Thursday 25 March 2010

Direct on-line measurement of density and concentration

Eliminates the need for expensive laboratory analysis.

Endress+Hauser has introduced the Liquiphant M, a density meter that provides on-line measurements, eliminating the need for extensive and expensive off-line procedures and laboratory measurements. A built-in density calculator can be end user customized with complex tables and mathematical interdependencies, allowing the meter to provide the same kind of density and concentration measurements once possible only with lab instruments.

Because the Liquiphant M provides on-line measurements, it allows control systems to react much faster to changing process conditions. Instead of waiting for results to come back from the lab, a control system can take corrective action immediately by performing closed-loop control.

Calculating Density
The Liquiphant employs a mechanically oscillating fork with two tines that are each excited to resonant frequency. The frequency changes when the fork is immersed in any liquid. If the vibration falls below a predetermined frequency, the sensor reports the covered state to a subsequent switching electronics. The tines are excited by a piezoelectric drive. The resonant frequency depends on the moment of inertia of the fork as well as the membrane stiffness, and the frequency measures approximately 1000-1200Hz in air.

Changes in resonant frequency are directly interrelated with the density of the medium. In a lower medium density, such as liquefied gas, the resulting resonant frequency is higher than in more pronounced densities like water. The electronics of the Liquiphant can measure this change in the resonant frequency. The density of the medium can also be calculated taking temperature and process pressure into consideration.

Concentration can be calculated in mass or volume units. For example, "Degree Brix" is a measuring unit for the specific density of liquids. This is particularly used in the food industry to determine the sugar content in fruit juices and beverages, or in oil production to measure the salt concentration in tanks.

The customer can customize the Liquiphant M for many density and concentration applications including but not limited to:
  • Content measurement and concentration (sulphuric acid, sugar, alcohol, etc.)
  • Quality statements (mineral oil, milk, etc.)
  • Purity indication
  • Product identification
  • As a changing variable indicating the metabolism in relation to kinetic statements (reaction rate)
  • As a basic variable for physical calculations or simulations
  • For clarification of how much material is contained in a given volume.
The Liquiphant M Density meter is capable of providing analytical process information on-line and in-line according to customer requirements. It offers solutions for a variety of applications including process optimization, quality monitoring and reduction of waste. The meter can also be used for monitoring of preliminary, interim and final products during blending operations - and for verification and documentation of process steps. Because it reduces the need for offline laboratory measurements, it also improves plant availability and speeds response to changing conditions.

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