The importance and necessity of development of pressure switch

At present, the transportation of crude oil in China mainly adopts pipeline heating and conveying technology. The crude oil is set up at 40 ~ 90 km intervals in the pipeline to heat and pressurize. In order to reduce energy consumption China's oil pipeline has been modernized to realize computer monitoring. The pressure switch is installed in the outlet and pump outlet manifold to protect the pipeline in the pipeline monitoring system. The pressure switch is also installed to prevent the pump from pumping in the inlet line and the pump inlet line. But the current pressure switch has the following problems:

 

(1) the work is not reliable. It is found repeatedly during the calibration of the station pressure switch. When the given pressure is lower than the set pressure, the pressure switch still does not move, and it is normal again when the object is struck.

 

(2) the user reaction of the wrong action occurred repeatedly when the pressure in the pipeline caused slight fluctuation, which caused the pump to be shaken. Some pressure switches can not be used for a long time, so that the oil pump loses its due protection and brings unsafe factors.

 

(3) the precision is low and the calibration is difficult to be tested in the calibration.

 

(4) the pressure switch cannot be used due to the low pressure of the inlet after the sealing process is relieved.

 

To solve these problems, it is necessary to develop high reliability, high precision and intelligent electronic pressure switch.

 

2. Product structure and key technologies.

 

2.1 structure principle

 

The outer type of intelligent electronic pressure switch is shown in figure 1. Its structure is composed of pressure sensor, motherboard and anti-explosion shell.

 

The principle block diagram of intelligent electronic pressure switch is shown in figure 2.

 

The intelligent electronic pressure switch consists of the following parts:

 

The pressure sensor adopts single crystal silicon intelligent pressure sensor. The sensor has the characteristics of high accuracy (plus or minus 0.075%), high stability (better than 0.1%FS/year), high overpressure and high static pressure (pressure resistance 16 MPa), and range migration ratio (20:1). The single crystal silicon intelligent pressure sensor is used as the sensor part to ensure the control precision and reliability of the intelligent electronic pressure switch.

 

The signal conditioning part is composed of integrated transportation and electronic components, which can adjust the signal of pressure sensors and turn it into a signal acceptable to the microcomputer and send it to the microcomputer.

 

The microcomputer adopts the low-power embedded single-chip microcomputer C8051F007, which has the characteristics of low power supply (2.7 ~ 3.6 V), low power consumption (less than 1 mA), small size (8 mm x 8 mm), and strong function. The microcontroller has 12Bit ADC,35 6BRAM,32kFlash MCU. The microcomputer will collect the pressure signal to analyze, process and memory, eliminate the interference and pressure fluctuation, and send the correct pressure switch status signal.

 

The electronic pressure switch converts the pressure switch status signal of the microcomputer into the guide and disconnection of the intelligent electronic pressure switch.

 

(5) the calibration button in for checking when the smart electron pressure switch, just press the button "calibration" microcomputer memory when the former pressure value automatically, and the value as the smart electron pressure switch setting, so as to realize the intelligent calibration of pressure switch.

 

6 process selection switch, adjacent to the process tank, airtight process can be set different threshold values, the by-pass can process setting threshold value can be appropriately reduced, thus overcome the by-pass can process the problem of pressure switch can't putting-in-service proactively.

 

2.2 key technologies

 

2.2.1 model recognition technology.

 

Oil transfer pump inlet pressure is lower when the impeller cavitation causes the damage of oil transfer pump, so lose station to set pressure regulating system and installed the entrance to the station and pump pressure switch, when pitted low pressure regulation system adjusted first, when the automatic regulation system to adjust station pressure if it continues to fall, after tripping values of the pressure switch will jilt pump so as to achieve the purpose of protecting oil transfer pump. However, the actual operation shows that when the abnormal situation occurs, the automatic regulating system has a lag, and the automatic regulating system does not play the role of the pressure switch. The damage caused by the sudden pumping of the pump is greater than that of the short pump inlet pressure. Reasonable selection is based on the actual situation of the pump station to build the pump inlet pressure to allow the model, the pressure switch is identified according to the model, and decide whether to dump the pump.

 

Taking the luoning line as an example, the pressure regulating system lags about 2 s, and the single stroke of regulating valve is about 9 s. When the abnormal situation is made into the pressure drop of the station, the change curve of the inlet pressure is shown in FIG. 3. The identification model of the pressure switch is as follows: the unit of y: MPa.

 

2.2.2 automatic segmentation of signals.

 

Through the analysis of the field signal many times, the signal automatic segmentation technique and the model recognition technology can be used to effectively overcome various disturbances such as pressure fluctuation and improve the reliability of the pressure switch.

 

Signal, the basic principle of the automatic segmentation method is to choose a fixed window selection signal as a reference of smooth running, constantly compare to the current signal and non-stationary (such as stop pump caused by the change of the signal features) can be made of different period between the statistical characteristics and spectral changes displayed. Generally, according to several criteria, when the criterion is greater than a certain threshold or the current segment is lower than the set value, it is considered that the signal enters another section (abnormal segment).

 

2.2.3 average amplitude distance.

 

The previous signal value.

 

2.2.4 mean square distance.

 

2.2.5 slope mean distance.

 

Length of fitting data segment

 

The slope of the current signal.

 

Kci is the least square fitting slope of xci ~ xc(I +j), and j is the length of fitting data segment.

 

The statistical criteria for the definition of waveform structure are D=aD1+bD2+cD3, in which the weight a, b and c are determined according to the detection requirements and the importance of 3 distances. D and calculated through each Dthres compared threshold value, to determine whether the signal into a new period of (abnormal), at the same time, the current period of less than a given value also determine the signal into a new period of abnormal (section).

 

After the signal enters the new segment, set t=0(to identify the t within the model), start timing and model identification.

 

Identifying criterion B = xc - yt 

 

Yt is calculated by y.

 

For the mean of the current segment signal, the pressure switch action when the criterion B is less than 0. If the criterion B is greater than 0 in the new segment 8 s, the new segment terminates the program into the stable segment.

 

3. Comparison with similar products.

 

The intelligent electronic pressure switch currently has the following characteristics compared with ordinary pressure switches:

 

(1) the model recognition technology is adopted to overcome the instantaneous low pressure of the existing pressure switch.

 

(2) the increased flow switch, adjacent to the process tank, airtight process can be set different threshold, the by-pass can process setting of threshold can be appropriately reduced, so as to solve the by-pass can process the problem of pressure switch can't putting-in-service proactively.

 

(3) to establish the calibration button in for checking when the smart electron pressure switch, just press the button "calibration" microcomputer will be from the current dynamic memory pressure value, and put the value as "intelligent electronic pressure switch Settings, so as to realize the intelligent calibration of pressure switch.

 

4 technical indicators

 

(1) accuracy: 0.002MPa; (2) guide pressure drop: 12V; (3) non-conducting working current: no more than 6mA; (4) system power supply: 24V; (5) environmental temperature: - 10 ~ 50 ℃. (6) withstand pressure: 16MPa.

 

5 conclusion

 

The smart electron pressure switch chose advanced pressure sensor, the model identification and signal automatic segmentation technology, eliminates the pressure fluctuation and other interference, solved the pump caused by automatic regulating system lag. More than one year's field application shows that this intelligent electronic pressure switch technology is advanced, reliable and suitable for oil pipeline.

The above: Connection ways of flow control valve