AUTOMATIC GAIN CONTROLLING CIRCUIT FOR ULTRASONIC FLOWMETER

摘要

PURPOSE:To make it possible to prevent the change of the point of reception detecting time if the envelope of the received ultrasonic pulse changes by amplifying said pulse according to the difference between the peak value and the preset value of the wave of specified number-th cycle of the received ultrasonic pulse. CONSTITUTION:The wave of specified number-th cycle of the received ultrasonic pulse is detected, and the amplification factor is regulated according to the difference between the peak value and the preset value thereof so that the signal intensity is made constant to detect the arrival time. For example, the ultrasonic pulse inputted to a terminal 5 is amplified in an amplifier 6 and then supplied to a peak detecting circuit 7 and a comparator 8, and the peak value of the specified number-th cycle is held in a circuit 13 by the operation of a frequency divider 11 and the like. Then, this is compared with a reference voltage 14, and according to the difference, the gain of the amplifier 6 is varied so that said peak value is made constant to detect the reception time by using a detector K. Thereby, measurement which is of less error and stable can be performed independently of the change of the envelope of the received pulse or the like.