CN107515105B

CN107515105B - Electromagnetic valve fault diagnosis method based on plunger vibration signal

Info

Publication number: CN107515105B
Application number: CN201610416109.2A
Authority: CN
Inventors: 王锴; 迈克尔·佩希特; 于海斌; 徐皑冬; 郭海丰; 王志平; 闫炳均; 金妮
Original assignee: Shenyang Institute of Automation of CAS
Current assignee: Shenyang Institute of Automation of CAS
Priority date: 2016-06-15
Filing date: 2016-06-15
Publication date: 2021-03-30
Anticipated expiration: 2036-06-15
Also published as: CN107515105A

Abstract

The invention belongs to the field of equipment fault diagnosis, and particularly relates to a solenoid valve fault diagnosis method based on a plunger vibration signal. The invention forms the electromagnetic valve fault detection system by the constant voltage source, the accelerometer sensor, the waveform generator and other equipment, and realizes the fault detection of the electromagnetic valve. The method includes the steps that an Accelerometer (Accelerometer) sensor is arranged at a certain position of a valve body of an electromagnetic valve, a small-amplitude voltage excitation signal is applied to the electromagnetic valve through a constant voltage source, a signal in a certain frequency range is input to the electromagnetic valve through a waveform generator, the vibration amplitude of the electromagnetic valve under different frequencies is detected, and therefore the natural frequency of the electromagnetic valve is identified. The health state of the electromagnetic valve equipment is evaluated by detecting the change of the amplitude of the vibration signal at the natural frequency of the electromagnetic valve equipment, so that the maintenance activity of the equipment can be effectively guided.

Description

Electromagnetic valve fault diagnosis method based on plunger vibration signal

Technical Field

The invention relates to the field of solenoid valve fault detection, in particular to a solenoid valve fault diagnosis method based on a plunger vibration signal.

Background

An electromagnetic valve is an automated basic element for controlling or adjusting parameters such as direction, flow rate, speed and the like of process fluid, and is widely applied to various industries such as process industry, automobiles, engineering machinery and the like, and the basic structure of the electromagnetic valve is shown in fig. 1.

● solenoid valve failure reason analysis

During operation of the solenoid valve, the equipment is subjected to multiple stresses from the process fluid, the ambient environment, and thermal effects from the solenoid coil. The main failure modes and mechanisms of the solenoid valve are briefly described below.

The solenoid valve plunger serves primarily for switching the process fluid on and off, and is normally in direct contact with the process fluid. To achieve the desired on-off function, the plunger must be constructed of a soft ferromagnetic material, the most commonly used material at present being 430F stainless steel (i.e., low carbon, high chromium stainless steel), which is specifically designed for solenoid valve applications and is suitable for operation in corrosive environments. As the plunger is in direct contact with the process fluid, the plunger can corrode over time. In addition, since the plunger is in direct contact with the plunger tube, friction, abrasion, material loss, and the like may occur during the movement of the plunger. As friction, wear and material wear increase, stick-slip behavior or problems can develop that can cause the valve to seal improperly when closed. At the same time, prolonged exposure of the plunger to the magnetic field generated by the electromagnetic coil may result in permanent magnetization of the plunger, which may lead to incorrect plunger actuation and improper metering of the process fluid. The response of the plunger to the magnetic field can effectively reflect the change of the plunger behavior.

The plunger tube is a barrier between the plunger and the solenoid. The plunger tube functions to protect the solenoid coil from the process fluid while it also introduces magnetic flux into the plunger (rather than around the plunger). The plunger tube is mainly constructed of aluminum or paramagnetic stainless steel (ferromagnetic plunger tubes provide a magnetic field line shunt path, reducing the efficiency of the solenoid valve). The aggressive process fluids and the friction generated during plunger movement will cause wear of the plunger tube, which will generate wear particles that may inhibit plunger movement. When the plunger comes into contact with abrasive particles, the plunger will exhibit an abnormal response in the magnetic field. The abnormal change of the response of the plunger to the magnetic field can be effectively detected by analyzing the accelerometer signal.

