This resistance meter was found in an English documentation from 1989. The operational amplifier admits an equivalent and the transistor can be a BC558 or BC559.
The diagram, obtained in an old European documentation, shows the ways to trigger and to shut down...
In the figure we have a three-phase AC motor control for voltages up to 600 V or 1200 V depending on...
This shield circuit can serve as a basis for a digital mixer or simply for a switch without noise...