[en] A detector intended for use in automatic process control of substance composition is described. The detector is based on the element absorption jump X-ray analysis and employs semiconductor devices and A 108 decatrons with the exception of the reverse counter which uses reverse decatrons of a new type. The fully transistorized non-displayed counting decade circuit has a resolution time of 1 msec. The clock of the timer has four fixed frequences for 2, 5, 10, and 15 min measurement intervals. The results of measurements are displayed on the digital readout and on the analog data plotter