Remote I/O Digital - do you use "blue hose" for digital I/O?
Many Allen-Bradley PLC-5 processors are now being upgraded to use newer ControlLogix processors – while still keeping in place (at least temporarily) the plant's reliable old "1771" style I/O hardware - and all of its installed wiring.
At the ControlLogix end of the line, a 1756-DHRIO "bridge" module provides a means of connecting the existing cables (known as "blue hose") to the new controller system.
This common situation presents some serious challenges to the maintenance crew. One specific issue is that the terminals and the LEDs on the older "1771" style input and output modules are numbered using OCTAL addressing. The ControlLogix system uses DECIMAL numbering instead.
This is such a common source of confusion, that each student in our Boot Camp classes will set up a DHRIO module through a series of hands-on exercises on Monday afternoon.
Reference material on Allen-Bradley's website for 1771-ASB
Reference material on Allen-Bradley's website for 1771-OAD
© Copyright - R.H.Beaufort - Charleston, SC – Updated: October 29, 2013