Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1984-12-21
1986-06-17
Levy, Stewart J.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
G01N 1114
Patent
active
045948836
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method and apparatus for measuring properties of a fluid material within a chamber enclosing impeller means mounted on a stirrer shaft extending into the chamber. In particular, it relates to a method and apparatus for monitoring the properties and flow characteristics of such a material as it is being agitated within a reaction vessel enclosing impeller means mounted on a stirrer shaft extending into the reaction vessel and, optionally, thereby controlling the processes taking place within the vessel.
BACKGROUND ART
Various forms of known apparatus use vibratory methods to measure properties such as viscosity of a material. These all operate on the general principle of bringing the said material into contact with a member, generating and possibly maintaining vibrations on this member by exciting means, detecting the influence of said material on the characteristics of these vibrations and of inferring properties of said material by analysis of this influence on the characteristics of the vibrations. The exciting means for generating and possibly maintaining vibrations do not include the material under test but rather the material only influences the characteristics of vibrations generated by other means and in general these exciting means are located separately from said material. In many cases the material is contained within a sealed chamber and the exciting means are attached to the vibrating member on the outside of the chamber. In general, the vibrations generated on the member by the exciting means are chosen to occur at a limited number of well-defined frequencies. GB-A 1295617 is an example of such known apparatus. Vibrations are induced in a paddle by an electromagnet acting on an arm connected to the paddle by means of a spring and the vibrations induced are detected by a further electromagnet connected to a further arm forming an extension of the first arm on the other side of the spring. The electromagnets and the arms are contained within a sealed housing, the spring extending through a sealable connection to the paddle. The apparatus is designed to operate at the specific natural resonant frequencies of the vibrating system.
Known apparatus as described above is unsuitable for measuring properties of a process material either as it is being agitated within a stirred vessel or as it is being pumped through a pump housing, for two main reasons. Firstly, the vibrating member would be excited, not only by the external means, but also by the flow of the material within the vessel or the pump and this would swamp the vibrations generated by the external means, making it difficult to detect the influence of said material on the characteristics of these externally-generated vibrations, hence making it difficult to infer properties of said material. Secondly, sealing means would be required around the apparatus as it pierces the wall of the vessel or pump and this would be a serious disadvantage in most cases involving materials that are either hazardous or must remain sterile. Known apparatus for use in stirred vessels comprise non-vibratory sensors such as thermometers, pH probes and dissolved-oxygen probes and such sensors are used as a means of monitoring and, optionally, controlling the process more effectively with the aim of improving either the process yield or the quality of the finished product. While these devices may proved adequate within certain process regimes, they may be insensitive to some changes in material properties that have a major influence on yield and product quality. Such non-vibratory sensors also suffer from the drawback of requiring sealing means where they enter a fully-enclosed vessel. Many batch processes within stirred vessels; for example resin manufacture, polymerisation and biotechnology reactions; undergo significant changes in viscosity through the batch and viscometry is therefore a potentially useful means of monitoring and, optionally, controlling the process. However, current techniques for this purpose
Lavine Irvin A.
Levy Stewart J.
Roskos Joseph W.
The British Hydromechanics Research Assoc.
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