Patent ID: 7956601

Claim:
Process for detecting electrically conductive particles flowing in a liquid within a pipe section at a velocity v, comprising the steps of: exposing the liquid to periodic alternating electromagnetic fields by means of a transmitter coil to induce eddy currents in the particles, by means of a probe which is made as a coil arrangement and which is characterized by an effective width, producing a periodic electrical signal based on the eddy currents induced, the signal having a carrier oscillation with at least one of an amplitude and a phase which is modulated by the particles when the particles travel into the effective width of the coil arrangement, filtering the signal by means of a frequency-selective first filter unit, sampling the signal filtered by the first filter unit by means of a triggerable A/D converter stage to obtain a demodulated digital measurement signal, filtering the digital measurement signal by means of a digital, frequency-selective adjustable second filter unit to obtain a useful signal, and evaluating the useful signal to detect passage of electrically conductive particles within the liquid moving in the pipe section, triggering A/D converter stage with a n-th, integral fraction of the frequency of the carrier oscillation, n being a function of a particle frequency which arises as the quotient of the flow velocity of the liquid v and the effective width of the coil arrangement, and setting the frequency-selective second filter unit as a function of the particle frequency, wherein the transmitter coil surrounds the pipe section, the coil arrangement having at least one first inductive receiver coil surrounding the pipe section and a second inductive receiver coil which is spaced axially relative to the first receiver coil and which surrounds the pipe section, the receiver coils being located in a region of the transmitter coil and are subtractively connected, the transmitter coil forming a primary side and the receiver coils forming a secondary side of a transformer arrangement, comprising the further steps of: outputting a difference signal according to the eddy currents induced by the transmitter coil, forming the useful signal from the difference signal, estimating the flow velocity of the detected particles from the difference signal, and using the estimated flow velocity to determine the flow velocity v and using the flow velocity v to determine an operating state of a machine through which said liquid has passed.