In order to operate a reactor, many variables have to be measured and monitored. Some of them are considered to be vital for the safety of the reactor, and their measurement has to be fast and reliable. What follows is a description of the technological options actually used to measure, process, display and record the variables in research reactors.

In research reactors the neutron flux has to be monitored from a low level to maximum power level. The detected flux is normally subdivided into three intervals, source range (below 10⁴ nv, equivalent to 10^-3 percent of nominal power), intermediate range (from 10³ to 10⁹ nv, or 10^-4 to 10² percent of nominal power), and power range (from 10⁷ to 2x10⁹ nv, or 1 to 200 percent of nominal power) as shown in Table 1. In the source range interval, due to the low rate of events occurring within the detector, pulse counting mode is traditionally used, whereas the current mode is adopted in the intermediate and power range intervals. The following equipment is currently available for detection and measurement of the neutron flux in the above three intervals.