Abstract: The disclosure relates in general terms to a sequence of automatic operations, with which a control loop is associated. By momentarily substituting a monitoring loop for this control loop, free-frequency auto-oscillation is set up in the sequence of automatic operations, and, since the monitoring loop comprises not only a gain amplifier but also a pure phase shifter, this setting-up of auto-oscillation is repeated successively at different frequencies. The device is applicable to the monitoring of any industrial plant for the purpose of regulating it.