Device and method for measurement of ultrasonic transit times

Abstract

A device for measurement of ultrasonic wave transit times of an ultrasonic flow sensor consists of: 1) a synchronization signal generator, 2) a reference pulse generator, 3) a sine wave generator, 4) an analog signal amplifier, 5) a comparator, 6) a plurality of latch circuits, 7) a digital adder, 8) an integrator, 9) an A/D converter, 10) a master counter, 11) a plurality of edge counters, and 12) an arithmetic circuit. The device measures the ultrasonic wave transit times using a method of averaging the ultrasonic wave arriving times at different measuring points (triggering point). This method has less dependency on triggering threshold level and the ultrasonic signal amplitude, and thus has less dependency on threshold drift, threshold stability, system gain fluctuation, electronic noise and signal amplitude variations. As a result, the method can greatly improve the velocity measurement accuracy and system robustness of an ultrasonic flow sensor.

What is claimed is: 
     
         1 . A device for measurement of ultrasonic wave transit times of an ultrasonic flow sensor consists of:
 a synchronization signal generator,   a reference pulse generator,   a sine wave generator,   an analog signal amplifier,   a comparator,   a plurality of latch circuits,   a digital adder,   an integrator,   an A/D converter,   a master counter,   a plurality of edge counters, and   an arithmetic circuit.   
     
     
         2 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the synchronization signal generator performs the following functions: 1) initiating the measurement cycle, 2) triggering the sine wave generator to start sending sine wave signal to the transmitter of the ultrasonic flow sensor, 3) triggering the reference pulse generator to start generating high frequency clock signal, and 4) commanding the master counter to start counting the reference clock. 
     
     
         3 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the reference pulse generator sends high frequency clock signal to: 1) the master counter, 2) the edge counters, and 3) the latch circuits. These clocks are used to measure the arriving time of the ultrasonic wave at different measuring points. 
     
     
         4 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the sine wave generator sends sine waves to the transmitter of the ultrasonic flow sensor. After certain period of time delay, the sine wave signal arrives at the receiver of the ultrasonic flow sensor with modulated amplitudes. 
     
     
         5 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the analog signal amplifier is AC-coupled. It amplifies the output signal from the receiver of the ultrasonic flow sensor. 
     
     
         6 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the comparator compares the signal received from the analog signal amplifier with the predefined threshold value. When the received signal becomes higher than the threshold value, it outputs a positive pulse. On the other hand, when the received signal becomes lower than the threshold value, it outputs a negative pulse. 
     
     
         7 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the latch circuits are employed to measure the time intervals which are less than one reference clock cycle and cannot be counted by the master counter and the edge counters. 
     
     
         8 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the digital adder is used to add the outputs of all the latch circuits together and then output the summed signal to the integrator. 
     
     
         9 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the integrator converts the short pulse from the adder to an analog exponential signal. 
     
     
         10 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the A/D converter converts the analog output of the integrator to a digital value. 
     
     
         11 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the master counter is used to measure the arriving time of ultrasonic wave at the first measuring point. 
     
     
         12 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the edge counters are used to measure the arriving time of ultrasonic wave at the subsequent measuring points after the first measuring point. 
     
     
         13 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein the arithmetic circuit calculates the ultrasonic wave transit times from the inputs of the master counter, the edge counters and the A/D converter, by averaging the arriving times at different measuring points. This time measurement method has less dependency on triggering threshold level and ultrasonic signal amplitudes, and thus has less dependency on threshold drift, threshold stability, system gain fluctuation and signal amplitude variations. With multi-point triggering and multiple transit-time averaging as explained in previous section, this time measurement method is also more robust again noise interference than prior art. As a result, the method can greatly improve the velocity measurement accuracy of an ultrasonic flow sensor. 
     
     
         14 . The device for measurement of ultrasonic wave transit times of  claim 1 , wherein an even number of latch circuits are employed. And the number of edge counters is always one less than the total number of the latch circuits. For example, if the total number of latch circuits is eight, the total number of the edge counters is seven. 
     
     
         15 . The device for measurement of ultrasonic wave transit times of  claim 14 , wherein two latch circuits and one edge counter are employed. The ultrasonic wave transit time is calculated based on the average of the arriving times at the first and second measuring points. 
     
     
         16 . The device for measurement of ultrasonic wave transit times of  claim 14 , wherein four latch circuits and three edge counters are employed. The ultrasonic wave transit time is calculated based on the average of arriving times at the 1-4 measuring points. 
     
     
         17 . The device for measurement of ultrasonic wave transit times of  claim 16 , wherein the ultrasonic wave transit time is calculated based on the average of arriving times at the third and fourth measuring points. 
     
     
         18 . The device for measurement of ultrasonic wave transit times of  claim 14 , wherein eight latch circuits and seven edge counters are employed. The ultrasonic wave transit time is calculated based on the average of arriving times at the 1-8 measuring points. 
     
     
         19 . The device for measurement of ultrasonic wave transit times of  claim 18 , the ultrasonic wave transit time is calculated based on the average of arriving times at the fifth and sixth measuring points. 
     
     
         20 . The device for measurement of ultrasonic wave transit times of  claim 18 , the ultrasonic wave transit time is calculated based on the average of arriving times at the seventh and eighth measuring points.