Improved precision of hydraulic conductance measurements using a Cochard rotor in two different centrifuges
Résumé
An improved way of calculating hydraulic conductance (K) in a Cochard Cavitron is described. Usually K is determined by measuring how fast water levels equilibrate between two reservoirs while a stem spins in a centrifuge. A regression of log meniscus position versus time was used to calculate K and this regression method was compared to the old technique that takes the average of discrete values. Results of a hybrid Populus 84K shows that the relative error of the new approach is significantly lower than the old technique by 4~5 times. The new computational method results in a relative error less than 0.5% or 0.3% from 8 or 12 points of measurement, respectively. The improved precision of K measurement also requires accurate assessment of stem temperature because temperature changes K by 2.4% oC-1. A computational algorithm for estimating stem temperature stability in a Cavitron rotor was derived. This algorithm provides information on how long it takes stem temperature to be known to within an error of ±0.1 oC.