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Compact Instruments Measure Helium-Leak RatesCompact, lightweight instruments have been developed for measuring small flows of helium and/or detecting helium leaks in solenoid valves when the valves are nominally closed. These instruments do not impede the flows when the valves are nominally open. They can be integrated into newly fabricated valves or retrofitted to previously fabricated valves. Each instrument includes an upstream and a downstream thermistor separated by a heater, plus associated analog and digital heater-control, signal- conditioning, and data-processing circuits. The thermistors and heater are off-the-shelf surface mount components mounted on a circuit board in the flow path. The operation of the instrument is based on a well-established thermal mass-flow-measurement technique: Convection by the flow that one seeks to measure gives rise to transfer of heat from the heater to the downstream thermistor. The temperature difference measured by the thermistors is directly related to the rate of flow. The calibration curve from temperature gradient to helium flow is closely approximated via fifth-order polynomial. A microprocessor that is part of the electronic circuitry implements the calibration curve to compute the flow rate from the thermistor readings.
Document ID
20110023601
Acquisition Source
Kennedy Space Center
Document Type
Other - NASA Tech Brief
Authors
Stout, Stephen
(DYNACS Engineering Co., Inc. Cocoa Beach, FL, United States)
Immer, Christopher
(DYNACS Engineering Co., Inc. Cocoa Beach, FL, United States)
Date Acquired
August 25, 2013
Publication Date
February 1, 2003
Publication Information
Publication: NASA Tech Briefs, February 2003
Subject Category
Man/System Technology And Life Support
Report/Patent Number
KSC-12216
Distribution Limits
Public
Copyright
Public Use Permitted.
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