Electromagnetic borehole flowmeter system

Claim 1

An improved method for monitoring events occurring at a situs remotely located from an observation situs, wherein juxtaposed such observation situs is signal generating and receiving means for at least both generating an excitation signal and receiving a metering signal, and wherein juxtaposed such remotely located situs is located transducer means for activation by such events, and connector means for effecting communication between such situses, said improved method comprising the steps of: (a) positioning said transducer means at the event situs and effecting, with said connector means, communication between said transducer means and said signal generating and receiving means; (b) coupling said signal generating and receiving means to a first power supply means for providing thereto positive and negative voltage amplitudes; (c) coupling said signal generating and receiving means to a second power supply means for generating an AC square wave excitation signal and transmitting same to said transducer means, said excitation signal synchronized with at least one timing signal provided by said signal generating and receiving means and said first and said second power supply means electrically insulated one from the other; (d) receiving from said transducer means a metering signal indicative of event occurrences at said remotely located situs; (e) dividing down output of said signal generating and receiving means to provide timing signals synchronized with said excitation signal and with said metering signal, said signal generating and receiving means having a master clock period of a frequency ranging from 4 to 15 times that of said square wave excitation signal; (f) selecting, in whole multiples of said master clock period, a sample of said metering signal, said sample selection continuing for at least one such clock period and for less than one-half of the number of such clock periods which comprise the frequency of said excitation signal, and thereafter alternately switching the polarity of said AC square wave excitation signal, whereby transients effected in said metering signal by each such switching are generated after sampling of signal from each positive and each negative amplitude of said metering signal is complete; and (g) deselecting that portion of the metering signal containing switching transients generated by said AC square wave excitation in step (f) supra, said deselecting initiated at the end of each sampling period and continued for a time sufficient to bridge the transition in polarity change of said AC square wave excitation signal whereby the resulting clamped switching transients are prevented from effecting feedback of noise to said sample of said metering signal.