| 摘要 |
<p>Movement of an object (60) such as a plug, ball or dart, in a well is detected by providing an electrical circuit (66) on the object to transmit a signal when the object moves. The electrical circuit (66) can include an active or passive radio frequency identification tag, at least the passive type of which is responsive to an externally generated alternating current electromagnetic signal such that the electrical circuit transmits a responsive signal for reception outside the object as the object moves through the conduit. A transmitter (38) can be provided to transmit into the conduit an alternating current electromagnetic signal, wherein the electrical circuit transmits its electromagnetic signal in response to the alternating current electromagnetic signal from the transmitter. <IMAGE></p> |
