Arthur J Hubbard

US Patent:

48438812, Jul 4, 1989

Filed:

Dec 24, 1987

Appl. No.:

7/137955

Inventors:

Arthur C. Hubbard - Arlington VA

Assignee:

Aalborg Instruments & Controls - Monsey NY

International Classification:

G01F 168

US Classification:

7320416

Abstract:

A mass flow sensing system in which two heating/sensing coils are disposed about a conduit through which the fluid passes, the coils being located up and down stream along the conduit and close proximity to one another. Each coil forms one leg of a bridge circuit. Each bridge circuit has a regulator amplifier circuit. One input of the amplifier is coupled to one side of the bridge coil which is joined to a first fixed resistor. The other side is coupled to the juncture of the other two of the fixed resistor. The output of the amplifier is fed back to the juncture of the first and second fixed resistor. The fluid is heated to well above its ambient temperature as it enters the conduit. Changes in current necessary to maintain the heater/sensor coils at a constant operating temperature are sensed by a differential amplifier connected to the juncture of the first and second fixed resistors of each bridge.