Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1990-02-28
1991-10-01
Ruehl, Charles A.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
G01F 166
Patent
active
050522302
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for flow rate measurement by means of ultrasonic waves which are propagated in a medium flowing through a measuring tube between two ultrasonic transducers which are arranged spaced apart from each other and of which the one operates as transmitting transducer converting an electrical transmission signal to an ultrasonic wave of the same frequency whilst the other operates as receiving transducer converting the incoming ultrasonic wave to an electrical reception signal of the same frequency, the phase shift between the transmission signal and reception signal being measured to determine the flow rate.
In this flow rate measuring method the flow rate to be measured is derived from the phase shift between the transmission signal and the reception signal in an ultrasonic wave propagated in one direction if the velocity of sound is known. By determining the phase shifts in an ultrasonic wave propagated in the flow direction and an ultrasonic wave propagated against the flow direction it is possible from the difference between said phase shifts to obtain a measurement result for the flow rate independent of the velocity of sound.
In a method of this type known from Swiss Patent 628,140 the phase shift between the transmission signal and the reception signal determined for each propagation direction is converted to a DC voltage which is stored in a sample and hold circuit. The two stored DC voltages are then applied to the two inputs of a differential amplifier which thus furnishes at the output a differential voltage which is proportional to the difference between the phase shifts and thus to the flow rate. In addition, by forming the sum of the stored DC voltages a voltage is obtained which is proportional to the velocity of sound in the medium. Finally, in this known method the frequency of the ultrasonic wave is regulated in dependence upon the phase shifts determined to an optimum value and the flow rate obtained from the differential voltage is corrected in dependence upon the frequency set.
This known method requires high expenditure on precise analog circuits but nevertheless is still liable to the inevitable causes of errors in any analog signal processing so that the measurement accuracy obtainable is limited. Furthermore, the output signal obtained is available in the form of an analog voltage which is not suitable directly for digital evaluation, for example by a microcomputer.
The problem underlying the invention is the provision of a flow measurement method of the type mentioned at the beginning which with relatively small circuit expenditure permits flow rate measurement with great measuring accuracy in digital manner and therefore furnishes the measurement result in the form of a digital signal.
According to the invention this is achieved in that in measuring time intervals each having a duration corresponding to the phase shift the periods of a signal having a counting frequency are counted which counting frequency is substantially higher than the measuring frequency corresponding to the frequency of the transmission signal, that the start phase which the counting frequency signal has at the beginning of each counting operation with respect to the measuring time interval is varied from measuring time interval to measuring time interval in a measuring cycle including a plurality of consecutive measuring time intervals and that the counts obtained in the course of the measuring cycle are evaluated to form a measured value with increased measurement resolution.
In the method according to the invention by counting the periods of a counting frequency during the measuring time intervals corresponding to the phase shifts the phase measurement is reduced to a digital time measurement which can conveniently and reliably be carried out with the widely used integrated digital circuits. However, there is the problem that the digital measurement has a system-inherent quantizing error which limits the resolution obtainable in the measurement because the smallest distinguishab
REFERENCES:
patent: 4011755 (1977-03-01), Pedersen et al.
patent: 4164865 (1979-08-01), Hall et al.
patent: 4445389 (1984-05-01), Potzick et al.
patent: 4527433 (1985-07-01), Gutterman
Lang Michael
Steinacher Michael
Flowtec AG
Ruehl Charles A.
LandOfFree
Method and arrangement for flow rate measurement by means of ult does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and arrangement for flow rate measurement by means of ult, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and arrangement for flow rate measurement by means of ult will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1746408