Ultrasound Transit Time Method and Flow Measurements

Operators can perform flow measurements with the ultrasound method, without making any contact with the medium. The method is suitable in instances where users have to weed media without compromising on their hygiene.

Decision-Maker Facts for Operators

  • In the hygiene field, operators frequently work with processes where precise dosing of the beginning and intermediate materials is essential, for both the process itself and profitability. The substances used are often very expensive.
  • The measurements required for this can be carried out by operators using several methods, but these are usually affected by several disadvantages. The measurement method highlighted in this article resolves all disadvantages.

Process Sensor Technology

The process sensor technology has a greater importance in liquid-based manufacturing techniques. For example, it is used in beverage production and mixing, in fermentation, or in processes with microorganisms. Specifically in the case of incoming and outgoing liquid systems which actively or passively affect the flow through pumps or valves, a constant disturbance monitoring of hose systems for idling or occlusion, the control of the conveyed flow, or the observation of applied or removed liquid quantities in the aseptic production process plays a major role. The precise dosing of the partially high-grade starting or intermediate products is critical, as these greatly influence the quality or the adherence to a dependable product formulation. Besides this, a process-safe economic method of production is a significant aspect.

Liquids are measured by the system without contact with the medium or product by ultrasound.

Liquids are measured by the system without contact with the medium or product by ultrasound.

Documented Quality

With the flow sensors suitable for the specific application conditions, an automated process control through the control of pumps or valves can precisely control the flow. Hence, critical process steps can be precisely monitored and documented, indicating that operators achieve long-term competitive advantages.

It also meets the requirements of "good manufacturing practice" (GMP / cGMP), which is necessary in many areas of food and pharmaceutical production. There is a need to measure the flow rates at different points in the process sequence, be it at the time of preparation or mixing of the formulations with buffer solutions, raw materials or in successive refining steps, for example, the concentration of media through membrane filters or in the case of chromatography applications. Pipes and a wide array of flexible hose types are used to deliver liquids.

Particularly, in processes demanding high levels of hygiene and sterility, the cleaning of stainless steel tubes is, for example, very expensive to attain the necessary purity. As much as possible, flexible tubing systems are typically used for just one use, because it is easier to meet the stringent requirements this way and with less time and expense for the user.

Requirements for the Flow Measurement

There are various processes to measure a volume flow of liquids and these processes are quite suitable for use in the food and pharmaceutical industries. Considering the need for very high flow measurement requirements, this must be precise and have a high measuring range at high resolution and little interference with the actual process. For example, this is usually carried out without an increase in dead volumes and without media contact. If pumps are used, users can adjust the volume flow easily, but indirectly, based on the speed or the required electrical energy.

There is no need to use additional measuring equipment. As this is especially possible with a comparatively high inaccuracy in the regularly used roller pumps, it requires a permanent recalibration, because they roll out the hose unevenly. Also, with regards to centrifugal pumps, there is a backpressure dependency of the produced flow, which cannot be accurately estimated from the pump load.

flow measurement

The method allows reliable flow measurement.

Previous Measurement Methods

Another indirect possibility to measure flow rates is to use scales on containers, provided that the density is known. Normally, scales are highly precise measuring instruments; though, there are also several disadvantages. On the one hand, only the weight change of a complete reactor vessel or container can be established, that is, media fed in parallel cannot be determined further; except these would invariably be added one after the other. Furthermore, the dynamics of the measuring range of the balance should be designed for the total weight of the container, including the coupled straining elements, for example stirrers, holders for additional small containers etc., at the cost of the resolution.

It is important to check the calibration of the mechanical scales regularly, plus ambient conditions and mechanically poor constructions can affect the measuring result and hamper the integration. In particular, when huge containers are pumped into the company, the space needed for the weighing mechanism also becomes large.

em-tec GmbH.

This information has been sourced, reviewed and adapted from materials provided by em-tec GmbH.

For more information on this source, please visit em-tec GmbH.

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