These controllers operate on the principle of electrolytic conductivity in liquids. A built-in sensitivity adjustment permits field tuning the instrument so that one model is suitable for most conductivity liquids. For instance the LL4 or LL7 may be adjusted to respond to either foam or liquid. Some controllers may be as far as 300 meters from the electrodes, and connections are made with unshielded cable.
The AquaMetrix design limits the voltage at the electrodes to 18 volts, and also limits the current even if electrodes are shorted. Some competitive controllers may require as much as 500 volts across the electrodes.