Measuring and testing – Dynamometers – Responsive to force
Patent
1990-08-29
1992-09-08
Ruehl, Charles A.
Measuring and testing
Dynamometers
Responsive to force
73769, G01L 122, G01L 1902
Patent
active
051448475
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a pressure or force measuring device comprising a housing, a measuring body subjected to a measured pressure or measured force, signal generators for generating measuring signals corresponding to the deformation of the body, and an evaluating circuit processing the measuring signal for generating an output signal proportionate to the measuring pressure or measuring force.
When measuring pressures which vary with time, measuring errors occur due to mass accelerations in the mechanical part of such pressure sensors. Pressure shocks, stochastic pressure variations and external disturbances, for example vibrations acting on the housing, lead repeatedly to transient or settling phenomena. During this transient phenomena the measured values indicated have dynamic errors. Fundamentally, due to its construction consisting of the mass of the pressure-influenced part and the return force of the force measuring element acting as spring, the pressure sensor reacts with a dynamic behaviour corresponding to a damped spring-mass system.
DE-PS 694,803 discloses a pressure sensor of the type mentioned at the beginning in which the measuring body subjected to the measured pressure and a reference body are each supported via piezoelectric measuring elements on the housing, the measuring signals of the two force meters being superimposed subtractively on each other. If during a pressure measurement vibration forces act on the housing they are transmitted via the two force measuring elements to the measuring body and reference body and generate equisized and equidirectional signals which cancel each other out so that only the pressure force exerted by the measured pressure on the measuring body is measured. However, fundamentally with this arrangement only the acceleration forces acting on the housing can be excluded from the measurement. Dynamic measuring errors due to sudden changes in the pressure to be measured are not covered. However, even the dynamic components of the forces acting on the housing are completely compensated only if in an ideal case an exactly synchronous movement of measuring body and reference body is assumed on housing vibrations or shocks. Because of unequal masses, material damping, etc., in a real case phase displacements between measuring and reference bodies necessarily occur and falsify the measurement result.
The invention is based on the problem of further developing a pressure or force sensor of the type indicated with the simplest and most economical construction possible in such a manner that a measurement result is obtained which as far as possible is not falsified by the dynamic inherent behaviour of the sensor, in particular on rapidly changing measured pressures or forces.
By the invention, the force components generated by the dynamic spring-mass behaviour of the sensor are detected and compensated in the evaluating circuit so that the measuring signal obtained represents substantially exactly the time profile of the force to be measured. This is done in that by the evaluating means at any instant the dynamic force equilibrium for both masses is calculated at least in simple approximation, and indeed exactly in accordance with the further development.
A further advantage of the invention resides in that the force or pressure sensor can be made substantially without damping. Because of their dynamic behaviour, hitherto usual pressure or force sensors require a damping to minimize as far as possible the influence of the transient or settling phenomena on the measurement result. However, such a damping in the sensor system also suppresses the force peaks of the force profile to be measured and lead in particular with high-frequency pressure or force variations to erroneous measurement. The invention permits a practically damping-free construction of the sensor so that the latter can respond substantially without delay to changes in force or pressure.
Embodiments of the invention will be explained in detail with the aid of the drawings, wherein:
FIG. 1
REFERENCES:
patent: 3201983 (1965-08-01), Hebert et al.
patent: 4064544 (1986-08-01), Konomi et al.
patent: 4155265 (1979-05-01), Pickett et al.
patent: 4422336 (1983-12-01), Beebe
F. L. Crosswy et al, "Dynamic Force Measurement Techniques", Instruments and Control Systems, vol. 43, No. 2, Feb. 1970, pp. 81-83.
Ruehl Charles A.
Zach Johann
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