[en] Two basic types of transducers (with electrodeposition and different electric field configuration) used in fuel element tiahtness control systems are considered. Analytical expressions for determining the detector mean counting rate are presented. It is shown that the output signal of the first-type transducer with a localized electric field depends on the concentration of negative ions in a gas. At the same time the counting rate of the detector of the second-type transducer whose electric field embraces the whole volume of the decay chamber can be made, under certain conditions, independent of the concentration of negative ions in the carrier gas. Therefore it is recommended to use for quantitative measurements only transducers of the second type. It is stressed that for continuous measurements it is necessary to use transducer with several detectors which would measure in sequence the activity of nuclides in the same section of the collector