Online level measurementPrefaceWith the improvement of the level of automation in flour processing plants, on-site inspection of the production process and selection of scientific control instruments are becoming more and more important.The processing process of the flour processing factory includes: after the raw wheat is transported to the factory, it is cleaned, moistened (stored for 24 hours), and then transported to the processing workshop for processing (including peeling and grinding). After the wheat is peeled, it is ground into flour and transported to the flour storage bin for storage or packaging. Tempering silos, flour silos and temporary packaging hoppers all need to control the material level to ensure the efficient operation of production.At present, the domestic flour mills have selected various brands of level switch, and the quality is uneven. Level false alarms and production shutdowns caused by level switch failures occur from time to time. How to choose the level switch scientifically and reasonably has become a common problem in the industry. Through the comparison and analysis of the specific requirements of the application conditions of the flour mill and the main level switches at home and abroad, it provides help and reference for the selection of the level switch of the flour mill.Current status of level switch application technologyAt present, the most used level switches for raw material warehouses (wheat) and finished product warehouses (flour) in flour mills are anti-rotation level switches and radio frequency admittance level switches. In a few cases, radar level meters and ultrasonic level switches are also used.Because of its low price and simple installation, it was favored by many manufacturers in the early days. However, many manufacturers find that their motors are easily damaged after using the anti-rotation material level switch, resulting in failure to operate normally, affecting production efficiency, and even unable to produce; in addition, due to the lubricating moving parts, it is easy to supply raw material warehouses, wheat silo, and finished product warehouses. The materials cause pollution and cause economic losses. Because the humidity of wheat and flour are different after wetting, the dielectric constant will often change, which easily leads to the abnormal use of the radio frequency admittance level switch; in addition, the probe of the radio frequency admittance level switch is embedded (slender), It is easy to cause the probe to bend or break, cause damage to the radio frequency admittance level switch, and affect normal production.Although the radar level gauge has a good measurement effect in the raw material warehouse, it is expensive and cost-effective. The price of the ultrasonic level gauge is reasonable. However, due to the large dust in the flour mill, the measurement in the finished product warehouse is often inaccurate and false alarms often occur. In the level measurement of flour mills, how to choose the level switch reasonably, ensure the safe and reliable storage of materials, and ensure continuous and stable production, has become an urgent problem for the flour mill.Technical selection requirements for level switchesIn order to ensure the long-term, high-efficiency, safe and stable operation of the automatic production of the flour processing plant, improve production efficiency, save labor costs, and maximize the economic benefits of the flour processing plant.Combined with the actual production process of the flour mill, the selection of the level switch should meet the following requirements:(1) Food gradeBecause flour is related to people’s health, in order to avoid secondary pollution to raw material warehouses, wheat silo, finished product warehouse and other materials. The selection of the level switch must meet the food grade, that is, the product cannot have lubricated moving parts, the probe is made of at least 304 stainless steel, and the surface finish should be less than 0.8 m(2) High reliabilityFlour processing technology includes raw grain receiving, storage and cleaning, wheat flour milling, flour post-processing, packaging, storage and distribution of finished products and by-products. The working conditions are complex, and the selection of the level switch must meet the high reliability requirements of no false alarm, anti-interference, anti-hanging, strong performance, and long service life.(3) Dust explosion-proofDuring the flour production process, a large amount of dust is generated. When dust is suspended in the air and reaches an explosive concentration, it will burn immediately under the conditions of flame, spark, arc or appropriate temperature, forming a violent explosion. Therefore, the selection of the level switch must meet the requirements of dust explosion-proof to ensure the safe production of the factory.(4) Easy to installIn order to reduce the later installation and debugging time and maintenance costs, and improve construction efficiency, easy-to-install and maintenance-free measurement schemes should be considered when selecting models.(5) High cost performanceWhen the above requirements are met, price will be an important reference factor affecting product selection. Due to the high price of radar level gauges, the cost performance is extremely low.Performance comparison of main level switches at home and abroadDifferent material level measuring instruments are used to measure different materials and different working conditions. The main level measuring instruments at home and abroad include: anti-rotation level switch, tuning fork level switch, radio frequency admittance level switch, radar level meter, vibrating rod level switch, etc.Due to the different principles, the performance of the level measuring instrument is also different, so it is very important to choose the best measuring instrument in actual production.(1) Rotary resistance level switchBecause the anti-rotation level switch has lubricated moving parts, it cannot meet the food-grade requirements of flour mills.(2) Tuning fork level switchWhen measuring powdery materials, domestic ordinary tuning fork level switches are easy to perforate and cause false alarms. Therefore, domestic ordinary tuning fork level switches are not suitable for use in flour mills.(3) RF admittance level switchDue to structural design, the radio frequency admittance level switch cannot meet the requirements of dust explosion-proof.(4) Single material position switchIt is often used in food processing, but due to its single-pole structure, it has poor anti-hanging ability and is prone to false alarms. The price is not cheap and the cost performance is not high.(5) Double lever material position switchThe double rod vibrating rod material level switch overcomes the shortcomings of the single rod material level switch’s poor anti-hanging ability, and the work is more stable and reliable. At the same time, the circuit and structure design can meet the requirements of dust explosion-proof, which is very suitable for the material metering of flour mills. Please refer to the table below for the performance comparison of different levels of switches.Performance comparison table of different level switchesFrom the performance comparison of different level switches in the above table, it is not difficult to see that the double-bar level switch is the most suitable level measuring instrument for flour mills. At present, the imported double-row material level switch is expensive and low cost performance, while the domestic double-row material level switch is reasonably priced, and its performance is equivalent to that of foreign double-row material level switches.Since 2017, COFCO has installed 36 sets of Shenzhen Huikeda Automation Technology Co., Ltd. Long Tube-11 double-rod vibrating bar level switches in raw material warehouses and finished product warehouses to replace the previously used anti-rotation level switches. The double-rod vibrating bar material level switch has been stable and reliable since its use, and it has solved the problems of complicated installation and debugging, easy false alarms, easy bending of the probe, digging phenomenon and short service life of other level switches used in flour mills. Get rid of the trouble of repeated interruptions in production, save labor costs, and improve production efficiency. Huikeda tube-11 double rod vibrating rod material level switch telescopic tubeConcluding remarks
This paper systematically describes the application status and existing problems of liquid level switches in flour mills, compares the performance characteristics and advantages and disadvantages of various liquid level switches, provides a reference for the selection of liquid level switches in flour mills, and ensures the long-term, long-term, automatic production of flour mills. Efficient, safe and stable operation, to minimize financial and human losses, and maximize the economic benefits of the flour mill.
Post time: 21-09-21