| 摘要 |
An apparatus for separating and collecting plasma from whole blood includes a volume monitoring system which provides a continuous display of the volume of plasma collected. A transducer circuit within the system develops an electrical signal frequency-dependent on the weight of the collected plasma. The frequency of this signal over a present measurement interval is periodically compared with the frequency of the signal over a preceding measurement interval to develop a difference signal. If the difference is determined to be positive and less than a predetermined maximum collection rate so as to constitute a valid collection increment, the difference is cumulatively added to previous collection increments in a cumulative display counter to provide a collected volume display, and the frequency of the present measurement interval is taken as a frequency of the preceding measurement interval for the next comparison. If the difference is negative, and therefore not a valid collection increment, then no increment is accumulated. If the difference exceeds the predetermined maximum collection rate, and is therefore not a valid collection increment, then no increment is accumulated and the frequency of the preceding measurement interval is not updated. Since the display counter is advanced only for valid collection increments, it provides a display of collected plasma volume, without regard to tare weight changes and physical disturbances to the collection bag. |
