Hot wire anemometer and pulmonary gas flow monitor combination capable of fast accurate calibration

摘要

A hot wire sensor has a cylindrical light-transparent tube having two opaque patches adjacent the two tube ends, respectively, and with one platinum "hot" wire mounted about centrally therein and another platinum wire mounted adjacent thereto. A gas flow monitor includes a resistive bridge circuit, connected to the hot wire sensor. In the bridge circuit, the two platinum wires become two of the adjacent bridge branches. A DC voltage supply of the monitor is connected across the bridge at the bridge junction of the platinum wires, heating the one but not the other owing to disparate resistances in the bridge branches. A calibration socket is mounted vertically on an outer wall of the monitor housing. To calibrate the sensor, a tube end is inserted into the socket holding the tube axis horizontal and the tube is rotated until the opaque patch breaks a light beam between a LED and a photo transistor at the periphery of the socket. At that position the one "hot" wire is horizontal and the breaking of the light beam electrically enables (unlocks) the bridge so that an adjustment of one of the bridge arm resistances can be made to obtain a bridge output voltage of predetermined value corresponding to zero flow of gas through the sensor tube.