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Non-invasive low frequency elastic wave fluid level sensing system for sludge laden environments

  • US 6,192,751 B1
  • Filed: 11/18/1997
  • Issued: 02/27/2001
  • Est. Priority Date: 11/18/1997
  • Status: Expired due to Fees
First Claim
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1. A non-invasive elastic wave fluid level sensing system for use in sludge laden environments, comprising:

  • a transmitting transducer mounted on an outer face of a wall of a container for a fluid wherein the fluid is of a nature to deposit a layer of sludge on an inner face of the wall of the container and wherein the effect of the layer of sludge on the inner face of the wall of the container on the propagation of an elastic wave through the wall of the container is similar to the effect of a presence of the fluid on the inner face of the wall of the container, a receiving transducer mounted on the outer face of the wall of the container along a propagation path for an elastic wave extending through the wall of the container and between the transmitting transducer and the receiving transducer, a signal generator connected to the transmitting transducer for driving the transmitting transducer to transmit an elastic wave through the wall and along the propagation path to the receiving transducer, the elastic wave having a frequency of less than one kHz, and a signal processor connected from the signal generator and the receiving transducer for determining a characteristic of the elastic wave along the propagation path and determining a change in the elastic wave characteristic between when a fluid is present in the container in the region of the propagation path and when a fluid is not present in the container in the region of the propagation path, and wherein the signal processor further comprises a cross-correlation detector for determining a cross-correlation detector for determining the change in the elastic wave characteristic as a function of both the degree of phase shift and the amount of amplitude difference between a stored baseline signal representing the received elastic wave with the tank fluid level at one state and a second (and a second)signal representing the received elastic wave with the tank fluid level at a changed state.

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