Only the best for man's best friend

In the production of dog food pellets, the manufacturer struggled constantly with an unreliable measuring point. After several different measuring principles failed, a breakthrough was achieved with 80-GHz radar level measurement technology, explains Dipl.-Ing. Sabine Mühlenkamp, specialised journalist for the chemical industry and general technology.

The dog is one of man’s favourite companions. Many dog owners spare no effort in care and want only the very best for their pet. Accordingly, a wide range of dog food is available, from puppy food to senior mixes, as well as products for stomach-sensitive and allergic animals. The product range and the variety of recipes has been growing for years.

Image credit: Vega

The South African company RCL Foods knows exactly what dogs like to eat. This leading African food producer, with over 20,000 employees in subsidiaries in South Africa, Swaziland, Namibia, Botswana and Zambia, not only produces various types of pet food, but has also developed and designed its own production equipment for just that purpose. Yet adding essential oils and fats to the food products has proven to be a very difficult and complex process.

Step by step to the pellet

The basic steps of the pet food process include sourcing raw materials, commingling via a dosing system that involves adding essential vitamins and nutrients, grinding to a specific specification and size, and then mixing. In the next step, the pre-processed product is fed pneumatically via a conveyor line to the extrusion unit. Steam, water and other ingredients are added there to produce many different shapes, sizes and mixes of animal feed.

After extrusion, the product must be dried according to moisture specifications. When the product leaves the dryer, it gets coated with essential fats and oils. At this point in the process, however, there have always been difficulties until now. Although this brand new, state-of-the-art facility was designed and built by the company’s own engineering team, one measuring point did not provide readings reliable enough to ensure a smooth, continuous process. The problem: When the product leaves the batch dryer, the food product is supplied with fats and oils. For this purpose a container for holding the dried pellets was installed. This in turn feeds a belt weigher, which is used to obtain an accurate flow rate for the addition of fats and oils. It is absolutely necessary for the filling level in this storage container to be reliably measured in order to achieve an unvarying flow.

Image credit: Vega

A roundabout way to the goal

At first glance, the measuring point does not appear to be especially problematic. The ambient temperature is moderate and the food pellets are actually easy to handle. From time-to-time light vibration occurs in the system, but that normally does not affect the measurement.

So, the company tried out a whole range of different level sensors. First, they used a guided radar level gauge from another manufacturer. However, the return signal was always received with a delay, even when the signal damping parameter was set to zero. The next measuring principle that was tried out was the laser − a measuring device that basically operates according to the same functional principle as an ultrasonic level sensor. This solution was not satisfactory either.

A breakthrough thanks to 80 GHz

RCL has been working with Vega for more than a decade and appreciates the excellent service provided by the local subsidiary of the Black Forest company. It also considers the dependability and high quality of Vega instruments unrivalled. For that reason, RCL placed great trust in the Vega team, but at first did not have high hopes that there could be a solution for this difficult measuring situation. Vega proposed a trial run with VEGAPULS, a radar level transmitter that was still quite new at the time. The higher, 80-GHz frequency considerably extended the spectrum of applications for radar level measurement technology. An essential aspect of this success is the fact that the measuring instrument only requires an opening angle of 3° (previously 10°), which allows the measuring beam to glide right past internal fixtures or build-up on the vessel wall. In practice, the significantly tighter focusing of the transmitted signal offers a whole range of advantages, the most important being that the actual measuring signal can be better separated from interference signals, allowing even the smallest reflection signals to be detected.


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