Example of limestone slurry measurement with ultrasonic level gauge

Application of ultrasonic level gauge in limestone slurry measurement

 

As a non-contact liquid level measuring instrument, ultrasonic level gauge has the advantages of simple structure, easy installation and commissioning, and small maintenance workload, and can observe the liquid level in real time in the control room and the field, and has a wide range of applications in the measurement of various liquid levels. It mainly emits ultrasonic pulses through the probe (also known as transducer), and when the pulse touches the media interface, it is reflected back and received by the probe. Based on the time it takes for the pulse to be transmitted from transmission to reception and the speed of sound propagating through the medium, the distance between the probe and the medium can be determined to determine where the liquid is located. However, in practical applications, due to the difference in installation position and installation method, it may lead to the phenomenon that the ultrasonic level gauge cannot work properly. In this paper, the application of ultrasonic level gauge in limestone slurry measurement is described as follows.

First, the application overview

In May this year, a large state-owned chemical company in northern China purchased a batch of liquid level dry peak ultrasonic level gauges for measuring and monitoring sewage water levels and limestone slurry. According to user feedback, during use, the indicators of the ultrasonic level gauge for measuring the sewage water level are all normal, and the measurement is accurate and reliable. However, the other two ultrasonic level gauges used to measure limestone slurry are not able to measure accurately, and the data fluctuates greatly during the measurement process, and the measurement data does not match the actual liquid level height.

After receiving the feedback from the user, Qianfeng Vaillant Instrument immediately arranged technical engineers to go to the site to understand the situation and provide technical support. At the application site, Qianfeng engineers saw exactly the same situation as the customer described, but with rich experience, the engineers found that the problem of inaccurate on-site measurement was not caused by product quality. So what is the reason for this?

2. Problem analysis

 

 

After the investigation and analysis of Qianfeng engineers, it was found that there are three main reasons why the ultrasonic level gauge cannot be accurately measured in the limestone slurry measurement: 1.

There is a stirring device

on site In some liquid level measurement environments with stirring or more dynamic (such as fluids), due to the dynamic fluctuations and uncertain changes of the liquid level, the energy recovery of the ultrasonic level gauge is disturbed. This affects the measurement accuracy of the ultrasonic level gauge.

2. The installation position of the ultrasonic level gauge is close
to the tank wall, and the emission angle of
the ultrasonic level gauge probe is 8~12°. When the installation position is close to the tank wall, the energy recovery is susceptible to interference due to the influence of the emission angle, which affects the accuracy of the measurement.

3. The ultrasonic level gauge is not equipped with a protective retaining box
The calculation formula of the
ultrasonic level gauge level measurement is S=C×T/2, which reflects the relationship between the distance value S and the sound velocity C and the transmission time T. According to the formula, in order to measure the liquid level by using the ultrasonic level gauge, it is necessary to know the ultrasonic propagation velocity in the air, and it can be said that the accuracy of the ultrasonic propagation velocity will greatly affect the measurement accuracy of the ultrasonic level gauge, and the formula is as follows:

c=(331.45+0.61t/°C)m/s

The temperature sensor of the ultrasonic level gauge is encapsulated in a protective material as part of the probe, and it can be seen from the formula that temperature is the main factor affecting the speed of sound. If the ultrasonic level gauge is installed in an unobstructed outdoor environment, the exposure of sunlight will make the shell and probe of the ultrasonic level gauge continue to heat up, and the ambient temperature will not continue to heat up like the probe, and the temperature measured by the sensor in the final probe is quite different from the temperature of the environment, which affects the accuracy of the measurement.

In the north, where the summer is hot and dry, and the winter is extremely cold, the ultrasonic level gauge placed outdoors is easily affected by drastic temperature changes, which can cause changes in sound speed and cause measurement errors. In this case, an ultrasonic level gauge can be fitted with a protective retainer to reduce the effects of sudden temperature changes. At the same time, a temperature sensor is installed on the ultrasonic level gauge to measure the temperature in real time, and the sound velocity value can be converted by using the relationship between temperature and sound velocity.

3. Countermeasures

 

 

In view of the above problems and reasons, in order to solve the problem of inaccurate measurement of ultrasonic level gauge in limestone slurry, there are the following specific solutions to choose from: 1.

The ultrasonic level gauge should be installed
60cm away from the tank wall
Since the user chooses an ultrasonic level gauge with a range of 10 meters, the emission angle of the ultrasonic level gauge probe is 10°. The installation position of the ultrasonic level gauge should be 60cm away from the tank wall.

2. Install a protective cover

Because it is located outdoors, it is difficult to avoid being exposed to the sun and rain, at this time, install a protective cover for the instrument, so that the ultrasonic level gauge is protected from the influence of temperature changes caused by sun and rain on the sound velocity, so that the measurement is more accurate.

3. Install the waveguide tube

By installing the waveguide, the ultrasonic pulse emitted by the ultrasonic level gauge can be kept away from the stirring radius, and the liquid level with small fluctuations can be aligned, so as to minimize the interference of the ultrasonic level gauge energy recovery by the fluctuation of the liquid level, so as to achieve accurate measurement.

In the actual installation process, there are generally two installation methods shown in Figure 2, one is to install the waveguide tube outside the storage tank, and the other is to install the waveguide tube in the storage tank, and the diameter of the waveguide tube usually needs to be more than 100mm.

By taking the above-mentioned targeted measures, the problems existing in the user's application are satisfactorily solved. After the reinstallation, the ultrasonic level gauge no longer had the same problems as before.

Fourth, the characteristics of the dry peak ultrasonic level gauge
Due to many innovations and improvements, compared with the traditional ultrasonic level gauge, the dry peak ultrasonic level gauge has its own characteristics and advantages:

 

 

1. Software and hardware upgrades. In view of the large on-site fluctuations in the industrial site, Shenyang Qianfeng Automation has improved the robustness of the instrument (robustness is roughly equivalent to stability) in hardware and software. In terms of software, the addition of the delay average algorithm can make the instrument better adapt to complex and changeable working conditions; In terms of hardware, an efficient and rigorous signal filtering circuit is adopted to filter out the secondary waves and clutter generated by the ultrasonic signal contacting the liquid level during the level measurement.

2. With temperature compensation function, it can be used in an environment with large temperature difference, strong adaptability and high measurement accuracy.

3. Good sealing. The protection level of the ultrasonic level gauge is up to IP68;

4. It has RS-485 communication interface and adopts special echo processing mode, so that the false echo phenomenon can be effectively avoided.

The ultrasonic level gauge developed and produced by Shenyang Qianfeng has the characteristics of high measurement accuracy, stability and reliability, and is widely used in different industrial environments, smart cities and sewage treatment.