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.