=100, and the operating pressure P ₀ can be greatly changed with a slight input signal. it can. In the above description, the valve opening degree is changed from the minimum value to the maximum value, but the present invention is not limited to this and may be changed from the maximum value to the minimum value.

[0032]

As described above in detail with reference to the embodiments, according to the present invention, by sending a diagnostic signal to the control calculating means and the time measuring means, the response time difference of the control valve can be marked, and thus the pressure It is not necessary to use a conversion sensor or the like, the wear state of the gland packing of the control valve can be easily measured, and it is extremely effective in a two-wire positioner or the like in which the power source used is limited. By taking such a measure, the looseness of the packing can be detected in advance, countermeasures can be taken at an early stage, and the plant will not be stopped.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram explaining an operation of the embodiment shown in FIG.

FIG. 3 is another explanatory diagram explaining the operation of the embodiment shown in FIG.

FIG. 4 is a configuration diagram showing a configuration of a conventional control valve.

[Explanation of symbols]

 2 Main body section 4 Operation section 5 Valve positioner 6 Control valve 7 Input terminal 17 Gland packing 30 Input circuit 32 Control arithmetic circuit 34 Air pressure generating mechanism 35 Diagnostic signal generating circuit 36 Time measuring circuit 37 Abnormality judging circuit 38 Alarm generating circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takeshi Nishijima 2-932 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. (72) Inventor Hiroshi Hayashi 2-932 Nakamachi, Musashino City, Tokyo Yoko Within Kawa Denki Co., Ltd. (72) Inventor Ryusaku Kubota 2-932 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Co., Ltd. (72) Minoru Midori 2-932 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric machinery Co., Ltd. (72) Inventor Yasuo Kasahara 2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. (72) Akira Inoue 2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd. In the company

Claims (1)

[Claims] 1. A valve opening detection circuit for receiving a current signal via two transmission lines and making a circuit power supply by an input circuit, and at the same time, the current signal and a valve opening signal related to the valve opening of a control valve are detected. In the valve positioner that controls the valve opening of the control valve by calculating these deviations input via
A diagnostic signal generating means for outputting a diagnostic signal to the control arithmetic circuit, a valve opening detection signal from the valve opening detection circuit, and a diagnostic start signal from the diagnostic signal generating means are input, and the time difference between these signals is inputted. The time difference detection means for detecting the time difference, and the abnormality determination means for comparing the output of the time difference detection means with a predetermined normal time difference signal to determine an abnormality. A valve positioner in which the signal is turned off and the time difference detecting means detects a time difference from the diagnosis start signal and the valve opening detection signal.