Found in American documentation from the 90s, this circuit uses a high voltage relay and has no grid isolation. The high values of R1 and R2 prevent the shock when it touches the sensors.
We find this circuit in American documentation from the 1980s. The accuracy of the circuit depends on the...
The circuit shown was found in a 1967 RCA manual. Modern equivalent components can be used. The...
Figure bellow shows how one of the two separated counters found inside the 4518 is used as a...