Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1983-04-27
1985-01-22
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Diaphragm
73431, 73756, 128748, 128903, A61B 500, G01L 912
Patent
active
044944110
DESCRIPTION:
BRIEF SUMMARY
The invention concerns itself with a pressure detector according to the preamble of claim 1.
Those pressure detectors are known already, the resonant circuit being driven by an oscillator and the inherent frequency thereof, which is normally in the MHz range, fluctuating depending on the changeable capacity so that the frequency fluctuation of the oscillator signals can be converted into a correspondingly fluctuating direct voltage by means of a frequency detector. The frequency detector for such a pressure detector is conventionally made adjustable so that it can be adjusted to the carrier frequency of the detector-oscillator system, for instance, in a manner such as to give no voltage when the detector is not exposed to any pressure. (VDI Report No. 93, "Process of the Electrical Pressure Measuring and Application Thereof", Dusseldorf, 1966, p. 44).
These pressure detectors known already are not adequate for all cases, since their dimensions are too large, they are connected by cables with the other components of the system, and they have no sufficient long-term stability.
There are also known capacitive pressure probes in which a thin, stretched high-quality steel diaphragm is welded with a high-quality steel housing, and that with an insulated electrode not situated under the diaphragm forms a variable capacity. This known pressure probe has electronics with pulse width modulation of a center frequency of about 100 kHz, a digital control converting the pressure-depending capacity changes in a direct voltage signal (Series 237 of Setra Systems Inc.). But the stability of this pressure probe and in particular the temperature dependence are not sufficient for all uses, for many of which the dimensions are far too large, mainly on account of the expensive electronics situated in the immediate proximity of the variable capacity, to obtain the direct-voltage measuring signal, and the required cable connection with the other components of the whole system is likewise inadmissible in a series of cases.
Also known are piezoresistive semiconductor pressure probes that are offered in small dimensions (about 2 mm. diameter and 6 mm. length) (EPI-080 of Entran Devices, Inc.), but these require expensive gauging steps on account of their insufficient stability and temperature dependence (M. Gaaz, "Registration of Intracranial Pressure", University Appointment Paper, Wurzburg 1980, p. 45-56), which make necessary at least periodically a physical connection with other components of the system.
In addition it has also become known already to insert a semiconductor pressure detector in a wireless transmitting probe together with a temperature detector with which to modulate, with the signals of both detectors, a telemetry transmitter situated in the probe and analytically to eliminate the temperature drift of the pressure detector, wherein the probe was wirelessly supplied with energy ("Medical & Biological Engineering & Computing", January, 1979, pages 81-86). But hereby zero drift and calibration of the pressure meter cannot be determined and much less adjusted; in addition, the stabilities of both the transmitter oscillator and the receiver oscillator enter in the measurement, and each one of these deficiencies alone already forbids a long-term measuring even if in the publicity a long operation period has been discussed as possible. Besides, it is common to all known pressure detectors that the production costs are high.
Accordingly, the invention is based on the problem of making available a pressure detector that is small, that requires a small cost of production, that has great stability and independence of temperature, and that can be used without physical connection to the whole system (cable, pressure hose). Those pressure detectors were in general needed where the measuring or pressure space should or must remain movable independently of the whole measuring system, but also where pressure had to be measured in places of difficult access. By way of example herebelow, the measuring of the intracranial pressure
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Funkschau 1961/Heft 10, Wendel-Topfkreise fur Kreisguten uber 300, Von Ruf Dierke.
Koschke Peter
Novak Pavel
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Woodiel Donald O.
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