CHAPTER 4Sensor Connections169Note: To find out which internal sensors your devices areequipped with, please refer to the user manuals of therespective devices.Logical Channels and Output ChannelsLogical channels and output channel are used at the A740 RTU.The A740 provides programmable sensor connections which arecombined as LC and OC connections.Logical channels are used for analog/digital sensors.Output channels are used for analog/digital actuators.For details see the A740 user manual.SDI-12 BusThe abbreviation “SDI-12” is an acronym for "Serial Data Interfacewith 1.200 baud". This standard communications protocol wasdeveloped particularly to interface battery powered recordingdevices with micro-processor based sensors designed for environ-mental monitoring. Unlike RS-232/RS-485 devices which usuallyrequire proprietary drivers for communication, the SDI-12 protocolensures compatibility between all sensors and loggers featuringsuch an interface. If you want to learn more about SDI-12, visit thewebsite of the SDI-12 Support Group , “http://www.sdi-12.org/”.The SDI-12 bus built into the A740 addNODE or usable with anadapter on A723 addITs and A733 addWAVEs is enjoying increas-ing popularity with manufacturers of low power sensors, particu-larly in the field of water quality monitoring. Many manufacturersof multi-parameter probes, like Hydrolab, YSI and Greenspan,already offer SDI-12 compatible probes.Note: The A506 SDI-12 Adapter makes A723 addITs and A733addWAVEs SDI-compatible. If you have SDI-12 sensors,attach the SDI-12 adapter and the respective sensors. Formore details about installing the SDI-12 adapter and SDI-12sensors, consult the corresponding users manuals.
