Measuring and testing – Testing by impact or shock – Specimen impactor detail
Patent
1994-01-07
1995-05-30
Chilcot, Jr., Richard E.
Measuring and testing
Testing by impact or shock
Specimen impactor detail
73 1205, G01N 300
Patent
active
054191769
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method of, and apparatus for, detecting and analysing particles, and is more specifically concerned with the detection and analysis of such particles using a sensor which is responsive to particle impact.
BACKGROUND TO THE INVENTION
It is known to detect particles, such as sand, moving in a flowing fluid, for example oil, with a sensor which generates a signal in response to particle impact. Such a sensor conventionally comprises a piezo-electric element coupled to the sensor housing so that collision of particles with the housing deform the element, causing the latter to generate a voltage signal which may be analysed to obtain information on the nature of the impact.
In conventional analysis techniques, the signal is amplified, unwanted frequency components filtered-out and a thresholding procedure is then applied in order to determine whether the amplitude of the signal is greater than a pre-determined threshold level. If that threshold is passed, the detection of an impact is registered in a counter.
Since the magnitude of the sensor signal is related to the force of particle impact, a series of different threshold levels may be employed in order to give an indication of the relative magnitudes of particle impacts. The energy dissipated on impact is proportional to the momentum of the particle involved, from which an indication of the mass of the particle can be obtained if the velocity of impact is known (or deduced from, for example, the flow-rate of the fluid).
An example of such an arrangement is shown in U.S. Pat. No. 4,240,287.
One disadvantage of such an arrangement is that an accurate measure of particle size is not obtained, since the various impact signals are merely sorted into a number of ranges dictated by the threshold levels.
SUMMARY OF THE INVENTION
According to one aspect of the present invention , there is provided a method of detecting and analysing moving particles using a transducer which generates an electrical signal in response to a particle impact, having an amplitude which is related to the force of particle impact, the method comprising the steps of: given threshold and noting any local maximum values whilst the transducer output signal exceeds the said threshold; maximum amplitude so as to discriminate between electrical noise spikes and an amplitude excursion caused by a particle impact; and detected local overall maximum value and whose timing bears a fixed relationship to the time at which the local overall maximum value occurred to thereby generate a signal which is indicative of the momentum and position in time of a particle impact.
Since this method provides a direct measurement of the true maximum amplitude of an excursion caused by a particle impact, a relatively accurate indication of the momentum of the associated particle may be obtained.
As mentioned the method proposed allows one to discriminate between the actual amplitude excursion produced by an impact and any amplitude excursions in the transducer oscillation which may be caused, for example, by noise.
In order to improve the overall sensitivity of the method the transducer should be only lightly damped. In this case the impact of a particle will produce a series of amplitude excursions of diminished magnitude in the transducer output signal and the time taken for these amplitude excursions to diminish to an insignificant level is called the recovery time of the transducer.
When the flux of particles incident on the transducer is relatively low it is rare for an impact to occur during the recovery time of the transducer. However, larger fluxes may cause a significant number of impacts to occur within one or more recovery times.
If a second particle impact occurs within the recovery time of the transducer the perceived amplitude of the local overall maximum value of the transducer signal for the second impact will not be an accurate measure of the momentum of the second impact due to the presence of the decaying amplitude excursions caused by the first
REFERENCES:
patent: 3418546 (1968-12-01), Beavers et al.
patent: 3557616 (1971-01-01), Landon, Jr. et al.
patent: 3587291 (1971-06-01), Escallier et al.
patent: 3805591 (1974-04-01), Willis et al.
patent: 3844174 (1974-10-01), Chabre
patent: 4184372 (1980-01-01), Brown
patent: 4770527 (1988-09-01), Park
patent: 4807482 (1989-02-01), Park et al.
patent: 5113680 (1992-05-01), Matsura et al.
patent: 5144251 (1992-09-01), Fasching et al.
Chilcot Jr. Richard E.
Dougherty Elizabeth L.
Rig Technology Limited
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