The electromagnetic coil generates a magnetic field, and then drives the plunger to move. The wire used for the electromagnetic coil is generally referred to as a magnetic wire and is usually made of copper. In the field of solenoid valves, three types of inter-turn insulation are commonly used: the temperature rating for insulation class E is 120 deg.c, the temperature rating for insulation class F is 155 deg.c, and the temperature rating for insulation class H is 180 deg.c. Coil constructions are generally divided into two categories: a wrap coil and an encapsulated coil. The wrapping coil is composed of a winding shaft and a spool, and then the winding is protected by an insulating tape; the encapsulated coil also has a coil winding around a bobbin or winding, except that the coil is encapsulated or molded with a suitable resin. When current is passed through the coil, thermal effects cause the wire to increase in temperature. If the temperature is too high, the dielectric material between the wires may degrade and fail, and two adjacent wires will form an electrical connection, thereby creating an inter-turn or inter-layer short. Short circuits cause the coil resistance to decrease, which in turn increases the current. At the location of the short circuit, local hot spots of high temperature will develop, resulting in an open circuit. Corrosion can cause necking of the coil and loss of conductive material, which can lead to failure of the coil. The accelerometer is also able to detect changes in the response of the plunger in the magnetic field due to changes in the strength of the magnetic field caused by degradation of the electromagnetic coil.

● existing solenoid valve failure detection technique

Several valve health monitoring techniques have been proposed, some of which are applicable to solenoid valves. The most widely used valve health monitoring technique at present is the partial stroke test. In the method, a position sensor is used to detect a change in position of a valve plunger, thereby enabling valve fault detection [1] - [3 ]. The partial stroke test techniques are explained in detail in documents [4] to [6 ]. However, the partial stroke test has the disadvantage that since many solenoid valves are small, there is not enough internal space to accommodate a position sensor. Further, mathematically, the acceleration is a second derivative of the position signal, and therefore, the fault detection method based on the change in position cannot detect faults that are sensitive only to the acceleration signal.

A series of experiments aiming at the electromagnetic valve health monitoring method are completed by the national laboratory of the United states of Oak Tree Ridge [7] to [9 ]. The proposed method comprises: the inductance of the coil is monitored during the activation of the solenoid valve, the equivalent circuit of the solenoid is modeled, and the current flowing through the solenoid is monitored at increasing voltage. While these methods can provide health information for the solenoid, none provide on-line health monitoring capability.

There are other techniques available to perform solenoid fault diagnosis, such as knowledge of plunger movement and solenoid health by measuring solenoid current [10], but this method gives only indirect measurements of the failure mode of the solenoid, which does not provide actual behavior and degradation of the plunger state; the change in the state of the solenoid plunger is ascertained by measuring the acoustic and electric field signals [11], which has the disadvantage of working only if the solenoid is successfully activated; the method also does not directly reflect the actual degradation state of the solenoid by monitoring the solenoid plunger position [12] by monitoring the phase difference between the voltage and current applied to the solenoid.

Therefore, the invention provides a direct method for monitoring the health condition of the electromagnetic valve aiming at various failure modes of the electromagnetic valve component. The provided technology can not only detect whether the electromagnetic valve can work normally, but also accurately monitor the actual degradation state of the electromagnetic valve, thereby laying a foundation for realizing condition-based maintenance.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a fault diagnosis method for an electromagnetic valve based on a plunger vibration signal.

The technical scheme adopted by the invention for realizing the purpose is as follows: a solenoid valve fault diagnosis method based on a plunger vibration signal comprises the following steps:

fixing an accelerometer for measuring a plunger vibration signal on the electromagnetic valve;

an electronic excitation signal is injected into the electromagnetic valve to generate a magnetic field and make the plunger generate vibration;

piston vibration signals collected by the accelerometer;

analyzing and extracting the piston vibration signal to obtain the amplitude of the natural frequency of the signal;

and comparing the obtained amplitude at the natural frequency with the amplitude at the natural frequency in a healthy state, and further evaluating the health condition of the electromagnetic valve.

