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US 4,535,637 AGranted
Flow detection apparatus
AssigneeWilgood Corporation
InventorMurray F. Feller
Life of this patent
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AssigneeWilgood Corporation
InventorMurray F. Feller
Estimating the term…
The disclosed flow-detecting apparatus involves gating of phase-related excitation and sensed signals from electrodes close to a flow-activated tracker in a liquid passage. A high gain comparator provides peak-limited signals to the phase-comparison gate. In one form, a pair of excitation electrodes are symmetrical in relation to a single sensing electrode. That electrode supplies a sensed signal to one comparator input, the other comparator input having fixed bias. In another form, a pair of sensing electrodes are disposed in an excitation pattern between a localized excitation electrode and a metal pipe that forms the passage and acts as a second excitation electrode. The sensed signals reach respective input terminals of a high-gain comparator and it responds to the difference between the inputs. Other configurations of the electrodes and their excitation are disclosed, including one that promotes rejection of common-mode spurious signals. A comparator that receives flow-representing signals is stabilized against electrical unbalance by a negative feedback loop having a long time constant. In flow-detection apparatus having a multiple-rotor flow-sensing probe, separate flow-detection circuits are used for the respective rotors. The outputs of the flow-representing circuits are combined. Use of different excitation frequencies for those flow-detection circuits adds assurance of non-interfering operation of the flow-detection circuits.
Flow-detecting apparatus including means forming a liquid flow passage, an alternating excitation source, means for developing an excitation pattern in liquid in a region in said passage and for sensing said excitation pattern, said pattern developing and sensing means including (a) excitation electrode means connected to said excitation source and (b) sensing electrode means, a flow-driven tracker having at least one pattern-distorting element movably cyclically through said region, signal-receiving means connected to said sensing electrode means for providing an output signal that is alternately in phase with or out of phase with the output of the excitation source during cyclic movement of the tracker, and flow-representing signal means including gating means for combining the output of said alternating excitation source with the output of said signal-receiving means to provide trains of signals and signal-interruption intervals representing cyclic movement of said pattern-distorting element past the sensing electrode means and the excitation electrode means.
In a fluid-flow detector, amplitude-to-phase conversion apparatus including a signal comparison device having negative and positive inputs such that an input signal applied only to the positive input develops a like output and the same input signal applied only to the negative input develops inverse output from the signal comparison device, and means for concurrently applying periodic input signals having in-phase peaks of like polarity to said inputs of the comparison device wherein the amplitude of peaks of a particular polarity of the applied signals is higher at one of said inputs at times and higher at the other of said inputs at times, said signal applying means including means responsive to fluid flow, whereby the output of the signal comparison device becomes alternately high and low in dependence on which of the inputs has the higher applied signal of the particular polarity.
Dependencies are inferred from the claim text.
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From the US filing history. Foreign family members aren’t listed.
Using rotating vanes with axial admission: with magnetic or electromagnetic coupling to the indicating device
By using mechanical effects: using rotating vanes with axial admission
By using electric or magnetic effects: by measuring electrical currents passing through the fluid flow; measuring electrical potential generated…
Measuring volume, volume flow, mass flow or liquid level
Term ended 20 Aug 2002 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
In my '354 patent, electrodes are exposed to liquid flowing in a passage, for example water. Alternating-current electrode excitation sets up a pattern of current flow through the liquid. This pattern is variously modified by a liquid-driven vaned rotor of high resistivity material. The liquid is sensed, producing a modulated signal that is demodulated by means of amplitude or phase detectors. The frequency of the demodulated signal represents the flow rate. The operation depends on changing impedances of current paths through the liquid. Flow sensors of that type may be referred to as "impedance flow sensors".
In practice, the electrodes in the flow sensors of the '354 patent are made small, e.g. the ends of rods, so that the modulated signal tends to be relatively weak and requires considerable amplification. Spurious input or electrical "noise" develops at the sensing-electrode input to the detector circuit, tending to interfere with recognition of weak flow-representing signals.
An object of the present invention resides in providing a novel flow sensor of the impedance type.
FIG. 1 is an elevation, partly in cross-section, of a flow-sensing probe useful in novel flow detectors;
FIG. 2 is a side elevation of the probe shown in FIG. 1 as seen from the left;
FIG. 3 illustrates the probe of FIG. 1 installed in a pipe, portions being shown in cross-section;
In FIGS. 1-5, probe 10 has two rotors 12 and 14 and includes a mounting structure consisting of supporting tube 16, a top support 18 and a bottom support 20, and tubes 22 and 24 that act with supports 18 and 20 as a frame for supporting the rotors.
Top support 18 comprises an inverted cup 26 formed of molded plastic providing partial sockets for tubes 22 and 24. Metal tube 16 extends into inverted cup 26 through the end wall of the cup. Electrode 28 (a sensing electrode in FIG. 7) has its lower end exposed and is close to rotor 12. A mass of rigid potting material 29, such as epoxy resin fills the cup. The potting material provides electrical insulation, it unifies tube 16, tubes 22 and 24 and electrode 28, and it is largely immune to deterioration when exposed to the fluid in the pipe which is considered to be tap water in this discussion.
Lower support 20 is conveniently formed of two channels of plastic 30 (FIG. 2) with their edges in abutment, forming a cavity. Tubes 22 and 24 extend through the upper channel and are locked in a mass of rigid potting material 31 such as epoxy resin that fills the channels. Electrode 32 is also locked in the potting material and has its upper end exposed and close to rotor 14.