PLCs, DCSs & Controllers


Robot solution saves PLC inputs

November 2000 PLCs, DCSs & Controllers

A robot application used for control and interfaced to a PLC for all of its functionality required an upgrade to provide additional safety for robot movement. Eight inputs had to be monitored and an interlock had to be provided to prevent any movement of the robot arm unless all eight inputs were closed.

The control PLC would have had to be upgraded at considerable cost, as there were no available inputs for the task. Additional programming would have been needed to provide the full interlock functionality, with alarm outputs with indication for operators to diagnose malfunctions.

Omniflex's Omni-8u alarm annunciator, a panel-mounted eight input device that accepts digital inputs, has on-screen fault indication per channel and repeat outputs for interfacing to PLCs. This provided a simple solution, requiring no PLC upgrade or programming at all. Omni-8u is packaged in a compact DIN standard 96 x 144 mm housing and features built-in test, acknowledge, silence and reset pushbuttons on the front fascia.

All eight interlock digitals were input to the Omni-8u which was set up to provide a single Group Alarm which only turned on when all eight inputs were closed. The added bonus with this solution was that if any of the inputs jammed, the Omni-8u showed exactly which one, on its built-in display.

The whole application turned out to be much more convenient than upgrading the PLC with additional inputs and also easier than programming the PLC to do the interlocking and drive external display lamps to pinpoint faults. The Omni-8u offers a choice of standard alarm sequences and one of these 30 was perfect for this application.

Making up a legend for the Omni8-u was easy. Legends are printed from a laser printer onto a single transparency sheet and inserted as a single sheet under the faceplate. The Omni-8u conforms to the IEC environmental specifications for vibration, shock, temperature, humidity and human safety on electrical parameters. It is protected against EMI and has controlled EMC emissions.



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