In an oil well instrumentation system, the downhole sensor system is controlled by a computer which is powered-on only during sampling movement. An independent circuit, continuously powered, detects significant sensor rate-of-change values whereby the computer-sampling equipment is powered-on. A self-contained...http://www.google.com/patents/US4866607?utm_source=gb-gplus-sharePatent US4866607 - Self-contained downhole gauge system
