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1. (WO2017147721) METHOD AND SYSTEM FOR CONTROLLING VOLTAGE APPLIED ACROSS A PIEZOELECTRIC STACK OF A DOWNHOLE ACOUSTIC TRANSMITTER

Pub. No.:    WO/2017/147721    International Application No.:    PCT/CA2017/050298
Publication Date: Sat Sep 09 01:59:59 CEST 2017 International Filing Date: Sat Mar 04 00:59:59 CET 2017
IPC: E21B 47/16
Applicants: XACT DOWNHOLE TELEMETRY INC.
Inventors: MCRORY, John Godfrey
Title: METHOD AND SYSTEM FOR CONTROLLING VOLTAGE APPLIED ACROSS A PIEZOELECTRIC STACK OF A DOWNHOLE ACOUSTIC TRANSMITTER
Abstract:
Methods, systems, and techniques for controlling voltage applied across a piezoelectric stack of a downhole acoustic transmitter. At least one of the temperature of the stack and the compressive stress applied to the stack is monitored. At least one of the temperature of the stack and the compressive stress applied to the stack is compared to a temperature threshold and a stress threshold, respectively. When the stack signal is an alternating voltage signal and when at least one of the temperature of the stack and the compressive stress applied to the stack respectively exceeds the temperature threshold and the stress threshold, the stack signal is modified such that a negative polarity portion of the stack signal has a maximum magnitude less than a magnitude of a negative polarity limit.