Apparatus for measuring fluid flow

Abstract

Abstract FLUID-FLOW REPOSNSIVE APPARATUS COMPRISES TWO THERMOCOUPLE JUCTIONS, BOTH MOUNTED IN THE FLUID, CONNECTED TO AN AMPLIFIER IMPUT. AN ENERGIZING CIRCUIT, INCLUDING A SERIES-CONNECTED SWITCHING TRANSISTOR, IS CONTROLLED BY A VARIABLE MARK/SPACE RATIO PULSE GENERATOR. DURING ONPERIODS OF THE PULSE GENERATOR THE ENERGIZING CIRCUIT FEEDS HEATING CURRENT THROUGH BOTH JUNCTIONS. ONE JUNCTION IS HEATED TO A HIGHER TEMPRATURE BECAUSE THE OTHER HAS RELATIVELY HIGH RESISTANCE CONNECTED TO IT. A DIODE ACROSS THE AMPLIFIER PROVIDES SUBSTANTIALLY COMPLETE NEGATIVE FEEDBACK ACROSS IT DURING THE THE ON-PERIODS. DURING THE OFF-PERIODS, THE TRANSISTOR IS OFF AND THE THERMOCOUPLE E.M.F. DRIVES THE AMPLIFIER, THE DIODE ACROSS THE AMPLIFIER NOW BEING CUT OFF. THE THERMOCOUPLE E.M.F. IS THUS DEPENDENT ON THE RATE OF LOSS OF HEAT FROM THE HOTTER OF THE TWO THERMOCOUPLE JUNCTIONS, AND THUS ON THE FLUID FLOW. THE MARK/SPACE RATIO OF THE PLUSE GENERATOR IS AD- JUSTED UNTIL THE MEAN AMPLIFIER OUTPUT HAS A PREDETERMINED VALUE, AT WHICH TIME THE MARK/SPACE RATIO REPRESENTS THE RATE OF FLUID FLOW. IN ANOTHER EMBODIMENT, THE MARK/SPACE RATIO IS AUTOMATICALLY VARIED SUCH THAT THE AMPLIFIER OUTPUT CONTINUOUSLY CYCLES BETWEEN TWO FIXED LIMITS, AND A COMPARATOR MEASURES THE DIFFERENCE BETWEEN THE TWO VALUES OF THE MARK/SPACE RATIO NECESSARY TO ACHIEVE THESE TWO LIMITS, THE COMPARATOR OUTPUT BEING A MEASURE OF THE FLUID FLOW RATE.

Inventors

• 👤 Jack B Collins
• 👤 Richard M D Saw

Bibliographic Details