Application of the hottest ultrasonic level meter

2022-08-08
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The application of ultrasonic level detector in the detection of vacuum treatment silo

[Abstract] this paper introduces the application of the non-contact single probe ultrasonic tension tester of e+h company, which is inconvenient to adopt the vertical structure, in the ferroalloy silo of RH-MFB vacuum treatment device of Panzhihua Iron and Steel Co., Ltd., and expounds the principle, functional characteristics and installation requirements of the detector. Practice has proved that the detector has the advantages of simple installation. 3. Ensuring the smoothness of metal materials, less maintenance, low failure rate, high accuracy (its resolution is within ± 5mm), simple calibration, safety and reliability, and has the value of promotion

[key words] level measurement; Non contact type; ultrasonic; Matrix

[Chinese library classification number]tp274.53 [document identification code]b [article number) 1000-0682 (2004)

1 introduction

Panzhihua Iron and steel RH-MFB vacuum treatment device mainly removes gas, inclusions, desulfurization and decarbonization from molten steel. During the treatment process, alloy needs to be added to adjust the composition of molten steel, so 14 alloy silos are set. In order to master the amount of alloy level in the silo and control the alloy addition speed in time, it is necessary to detect the alloy level. Because the measured medium in the silo is rough and loose solid, among various level detection instruments, the ultrasonic level detector has non-contact, corrosion-resistant, suitable for the height measurement of materials in large storage tanks, and can correct the factors affecting the measurement accuracy and output various standard signals according to user requirements. It has been widely used in the production process. Therefore, the non-contact single probe ultrasonic level detector of e+h company is selected

2 ultrasonic testing principle

the high-power piezoelectric ceramic ultrasonic probe emits focused ultrasonic pulses, which pass through the air to the surface of the measured medium, and the pulses are fully or partially reflected back to the probe. The probe is both a transmitting device and a receiving device, which converts the received reflected wave into an electrical signal. According to the fact that the time of sending and receiving the pulse is proportional to the distance between the probe and the medium surface, the distance D can be calculated by the following formula:

d=c · T/2 (2-1)

C - sound speed; T -- sound wave transmission time

set the distance between the probe and the lower part of the silo as B, then the silo height h is: h=l-d=l-d=l-c · T/2, as shown in Figure 2-1. B is the blind area

since the temperature change has a great impact on the sound speed C, the sound speed must be compensated through the temperature sensor and its compensation circuit. Compensation can be carried out according to the following formula; C=331.45+0.61t, each time the detection system measures time t, at the same time, the factory value of temperature is used, and then the sound velocity C is calculated according to the above formula, which is brought into formula (2-1) to calculate distance D

3 system composition and functional characteristics

composition of ultrasonic detection system: ultrasonic probe du41c, material level transmitter fmu677, communicator uv260z. 14 sets of ultrasonic testing systems are set in 14 silos. The transmitter adopts bracket installation, uses shielded cable, and the output signal is used as the analog input of Siemens plcs5-155u. The relay contact signal is connected with the digital input module of PLC. It has high and low limit alarm function, and the detection results are displayed on the operation station. The composition is shown in Figure 2-1

3.1 ultrasonic probe

the probe model is du41c, corrosion-resistant, with automatic echo frequency control, suitable for continuous, non-contact level measurement. The working temperature is - 20 ℃ ~+60 ℃. In order to compensate the error caused by temperature change, a temperature probe is also installed in the ultrasonic probe to correct the temperature change. The probe can measure 20m deep liquid level and 10m high loose solid level. The working frequency is about 29khz, and the blind area is about 0.9m

