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Abstract

A dynamic controller for quantitative rapid-pulse flow control over a wide dynamic range (1000-to-1) forms a fluid path from a pressurized source to a sink. The fluid path travels, typically in a disposable cassette, from the pressure source via a fast (one millisecond) on-off source control valve into a volume-displacement interface area, thence to a fast on-off load control valve and on to the sink. The load control valve may be replaced by a passive flow restrictor where less dynamic range is required. From the reusable controller side, fast actuators are energized to open the normally-closed valves. A volume sensor mates with the volume-displacement interface area. This sensor uses an incompressible transfer fluid, typically different than and isolated from the deliverable fluid by membranes, to transmit volume displacement change into a transducer area for conversion from volume to a measurable electrical signal, typically a frequency. A known pressure/volume curve for the volume sensor allows pressure monitoring during operation, yielding knowledge of fluid source and load conditions. A flow control method relies on a combination of very short, variable valve-open pulses and design with comparatively large-diameter fluid passageways into the fluid capacitance of the volume sensor, to achieve flow limited more by inertia than viscosity. Distinct high-flow and low-flow control regimes are used. For high flow, bolus volume is maximized by pulsing for one-half the fluid oscillation period determined by the volume sensor fluid capacitance and the flow inertia of the fluid passageway, shutting off at flow reversal. For low flow, pulses typically below 10% of the high-flow pulse width yield small bolus volumes varying as the square of pulse width, providing control over a wide dynamic range of bolus sizes down to fractions of a microliter, permitting moderately high pulse frequencies even at very low average rates, achieving nearly continuous flow. Design with normally-closed, energize-to-open valves assures flow stop if power is lost. In this context, the large fluid passageways lead to a prescribed volume transfer at low valve-open duty cycle, conserving energy and making battery operation practical.

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First Claim