3J-3 Reciprocal Operation of Ultrasonic Transducers: Experimental Results

Abstract

Abstract-Ultrasonic transit-time flow-meters estimate fluid or gas flows from the difference in times of flight of upstream and downstream acoustic pulses. However, any delay differences arising from sources other than the flow to be measured will cause a troublesome "zero flow" offset error.In theory, the transducers used in the measurement system should not influence the zero flow error, as electroacoustic systems based on piezoelectric transducers have been shown to be reciprocal (when the media is stationary). However, care is required when designing the electrical interfaces for the piezoelectric transducers, if reciprocity in the system is to be utilized.This work presents technique and measurements that apply reciprocity to an ultrasonic transit-time flow-meter. Specialized electrical transducer interfaces with options to drive the transducers from either low or high impedance sources were used. Combined with a high-impedance receive mode these options made it possible to change the conditions for reciprocity in the system.We show reduced delay difference in 9 cases out of 10 when trying to utilize the reciprocal property compared to when we disregard it in favor for larger excitation energy. The delay improvements were accompanied by reduced differences between the center frequencies of the signals from the two paths.

Concepts and architecture for a thumb-sized smart IoT ultrasound measurement system

“…Additional losses comes from parasitic capacitances and inductances [14]. The minimization of these losses can only be achieved by shortening lead lengths and minimizing interconnect dimensions in combination with a circuit design that utilizes the energy storage provided by the piezoelectric transducer [15]. It is obvious that an ASIC implementation of such a circuit design is desirable.…”

An Algorithm to Minimize the Zero-Flow Error in Transit-Time Ultrasonic Flowmeters

“…Minimizing the offset error is commonly done by matching the impedance of the receive circuit to the impedance of the transmit circuit, in order to maximize the reciprocity of the measurement system [3], [5], [6]. This method is good at reducing the offset error, but a residual offset usually remains.…”

Research and realisation of reciprocal electronic circuits for gas ultrasonic flow meter

“…where L is the length of the acoustic path; C f is the speed of sound in the medium; v m is the mean flow velocity on the acoustic path; and ϕ is the path angle. Using (1) and (2) v m can be derived as shown in (3)…”

“…In 2002, Deventer and Delsing [2] showed that variations between the two transducers cause false estimates of flow and indicated which parameters have the largest influence. In 2006, Borg et al [3] preserved high impedance across the transducer terminals in both transmit and receive phases to achieve reciprocal operation and obtained clear improvements in both transit-time stability and frequency stability. In 2007, Lunde et al extended the reciprocal operation theory of USMs by taking into account the finite electrical impedances of the electronics and transducers, derived design criteria for reciprocal operation of USMs [4].…”