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            <center>The Rapid Sediment Analyzer</center>
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<font face="Arial" size="2" color="black">The rapid sediment analyzer, or RSA, is a settling tube suitable for the 
analysis of sand-sized material. <br>
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This model is equipped with a differential pressure transducer and calculates 
a size distribution based on the change in pressure with elapsed time. <br>
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&nbsp;<br>
Other RSA’s are equipped with balances that can measure changes in 
weight with time. <br>
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A micro splitter is used to obtain a representative 7 to 8-gram subsample. <br>
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The sample is placed in a tablespoon and dampened with water by pipette to 
prevent trapped intergranular air from impeding the settling process.  The 
sample should then be  manually spread into a thinner layer to facilitate rapid 
disaggregation upon impact with the water surface.<br>
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Care must be taken to introduce the entire sample simultaneously into the 
middle of the settling tube.  If the entire sample is not entered simultaneously, 
the sample will take longer to settle out of suspension and the calculated 
distribution will be finer than actually present. <br>
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If the sample is not entered directly into the center of the tube, 
density currents may form along the tube wall allowing the sample to settle 
more rapidly and this results in a calculated distribution that is coarser than 
actually present. <br>
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The sand grains settle according to Stoke’s Law; pressure decreases as the 
grains settle past the lower transducer port.  The analog signal from the 
transducer is amplified and logged on a computer equipped with an analog-
to-digital converter.  A typical analysis time is approximately 2 minutes. <br>
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