The accelerometer is placed on the top of a plunger tube of the electromagnetic valve and can output a vibration signal of the plunger to a magnetic field.

The accelerometer is placed in the plunger tube of the electromagnetic valve, is fixed at the top or the bottom of the plunger and does not influence the movement of the plunger, and outputs a vibration signal of the plunger to a magnetic field.

The amplitude at the natural frequency of the state of health is obtained by:

fixing an accelerometer on a piston tube outside the health electromagnetic valve;

injecting stable electronic excitation signals into the electromagnetic valve through a constant current source to generate a magnetic field, and injecting electric signals with different frequencies into the electromagnetic valve through a waveform generator;

healthy piston vibration signals collected by an accelerometer;

and analyzing and extracting the healthy piston vibration signal, and taking the amplitude at the natural frequency of the signal as the amplitude at the natural frequency of the healthy state.

The invention has the following advantages and beneficial effects:

1. the invention not only can detect whether the electromagnetic valve can work normally, but also can accurately monitor the actual degradation state of the electromagnetic valve, thereby laying a foundation for realizing condition-based maintenance.

2. The sensor is added to the top of the electromagnetic valve to measure the vibration signal, natural frequency and amplitude information is obtained, and various failure modes of the electromagnetic valve assembly can be detected.

3. In the invention, an accelerometer is arranged at a certain position of the valve body, and when the electromagnetic coil is electrified, the device captures the motion state information of the plunger. The information obtained by the accelerometer enables detection of various faults such as contamination and corrosion of the plunger or plunger tube of the solenoid valve, degradation of the solenoid coil, etc.

Drawings

FIG. 1 is a structural diagram of a bidirectional normally open solenoid valve;

wherein, 1, electromagnetic coil; 2. a plunger; 3. a coil housing; 4. a return spring; 5. a plunger tube; 6. a valve body; 7. a seal member; 8. a valve port;

FIG. 2 is a schematic diagram of an accelerometer placed on top of a plunger tube of a solenoid valve;

FIG. 3 is a schematic diagram of an accelerometer being placed on top of a plunger inside a plunger tube of a solenoid valve;

FIG. 4 is a graphical illustration of the vibrational response of a plunger to electromagnetic excitation signals of different RMS voltage levels;

FIG. 5 is a schematic diagram of the hardware components of the experimental system;

FIG. 6 is a schematic data processing diagram of an experiment;

FIG. 7 is a graph showing the results of the experiment.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

The method comprises the steps of placing an Accelerometer (Accelerometer) on the upper part of a valve body, applying a voltage excitation signal with a certain amplitude to the electromagnetic valve, and detecting the failure of the electromagnetic valve by detecting the amplitude and the natural frequency change of a plunger vibration signal. Fig. 1 shows the main components of the solenoid valve.

According to the physical laws of electromagnetism, the force of a magnetic field is proportional to the square of the strength of the magnetic field. The working principle of the electromagnetic valve is as follows: the electromagnetic coil 1 is used to construct a magnetic field, and the plunger 2 moves from a rest position to an operating position under the action of the magnetic field; when the plunger 2 loses its electromagnetic action, it will return to its initial position under the action of the return spring 4. Therefore, measuring the response signal of the plunger 2 to the magnetic field (i.e., the acceleration signal of the vibration of the plunger 2) can directly reflect the health condition of the solenoid valve. For a new valve, the plunger 2 will move from the initial position to the operating position without hindrance by the magnetic field. Due to corrosion of the process fluid and due to environmental and thermal effects of the solenoid 1, the acceleration signal of the plunger vibration will change during solenoid enabling, which can be used to monitor the health of the solenoid.

