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A METHOD FOR MEASUREMENT OF MINUTE VOLUMES OF LIQUID

IP.com Disclosure Number: IPCOM000006708D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-24
Document File: 3 page(s) / 142K

Publishing Venue

Motorola

Related People

Barry Boaz Groman: AUTHOR

Abstract

The described method allows to measure, simply and inexpensively, minute amounts of liquids which can not be measured by conventional laboratory instruments. The method reduces the three dimensional volume meas- urement problem into a two dimensional measurement, so a common vision system can be utilized. The method described is independent of the material composition of the liquid which is to be measured.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

A METHOD FOR MEASUREMENT OF MINUTE VOLUMES OF LIQUID

by Barry Boaz Groman

ABSTRACT

  The described method allows to measure, simply and inexpensively, minute amounts of liquids which can not be measured by conventional laboratory instruments. The method reduces the three dimensional volume meas- urement problem into a two dimensional measurement, so a common vision system can be utilized. The method described is independent of the material composition of the liquid which is to be measured.

BACKGROUND INFORMATlON

  Current volume measurement methods utilize scan- ning techniques which are slow and require expensive scanning devices. These devices utiliie non-contact sur- face scanning to obtain the surface shape of the liquid and then integrate over the surface to calculate the mate- rial's volume.

  When a minute volume of liquid is required to be measured, non-contact scanning devices may yield large error since such methods depend on the material com- position of the liquid. Materials which do not reflect the scanning energy exactly off the surface will give large errors with respect to the entire volume of the liquid.

METHOD DESCRIPTION

  This volume measurement method uses two flat plates-such as microscope slides. The liquid to be meas- ured is placed on one of the plates and then the other plate is lowered onto the plate with the liquid. As the second plate is lowered onto the first, the material spreads between the two plates. Spacers of known thickness are used to stop the plates from touching, see Figure 1.

  A calibrated vision system with the camera mounted normal to the plates is then utilized to measure the area of the deformed liquid. The measured material area mul- tiplied by the thickness of the spacers yields the volume of material.

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MEASUREMENTISSUESANDERRORS

  An inherent measurement error is present due to the physical shape the liquid assumes when placed between two plates. As Figure 2 suggests, both meas- urement of a high surface tension and low surface ten- sion liquid will yield a greater volume then actual, since a vision system is utilized for the area measurement. The vision system calculates the area of the material by the outliie of the material, which will always yield an error when the material is assumed to have a uniform thickness. The camera resolution should be suff%ently high so the area of the material can be precisely measured.

  As the thickness of the spacer...