Method of determining liquid flow in a conduit

A method for measuring the velocity of a liquid flowing continuously or discontinuously in a conduit at rates between about 20 and 1000 cm.sup.3 /minute comprising:

• (A) injecting a thermopulse of between about 5 and 100 ms in duration into the liquid by means of a wire having a weight of less than about 15 mg and being heated by the discharge of a condenser centrally mounted in the conduit carrying said liquid,
• (B) simultaneously adjusting a bistable multivibrator to its set mode so that it allows pulses from a pulse generator to pass through a gate to a pulse counter,
• (C) activating said pulse generator for at least one measurement cycle,
• (D) detecting the arrival of the ascending flank of said pulse with a differential thermocouple mounted in said conduit between about 5 and 500 mm downstream of said heater,
• (E) amplifying the detection signal of said sensor and passing it to a comparator,
• (F) using said amplified signal to activate said comparator and using the output of said comparator to activate the reset mode of said bistable multivibrator thereby closing said gate to further pulses of said pulse generator,
• (G) reducing the value accumulated in said pulse counter by the heat up time of said wire,
• (H) converting the value accumulated in said pulse counter during the set/reset cycle of the multivibrator to a value equivalent to the velocity of said liquid by means of a permanently programmed ROM-code converter, and
• (I) storing the value accumulated in said impulse counter until the next set/reset cycle of the multivibrator is completed.