System for recording a variable value, notably in a well, and for

Abstract

To acquire and record the variation of a value such as a pressure as a function of a parameter such as time in a sonde (10) lowered into a well (12), pressure measurements are made at equal time intervals, these measurements are digitized and entered in a nonvolatile memory selectively so as to maximize the accuracy of the pressure variation reading during the measurement period, while minimizing the memory volume necessary for this purpose. The selection of the acquired measurements for their recording comprises a data compression stage in which are eliminated the measurements which do not correspond to a variation in the slope of the pressure-versus-time curve greater than a predetermined threshold. The data compression is effected in a buffer memory in which each measurement has associated with it a deviation index indicative of the time interval separating this measurement from the following one in the buffer memory. This time interval amounts to a number of elementary time intervals which is always a power (n) of 2, n integer, and the exponent n is stored as the deviation index.