Performing Flow Measurements with the Ultrasound Transit Time Method

Table of Contents

Introduction
Decision-Maker Facts for Operators
Process Sensor Technology
Documented Quality
Requirements for the Flow Measurement
Previous Measurement Methods

Introduction

Operators are capable of performing flow measurements with the ultrasound method, without making any contact with the medium. The method is appropriate, for instance, if users have to weed media without causing danger to their hygiene.

Decision-Maker Facts for Operators

  • In the hygiene field, operators often work with processes where precise dosing of the beginning and intermediate materials is important, for the process itself as well as for profitability. The substances employed are often very expensive.
  • The measurements needed for this can be performed by operators using several methods, but these are often affected by several disadvantages. The measurement method highlighted in this article clears up all disadvantages.

Process Sensor Technology

In liquid-based manufacturing techniques, it has a greater importance: the process sensor technology. For instance, it is employed in fermentation, in beverage production and mixing, or in processes with microorganisms. Particularly in the case of outgoing and incoming liquid systems which passively or actively impact the flow through valves or pumps, a constant disturbance monitoring of hose systems for occlusion or idling, the control of the conveyed flow or the observation of applied or removed liquid quantities in the aseptic production process plays a significant role. The precise dosing of the partly high-grade starting or intermediate products is crucial, because these have a great impact on the quality or the adherence to a reliable product formulation. In addition, a process-safe economic method of production is not an insignificant aspect.

Flow Measurements with the Ultrasound Transit Time Method

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

Documented Quality

With the flow sensors appropriate for the particular application conditions, an automated process control by the control of vales or pumps can precisely control the flow. Thus, critical process steps can be precisely monitored and documented, denoting that operators obtain long-term competitive advantages.

Additionally, it meets the requirements of "good manufacturing practice" (GMP / cGMP), which is required in many areas of pharmaceutical and food production. The measurement of flow rates is required at different points in the process sequence, whether at the time of preparation or mixing of the formulations with raw materials, buffer solutions or in successive refining steps, for instance, the concentration of media through membrane filters or in the case of chromatography applications. Liquids are delivered through pipes and through a wide range of flexible hose types. Specifically, in processes with high requirements regarding sterility and hygiene, the cleaning of stainless steel tubes is, for instance, very expensive to achieve the required purity. As far as possible, flexible tubing systems are often employed for single use, because the stringent requirements are thus easier to fulfill and with less expense and time for the user.

Requirements for the Flow Measurement

There are many different processes to measure a volume flow of liquids and these processes are relatively suitable for use in the pharmaceutical and food industries. Since very high flow measurement requirements are needed, this must be precise and have a high measuring range at high resolution and little interference with the actual process. For instance, this is normally performed without an increase in dead volumes and without media contact. If pumps are used, users can adjust the volume flow simply, but indirectly, depending on the speed or the required electrical energy. It is not required to use additional measuring equipment. Since this is particularly possible with a comparatively high inaccuracy in the regularly used roller pumps, it needs a permanent recalibration, because they roll out the hose unevenly. Also in the case of centrifugal pumps, there is a backpressure dependency of the produced flow, which cannot be estimated correctly from the pump load.

Flow Measurements with the Ultrasound Transit Time Method

The method allows reliable flow measurement.

Previous Measurement Methods

An additional indirect possibility to measure flow rates is to use scales on containers, provided that the density is known. Generally, scales are very precise measuring instruments; however, there are also many disadvantages. On the one hand, just the weight change of a complete reactor vessel or container can be determined, that is, media fed in parallel normally cannot be determined without further; except these would always be added one after the other. In addition, the dynamics of the measuring range of the balance should be designed for the total weight of the container, including the coupled straining elements, such as stirrers, holders for additional small containers etc., at the expense of the resolution.

The calibration of the mechanical scales should be checked regularly, and mechanically poor constructions and ambient conditions can affect the measuring result and hamper the integration. Particularly when huge containers are pumped into the company, the space required 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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