The hygienic standards of the food and pharmaceutical industries and the area of medical engineering place special demands on all components used in process automation. This includes the measuring instruments used in these industries, with a particular focus on process connections. They must be certified according to international standards to ensure that no impurities can enter the production process. Two pressure transmitters which fit the bill are from Baumer and they are being successfully used by Swiss-based cleaning and sterilisation specialist Belimed Sauter

The specifications for Baumer’s new product families PBMH and PBMN flush series are based on the company’s experience of the requirements of the food and beverage industries as well as manufacturers of pharmaceuticals. The transmitters are suitable for measuring relative and absolute pressure and can cover measuring ranges from -0.1-0.1 bar through to 0-400 bar. Negative pressures can also be measured.

Hygienic sensors

The need to support many different process connections is not the only challenge posed by hygienic processes. They often cause high temperatures or create hazardous areas. Therefore, the pressure transmitters from the new product families comply with the hygienic norms EHEDG and 3A, and also with the ATEX regulations for use in areas with explosion hazards caused by gas or dust.

As many hygienic processes require particularly rugged sensors, resistance to shocks and vibrations was a focal point in the development of the PBMH and PBMN flush series. Their shock resistance of 100g for 100m/s equals 25 falls onto a concrete floor from a height of one metre. The vibration the devices can resist in operation also complies with high standards and makes it possible to use them in machines in which they are subjected to strong vibration on a long-term basis, such as mills or centrifuges.

The PBMH and PBMN flush series pressure transmitters are actively temperature compensated. Their standard versions can be used for media temperatures of -40 to 125 °C. An optional cooling neck even allows the measuring of media with temperatures of up to 200°C.

The Swiss-based Belimed Sauter AG is an example of a company that has been using Baumer pressure transmitters for years. Belimed Sauter integrated the transmitters into their steam sterilisers for hospitals and laboratories. The company chose Baumer sensors because they are said to provide high accuracy and stability even under the constantly changing extreme temperatures typical for steam sterilisation. One of the key objectives of Baumer’s development team was to ensure these qualities in the new product family to provide customers with long-term investment protection and product support.

Specifications and methods

The efforts in research and development have resulted in all PBMH pressure transmitters having an accuracy of 0.1 per cent F.S. / 0.25 per cent F.S. or 0.5 per cent F.S. (hysteresis, linearity, and repeatability). Their long-term stability amounts to 0.1 per cent F.S. per year. The PBMH pressure transmitters are based on the principle of piezoresistive pressure measurement with silicon measuring cells. This method employs a Wheatstone bridge which is integrated directly into a silicon chip, similar to applications in the semiconductor industry. The chip, covered by a stainless steel casing, is mounted on a standard base. A so-called transfer fluid is used for the pressure transfer from the membrane to the chip.

From the product launch, the new pressure transmitters are available with 11 different types of process connection, a selection of which are 3A-certified. This makes the transmitters compatible not only with all other Baumer products for hygienic applications, but also with the majority of installations from other suppliers in line with the industry standard.

With their cylindrical shape and tube diameter of no more than 22mm, PBMH and PBMN flush transmitters can be used in any application with limited space. Their versatility and the variety of process connections enable users to equip their complete process chain with this product type. This is said to result in advantages not only in terms of user-friendliness, but also with regard to purchase costs since the PBMH and PBMN flush series is said to offer a good price/performance ratio.