Product category:
Level and tank contents instrumentation
News Release from: Endress + Hauser | Subject: Radar tank level measurement
Edited by the Processingtalk Editorial
Team on 02 September 2005
Trends in radar level measurement
Over the past few years, the performance and variety of level radar devices has significantly increased: the following review discusses the different aspects of process tank applications
Over the past few years, the performance and variety of level radar devices has significantly increased In industrial measurement engineering, continuous level monitoring of liquids plays an important role
This article was originally published on Processingtalk on 26 Jun 2008 at 8.00am (UK)
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The trend has shifted to non-contact methods, in particular the 'Time of Flight' radar principle.
The low cost of ownership of these methods was attributed to their fundamental technical advantages, ie no moving parts, no immediate contact with the media/products etc.
Initially, radar level measurement established itself in high-precision tank gauging applications, with extremely predictable process conditions.
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The situation was different in process measurement, high expectations were not borne out by performance and the positive image of this technique began to fade.
Several factors were responsible.
* Incorrect specification.
* Insufficient understanding of the limitations of radar.
* Over estimation of the potential of the product from a manufacturer's perspective.
All these factors contributed to a decline in end user confidence in radar measurement.
Today, lessons have been learned.
Investment in product development has brought significant improvement in performance and operation.
The trend is towards smaller, lighter and more cost-effective systems in the area of high-precision level applications.
For the first time, measurements exact to the millimetre can be attained using pulsed techniques: for example, the Endress+Hauser Micropilot S.
Apart from the obvious characteristics, like temperature, pressure and the dielectric constant, the condition of the product surface is the most important application parameter in high-precision systems.
In addition, different tank geometries have to be considered.
Applications may thus be classified in accordance with these primary criteria.
Storage tanks.
Storage tanks have very calm and predictable surfaces, since they are filled near the bottom or employ immersion tubes.
An additional challenge is often constituted by the relatively small nozzles, sometimes only a short distance from the wall.
Buffer tanks.
Buffer tanks are usually filled from above, from the side or the product is injected via jets causing surface disturbance.
The formation of foam and splashing constitute further demands on level measurement.
An accuracy of +/-10mm is sufficient in normal operation for such applications.
Agitated tanks.
Tanks that incorporate agitators can suffer from strong turbulence.
In addition, the agitator blades may cross the radar beam during measurement and the resulting interference signals have to be suppressed.
Accuracy requirements are lower, but the reliability of the measurement is particularly important.
Stilling wells and bypass chambers.
Radar level systems are now commonplace in tank gauging applications and many use stilling wells with holes and slots often unevenly distributed.
In process applications, displacers and floats are being replaced by radar systems returning an accuracy of +/-3mm.
For products with low dielectric constants (<2) both bypass and stilling wells act as waveguides, ensuring reliable measurement.
In comparison to the instrument features, the significance of antenna technology is often underestimated.
Safety properties like a gas-tight feed-through second line of defence in the measurement of toxic media, and the conductivity of the antenna - particularly for PTFE antennae - protecting against static load are also important to the user.
Furthermore, the absence of seals, corrosion resistance and the choice of materials play a significant part in attaining the required approvals.
In aggressive media, for example, fully PTFE-coated rod antennae without any seal in contact with the process are recommended and have even received the FDA/3A approval for hygienic and pharmaceutical process requirements.
Enamelled horn antennae provide an alternative solution in this respect.
New developments have focused on ease of use and maintenance requirements.
Uniform tools for commissioning and diagnostics are now standard features and the need for application-specific documentation has also been addressed.
The Endress+Hauser Micropilot M takes users, step by step, through the process.
It features a 4-line clear text display, offering simple, menu-driven commissioning.
This review is provided by Dr Michael Heim and Dr Andreas Mayr, of Endress+Hauser. Request a free brochure from Endress + Hauser ...
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