3.2 ultrasonic transmitter

transmitter fmu677 is used as the process variable of the control system to detect the level of the silo. The transmitter supplies power to the probe, and the probe sends back the analog signal of the measured value. The transmitter converts this signal into material level indication and sends it to the analog output end

all functions of the transmitter, including analog output, relay conversion point and other parameters, can be configured and input with the help of the work matrix table. Each value in the matrix is displayed in vertical (V) and horizontal (H) coordinates. For measurement points and system calibration, the working matrix must be called. Fault diagnosis information can also be found in the matrix table. It can be input in the front panel of the transmitter with the help of communicator uv260z, which is easy to operate. The measuring system has six working modes, making it suitable for measuring liquids or loose solids. The measured medium of the system is rough loose solid, so working mode 5 is selected. For containers whose volume is not proportional to the material level, manual linearization can convert the material level measurement into volume measurement

the analog output of the transmitter has one convertible current output of 0 (or 4) ~20ma and the other convertible voltage output of 0 (or 2) ~10v. Internal filters are used to smooth analog output fluctuations. If a fault or alarm is found in the self tracking line of the transmitter, the current and voltage output can adopt specific values, and at this time, the relay acts with the high and low limits of the analog output. Two independent relays of the transmitter, each with voltage isolation, conduct contact conversion according to the measured value. Each limit switch can adopt the minimum/maximum fault safety mode, and the delay time of the limit switch can be freely selected, which is the point when the relay is disconnected when the material level returns to normal

for potential or intermittent echo interference inside the noise tolerant and pollution-free device, fixed target suppression can be adopted to prevent false echo; Or envelope curve statistics, calculate the average value of all envelope curves, and adjust appropriate parameters to suppress intermittent interference; If there is a fixed part between the maximum material level and the blind area, increasing the blind area distance can eliminate the echo generated by it

in addition, the transmitter can monitor all circuits from the probe to the output and indicate the fault signal sent by the alarm relay (the alarm light is on and the fault signal is transmitted). In addition, the simulation method can be used to check whether the system operates normally, which is conducive to the timely and accurate troubleshooting of staff

3.3 installation requirements

an important prerequisite for accurate ultrasonic measurement is the correct positioning and installation of the probe, so that the detector can be used normally and the measurement error can be reduced. Pay attention to the following points during installation:

1) during installation, it should be perpendicular to the surface of the medium, leaving a blind area, and the medium will not contact the probe when the container overflows

2) when measuring the solid material level elbow in the silo, it should be considered that the solid material is not flat on the interface. Generally, the material at the feed inlet is higher than the surrounding of the storage bin, so the probe should be installed at the position where the average height of the reaction material can be measured, and the probe should not be installed at the center of the top of the silo. PEUU and PCU research shows that

3) the ultrasonic probe has its sound wave pointing angle. Any object within the range of the transmitted beam, including the walls of containers and storage tanks, will reflect interference echoes and generate measurement errors, so the installation position of the probe should not be too close to the wall. In practical application, because the lower part of the silo is conical, sound waves will also be reflected near the center of the material outlet funnel (even if the hopper is empty), so adjust the angle of the probe to be as far away from the container wall, baffle and material inlet as possible

4 conclusion

the ultrasonic level detector has operated normally since it was put into operation (the measurement resolution is within ± 5mm), and has achieved great economic benefits, which is worthy of popularization and application. Its advantages are mainly reflected in the following aspects:

because the ultrasonic level meter has no movable parts, no mechanical wear, simple installation and easy implementation; Less non-contact measurement and maintenance, reducing the failure rate; Calibration is simple, high precision, safe and reliable

the upper and lower limit alarms of the system are accurate, ensuring the timely addition and reduction of materials; Accurate measurement and intuitive display enable operators to effectively control the alloy addition speed, improve work efficiency and accuracy, and create conditions for continuous casting to produce high-quality alloy steel

[References]

[1] Wang Jue, Jiao Qing, Shen Yi, research on the application of new level detection technology

[J]. Industrial instruments and automation devices, 2002, (1): 15-18.

author's profile: Song Dongfei (1971-), male, Han, Henan Dengzhou, engineer, mainly engaged in thermal instrument automation and computer control technology

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