Created on:2021-12-21 13:40

Fault diagnosis system of hydraulic equipment based on parameter measurement

Fault diagnosis system of hydraulic equipment based on parameter measurement

Whether a hydraulic system works normally depends on two main working parameters, namely, whether the pressure and flow are in normal working state, and whether the parameters such as system temperature and actuator speed are normal. The fault phenomena of hydraulic system are various, and the fault causes are also the synthesis of many factors. The same factor may cause different fault phenomena, and the same fault may correspond to many different causes. For example, oil pollution may cause faults in the pressure, flow or direction of the hydraulic system, which brings great difficulties to the fault diagnosis of the hydraulic system.

The idea of fault diagnosis by parameter measurement method is as follows: when any hydraulic system works normally, the system parameters work near the design and set value. If these parameters deviate from the predetermined value, the system will fail or may fail, that is, the essence of the failure of the hydraulic system is the abnormal change of the system working parameters. Therefore, when the hydraulic system fails, there must be a failure of one or some components in the system. It can be further concluded that the parameters of one or more points in the circuit have deviated from the predetermined value. This indicates that if the working parameters of a certain point in the hydraulic circuit are abnormal, the system has failed or may have failed, and the maintenance personnel need to deal with it immediately. In this way, on the basis of parameter measurement, combined with logical analysis method, the fault can be found quickly and accurately. Parameter measurement method can not only diagnose system faults, but also predict possible faults, and this prediction and diagnosis are quantitative, which greatly improves the speed and accuracy of diagnosis. This kind of detection is direct measurement, with fast detection speed, small error and simple detection equipment. It is easy to be popularized and used in the production site. It is suitable for the detection of any hydraulic system. During the measurement, it does not need to stop the machine and does not damage the hydraulic system. It can detect almost any part of the system. It can not only diagnose the existing faults, but also monitor and predict the potential faults on line.

1. Principle of parameter measurement method

As long as the working parameters at any point required in the hydraulic system circuit are measured and compared with the normal value of the system, we can judge whether the system working parameters are normal, whether there is a fault and the location of the fault.

The working parameters in the hydraulic system, such as pressure, flow and temperature, are non electro physical quantities. When using general instruments to measure them by indirect measurement method, these non electric quantities need to be converted into electric quantities by using physical effects, and then processed by amplification, conversion and display. The measured parameters can be represented and displayed by the converted electrical signals. Thus, it can be judged whether there is a fault in the hydraulic system. However, this indirect measurement method requires various sensors, the detection device is complex, the measurement result error is large and not intuitive, which is not convenient for field popularization and use.

Now a simple and practical fault detection circuit of hydraulic system is introduced. The system structure principle is shown in figure a (a). The detection circuit is usually connected in parallel with the tested system. This connection needs to set the double ball valve tee joint shown in figure a (a) at the tested point, which is mainly used for non disassembly detection of the system. It can directly and quickly detect various parameters of the required points of the hydraulic system without any sensors. It can detect three parameters of pressure, flow and temperature in the system at the same time, and the speed and speed of the actuator can be calculated by measuring the outlet flow. For example; As long as the double ball valve tee is installed at the pump outlet and the inlet and outlet of the actuator, as shown in Figure B, the approximate position of the fault (pump source, control transmission part or actuator part) can be diagnosed immediately by measuring the pressure, flow and temperature values at points 1, 2 and 3. By adding parameter detection points, the fault area can be reduced.

Detection principle: as shown in figure a (a). When the system works normally, valve 1 is opened and valve 2 is closed, and the dust cover is installed on the detection mask to prevent pollution. During detection, as long as the detection circuit is connected with the detection port, tighten the union thread and open valve 2. The parameters such as pressure, flow, temperature and speed can be easily measured by adjusting valve 1 and overflow valve 7. However, when the system piping is required, the double ball valve tee shall be used as a connecting pipe [see Fig. a (a) connection] or elbow joint [see Fig. a (10) connection] at the position where the system parameters need to be detected, which will not increase the complexity of the system or have a significant impact on the system performance.

2. Parameter measurement method

(1) Measure the pressure. As shown in figure a (a), first screw the hose connector of the detection circuit to the tee threaded interface of the double ball valve; Open the ball valve 2, close the overflow valve 7 and cut off the oil return channel. At this time, the pressure value of the measured point (the actual working pressure of the system) can be directly read out from the pressure gauge 4.

(2) Measure flow and temperature. Slowly loosen the handle of overflow valve 7 and then close ball valve 1. Readjust the overflow valve 7 so that the reading of pressure gauge 4 is the measured pressure value, and the reading of flowmeter 5 is the actual flow value of the measured point. At the same time, the oil temperature value can be displayed on thermometer 6.

(3) Measure the speed (speed). Regardless of the pump, hydraulic motor or cylinder, its speed or speed only depends on two factors, namely, the flow and its own geometric size (displacement or area). Therefore, as long as the output flow of the hydraulic motor or cylinder (input flow for the pump) is measured and divided by its displacement or area, the speed or speed value can be obtained.

3. Conclusion

Parameter measurement method is a practical and new fault diagnosis method of hydraulic system. Combined with logic analysis method, it greatly improves the rapidity and accuracy of fault diagnosis. Firstly, this measurement is quantitative, which avoids the blindness and experience of personal diagnosis, and the diagnosis results are in line with the reality. Secondly, the fault diagnosis speed is fast. The accurate parameters of the system can be measured after a few seconds to tens of seconds, and then the diagnosis results can be obtained after simple analysis and judgment by the maintenance personnel. Moreover, compared with the traditional fault diagnosis method, this method reduces the workload of system assembly and disassembly by more than half.

This fault diagnosis detection loop has the following functions.

(1) It can directly measure and visually display the liquid flow, pressure and temperature, and indirectly measure the speed of pump and hydraulic motor.

(2) The overflow valve can be used to simulate and load the measured part of the system, and the pressure regulation is convenient and accurate; In order to ensure the accuracy of the measured flow, the test temperature difference can be directly observed from the thermometer (it shall not exceed ± 3 ℃).

(3) It is applicable to any hydraulic system, and some system parameters can be detected without stopping.

(4) The utility model has the advantages of light and simple structure, reliable operation, low cost and simple operation. The detection circuit combines the loading device with a simple detection instrument, and can be made into a portable detector. The measurement is fast, convenient and accurate, and is suitable for popularization and use in the field. It lays a foundation for the automation of detection, prediction and fault diagnosis.

Home    Article    Fault diagnosis system of hydraulic equipment based on parameter measurement