The HPD is a level controller which works with sensors fitted to the Polaris heater.

The sensor are Braude filaments which will not corrode in
even the most corrosive of solutions.

The controller operates by passing a small ac current through the
sensors which will detect the presence of a liquid.

If there is no liquid present the controller will default to the off position
and the heater will be turned off thus ensuring safety of the heater and the tank.

HPD supplied with controller and sensors fitted to a Polaris heater,
and is best ordered at the time of ordering the heater, so ensuring the sensors are correctly positioned.

It is possible to retrofit sensors where there is no other choice.