The accelerometer is placed on the top of the plunger tube of the solenoid valve that senses the movement of the plunger, as shown in FIG. 2. As shown in fig. 3, the accelerometer may also be placed in a position on the plunger inside the plunger tube that directly captures the movement of the plunger. And then, analyzing the vibration signal output by the accelerometer to complete the fault diagnosis of the electromagnetic valve. By analyzing the frequency, time or time-frequency domain characteristics of the vibration signal, the occurrence of a fault can be detected. For example, as the solenoid valve degrades, the amplitude at the natural frequency of the overall solenoid valve system will gradually decrease. Although this method does not require full triggering of the plunger action, the level of the electromagnetic excitation signal must be large enough to cause the plunger to move. Fig. 4 shows the results of a preliminary experiment that has been completed, effectively triggering solenoid plunger action (and identifying the natural frequency) when the RMS voltage is 5V.

The accelerometer must be attached to the outside of the solenoid valve using a fixed substance such as super glue. However, if the solenoid needs to be fully activated during the test, a more adsorptive substance is required, otherwise the accelerometer may be classified with the solenoid during activation. If the accelerometer is placed inside the plunger tube of the solenoid valve, it is necessary to fix the accelerometer on the plunger. Furthermore, since the plunger is usually in direct contact with the process fluid, the corrosion resistance of the accelerometer and its stationary mass must also be considered.

In a laboratory, an experimental system as shown in fig. 5 was set up to validate the proposed method. The system consists of a waveform generator, a power supply, an electromagnetic valve, an accelerometer, a computer and the like. The data collection and processing flow is shown in fig. 6. Using a waveform generator, an electronic excitation signal (V) with different frequencies (20Hz-2MHz) is injected into the solenoid valve _RMS5V). Vibration signals from the accelerometer are collected separately for each particular frequency, thereby identifying the natural frequency value of the solenoid valve system.

Subsequently, the fault was simulated by injecting materials of different nature inside the solenoid plunger tube:

(1) not filled with any material: health (plunger piston can move freely)

(2) Filling soft materials: degraded state (plunger part moving)

(3) Filling a hard material: failure state (plunger full blocking)

Experimental results as shown in fig. 7, it can be found that as the health state of the solenoid valve changes, the amplitude of the vibration signal at the natural frequency of the system decreases, and the effectiveness of the method is verified.

Therefore, in the actual use process, the health state of the electromagnetic valve can be diagnosed by installing the accelerometer on the electromagnetic valve and processing the vibration signal.

Claims

1. A solenoid valve fault diagnosis method based on a plunger vibration signal is characterized by comprising the following steps:

injecting electronic excitation signals with different frequencies into the electromagnetic valve to generate a magnetic field and enable the plunger to vibrate;

the accelerometer collects a plunger vibration signal;

analyzing and extracting the plunger vibration signal to obtain the amplitude of the natural frequency of the signal;

comparing the obtained amplitude at the natural frequency with the amplitude at the natural frequency in a healthy state, and further evaluating the health condition of the electromagnetic valve;

the accelerometer is placed in the plunger tube of the electromagnetic valve, is fixed at the top or the bottom of the plunger, does not influence the movement of the plunger, and outputs a vibration signal of the plunger to a magnetic field;

or the accelerometer is placed on the top of a plunger tube of the electromagnetic valve and can output a vibration signal of the plunger to the magnetic field.

2. The plunger vibration signal-based solenoid valve fault diagnosis method according to claim 1, wherein the amplitude at the natural frequency of the healthy state is obtained by:

fixing an accelerometer on a plunger tube outside the health electromagnetic valve;

the accelerometer acquires a healthy plunger vibration signal;

and analyzing and extracting the healthy plunger vibration signal, and taking the amplitude at the natural frequency of the signal as the amplitude at the natural frequency of the healthy state.