Neptune Systems PM1, pH or ORP, Temperature, I/O Expansion Box. The first expansion module, the PM1 (shown above) , with a pH or ORP, temperature, and 6 digital inputs. The PM1 features are: * Monitor/Control pH or ORP, and temperature. * 6 digital inputs for float switches, water on floor sensors, pressure sensors, etc. * Full datalogging support in Apex Base module. * Up to 240 AquaBus modules can be added to the Apex system. * Plug and Play. Automatically recognized when installed into the system. * Two AquaBus connectors for flexible expansion via AquaBus * Led Status Indicator * Upgradeable firmware. * Compatible with Apex and Apex Lite systems. * Galvanic Isolation for accurate and reliable probe readings. * Comes with 3' AquaBus cable.