Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1986-05-27
1987-12-22
Ruehl, Charles A.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
G01F 166
Patent
active
047139714
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for determining the (mean) velocity in a flowing fluid, of the type including an ultrasound transmitter and a receiver coupled therewith for receiving ultrasounds reflected from the fluid, which are amplified and demodulated so as to produce a low-frequency Doppler-signal, that is subsequently analyzed by a spectrum analyzer, consisting of a number (n) of bandpass filters, peak detectors being provided to determine the energy values of the frequency components obtained by said bandpass filters, and a calculation unit being used to calculate that frequency, at which the low-frequency Doppler-signal appears to have a maximum, the latter being a measure for the mean velocity of flow.
A device of this type is known from the DE-PS No. 1,791,191 in which the application for determining the flow rate of blood in blood vessels is described. The velocity values obtained by this well-known device device appear to deviate rather substantially from the values obtained by means of an other well-known type of meter, the electromagnetic flowmeter, which is generally considered as an accurate one.
The measuring device, operating according to the Doppler principle, however, has the practical advantage over other types of flowmeters, that it may also be used in circumstances in which other types of measuring devices would not be useful or less appropriate. For as a metter of fact this meter can be easily put in place, is not subject to wastage and is relatively inexpensive.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to improve the device of the type above referred to and more particularly to improve its measuring accuracy.
Tests run in flowing fluids of different composition, density and volume rate, have led to the inference that interference in the Doppler-spectrum caused by background noise, is taking place in a rather fixed distribution over the individual frequency bands. It has been found that the successively measured frequency components may be approximately corrected to the actual Doppler-spectrum with the aid of a simple correction curve, which is substantially determined by the intensities, measured by the bandpass filters at the lower and upper limits of the spectrum respectively.
On the basis of this insight, the device according to the invention is characterized in that the calculation unit includes components which are designed to cause the measured energy values of the individual frequency components of the frequency spectrum to decrease according to a monotonically decreasing correction curve.
According to a further feature of the invention, the calculation unit is adapted to operate according to a correction curve, which connects a location representing a value between 65% and 85% of the energy value measured by the lowest bandpass filter with a location representing a value between 35% and 45% of the energy value measured by the highest bandpass filter.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further explained, by way of example, with reference to the accompanying drawings wherein:
FIG. 1 is a block diagram showing the device according to the invention,
FIG. 2 shows a Doppler-energy spectrum of a medium and
FIG. 3 shows the calculation unit of the spectrum analyzer block of FIG. 1.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
The device for determining the flow rate of a fluid flowing through a pipe, as diagrammatically shown in FIG. 1, comprises a transmitter 3 placed on the pipe wall 2, which transmits a beam of sound waves 4. The beam of sound waves 5 reflected from the flowing fluid is received by a receiver 6 also placed on the pipe wall 2. The Doppler-effect causes a frequency shift between the transmitted and received beams of sound waves. This frequency shift is expressed in the energy spectrum of the output signal of receiver 6. Upon amplification in block 7 and demodulation in block 8 the low-frequency Doppler-signal is obtained from this signal. An example of the energy spectrum of a low-frequency Doppler-signal is ind
REFERENCES:
patent: 3675192 (1972-07-01), Fahrbach
patent: 4117538 (1978-09-01), Shrader et al.
patent: 4413531 (1983-11-01), Karplus et al.
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