1. n. [Formation Evaluation]
The reactive (X) signal, or that part of the alternating signal at the receiver of an induction logging tool that is out of phase with the transmitter current. This signal, also known as the quadrature signal, is less sensitive to formation conductivity and must be separated from the R-signal, which is the main or, in older tools, the only source of the induction log. In a simple two-coil array, a large component of the X-signal is caused by direct coupling between transmitter and receiver coils. This direct signal is largely eliminated by use of a bucking coil. The X-signal provides a first-order correction to the skin effect of the R-signal.