MicroLogix: A Powerful, Low-cost RTU for SCADA Applications

The entire MicroLogix line of micro-PLCs includes the DF1 Half-Duplex slave protocol. This open network protocol enables MicroLogix controllers to communicate as responder (slave) nodes on DF1 master/slave networks that support up to 254 responder devices with a single initiator (master). With an average low cost price for discrete controllers, MicroLogix is a very cost-effective remote terminal unit (RTU) solution.

The DF1 Half-Duplex protocol works well in SCADA (Supervisory Control and Data Acquisition) applications such as water/waste water, power, and oil and gas. This enables a supervisory controller – such as an SLC 500, a PLC 5 or a personal computer – to poll DF1 Half-Duplex responder nodes to see if they have any data to transmit, to request specific data, or to download data.

This communication link can be made through a leased telephone line, radio modem or satellite link.

The MicroLogix provides fast and robust local control, with high-level math, data handling and specialty instructions. The new communications enhancements enable the MicroLogix to apply its intelligent local control capabilities as a very cost-effective RTU. The MicroLogix is one of the only micro controllers that offer this capability for such a low price. Many other SCADA solutions use a dumb terminal at the remote site that simply reports input status to the supervisory controller and updates outputs, but is incapable of any local control–the MicroLogix provides that smart local control.

DF1 Half-Duplex is a unique SCADA-type network that allows responder units to send data to other responders through the supervisory controller. This means MicroLogix controllers can exchange data with one another without any programming required in the initiator. This brings even more power and flexibility to a MicroLogix SCADA solution.Combined with the MicroLogix's communications capabilities, Compact I/O analog modules open up tremendous opportunities for SCADA applications.