Level Measurement & Control


Level sensors shorten the distance from the field to supermarket shelves

August 2021 Level Measurement & Control

Neatly lined up next to each other, the carrots lie packed in trays in the supermarket. A fast, smooth journey from the field to the shelves is now possible because many farming processes, from harvesting to packaging, have been automated. The new compact radar level sensor Vegapuls C 11 plays a decisive role.

The agricultural enterprise Gemüseland Schlereth in Unterpleichfeld keeps an eye on every step of the process, from the harvest to the supermarket shelf. The company started with the cultivation of white cabbage for industrial processing. Since the early 1980s, the farm has specialised in growing fresh vegetables and today, its portfolio ranges from carrots, onions and potatoes to sweetcorn, white and red cabbage and pumpkin, to zucchini, celery, leeks and parsnips.

The products are marketed directly to food retailers with the farm’s own packaging and logistics systems ensuring field-fresh delivery. “Produce is harvested fresh and prepared and delivered to the central warehouses on the same day,” explains Martin Schlereth, who runs the business together with his brother Michael. “The business of agriculture can be challenging as we have to comply with legal requirements like increases in the minimum wage, or stricter measures related to fertiliser ordinance. At the same time, we are feeling the effects of climate change. Higher temperatures, a greater likelihood of severe weather events and longer dry periods are a reality for us farmers today.”

All this must be considered in the harvesting plan and thus already at the time of planting. Farmers also need to rotate crops to ensure that the soil is not depleted and the vegetables retain a consistently high quality.

Automating for the future

However, customers are generally not interested in crop rotation and frost or drought when they make their purchases, they just want visually attractive and tasty carrots. “Customers are placing ever higher demands on quality,” adds Schlereth. “The result is a faster turnover of goods because we have to react to orders placed at ever shorter notice.”

Although the operation can do little about the weather, it has other levers at its disposal. For example, the Schlereth brothers employ state-of-the-art automation to achieve high throughput with consistent product quality. It starts with powerful harvesting machines and tractors and extends to large, modern halls fitted with numerous intelligent packaging machines.

When it comes to level measurement, the company works together with VEGA. “In our biogas plant, which we bought ready to use, there were a number of sensors from VEGA installed,” recalls Schlereth. “Years later, when we redesigned our carrot washing and sorting line, we needed sensors to monitor various levels. VEGA sensors were used there as well.”

Today, VEGA sensors can be found at many different places in the sorting, filling and packaging systems. At centre stage is the compact radar level sensor, Vegapuls C 11.

Plant construction under time pressure

Joachim Hammer, a master electrician from neighbouring Oberpleichfeld, was responsible for the automation. When the planning of the carrot sorting and distribution system started in 2019, he asked VEGA’s field sales staff for help. “The time frame at the time was extremely tight,” explains Hammer. “Planning started in March 2019 and the entire system had to be in place by July. Normally, a processing system like this is built gradually over several months, but this one was built within a week, allowing the carrot processing facility to go into operation on time for the harvest.”

Uniform product flow

“There’s hardly a customer in the supermarket who thinks about the effort that goes into creating a perfect, high-quality package of carrots,” says Schlereth. “At Gemüseland Schlereth, the carrots are brought to the processing plant directly after harvesting. There they are poured into a large washing machine where the coarse dirt is removed. After that, the carrots are transported via conveyor belts to a polishing station and then on to the sorting machines. Here they are sorted according to length and width – some are also rejected – before they are weighed and finally end up in the packaging machines. Several different types of packaging are used for the product. To ensure that the whole plant runs smoothly and that the individual sorting machines and scales work without interruption, the plant is equipped with numerous conveyor belts and switching stations as well as bunkers at strategic locations. This guarantees a steady flow of product through the plant.”

Level measurement is the basis for automation

The entire processing system and especially the speed of the conveyor belts, is controlled by a PLC. This is by no means a trivial task as 60 conveyor belts must be controlled simultaneously. During the automatic transport of vegetables, the height of the goods is measured at transfer stations, switching stations and hoppers.


“At first we tried to measure the product levels with optical methods. Although the ambient conditions do not impose any special requirements, the build-up of dust kept causing problems,” explains Hammer.

The rapid level changes, difficult surfaces, tight conditions and short distances to the medium also challenged the measuring methods that were initially deployed. Yet accurate detection of levels is crucial in order to ultimately achieve a high degree of automation.

The problem was solved by using multiple Vegapuls C 11 sensors, which were installed above the channels, belts and hoppers at distances between one and two metres.

“The fully encapsulated C 11 is robust, which is helpful in view of the damp clay soil around here that sticks to the vegetables,” continues Hammer. “It also delivers reliable, accurate values. Besides being unaffected by temperature or pressures fluctuations, radar sensors are, most importantly, non-sensitive to soiling. What is more, the new Vegapuls series measures with a frequency of 80 GHz, which enables very good signal focusing. With this advanced technology, measurement signals can be better separated from interference and the measuring process thus becomes easier and more precise.”

Another plus point of the sensor is its compact design. The small size is due to the new radar microchip that VEGA designed especially for this sensor series, characterised by compactness and low energy consumption.

Fast set-up

Both the sensors and the controllers can be accessed easily via Bluetooth from a smartphone or tablet. Installation was therefore easy, thanks to the VEGA Tools app. “It’s really easy to use,” says Hammer. “Bluetooth makes everything easier, especially when working in harsh environments or hazardous areas. This was one of the considerations that convinced us of the superiority of VEGA sensors. We were also impressed by the simple, reliable technology, the fast delivery and the prompt response whenever technical advice was needed.”

In 2020, the company also decided to automate the processing and packaging of onions. The facility is a bit smaller than the carrot line – only six Vegapuls C 11 sensors were required – but onions bring even more dirt into the system. For this reason, the sensors must be completely immune to build-up. However, installing the equipment turned out to be somewhat easier. “Onions have to dry anyway, so it doesn’t matter if they lie around for a week longer,” elaborates Hammer. “We thus had a little more time to get the system up and running.”

Although Vegapuls C 11 is interesting in terms of price, this argument alone was not decisive for Hammer: “For me it’s more important to have a reliable contact person who comes to the site from time to time. You see, level measurement is only a small part of the whole system. There’s no way I can know every detail of every sensor, so it’s great to have a supplier that can be reached immediately to answer questions.”

Schlereth agrees: “Communication through our electrician was always good and we especially appreciated the quick and helpful advice we received about the different application possibilities.”

Outlook

The VEGA sensors installed in the facilities for carrot and onion processing have been operating trouble-free from the beginning. Due to past good experiences, Gemüseland Schlereth is now conducting tests with Vegapuls C 11 in the new in-house biogas plant. Until now, pressure transmitters were used there, but the problem is that they are located inside the system components. Servicing them always involves much time-consuming work. “If we could simply use radar sensors to measure from the outside, that would be a great thing for safety reasons alone,” concludes Hammer.

Schlereth is also convinced that, when it comes to modernising a plant or building a new one, you should first contact VEGA if you have questions or need advice about sensors.


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