The HI 9920 is an ORP controller with a single set point for user selectable dosage of reducing or oxidising solutions. Any ORP electrode ending in a BNC connector can be directly attached to the controller. With proportional control, you can fine tune your treatment plant and minimise the use of chemicals. The proportional setting can be adjusted through the time cycle from 0 to 90 seconds and the band from 0 to 200 mV. The set point can be accurately adjusted through coarse and fine trimmers. A pump or electro-valve can be wired directly to the controller and be powered through the terminal.

In addition to the set point relay, the HI 9920 also provides for an alarm relay. The alarm is activated when the measurements exceed the operator adjustable threshold of 50 to 250 mV from set point. For extra security, a maximum dosing time from 1 to 10 minutes can also be set, after which the alarm is activated to signal an abnormality. The alarm configuration is alterable in a normally-closed or normally-open state to accommodate Fail Safe installations.

Any recorder accepting a 0-20 or 4-20 mA output can also be hooked up to the controller. Users can see the controller's status, even from a distance, by observing the dosage or alarm LED's. To speed up wiring, HI 9920 comes with extractable terminal modules. Once wired up, the compartment containing the connections is protected behind a fire-retardant ABS removable panel.