Found in old documentation, this circuit has only the most difficult component to obtain the PUT. The sensors are electrodes placed in the reservoir. The circuit directly controls an AC power load.
This circuit is from National Semiconductor documentation. The operational amplifier is of the...
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...
This circuit, from an American publication of 1974, provides a 0.005% regulation with a variation of...