So far we have assumed that a PLC consists of a processor unit anda collection of I/O cards mounted in local racks. Early PLCs did tend tobe arranged like this, but in a large and scattered plant with this arrangement,all signals have to be brought back to some central point inexpensive multicore cables. It will […]
Output cards again require some form of isolation barrier to limit damage from the inevitable plant faults and also to stop electrical ‘noise’ corrupting the processor’s operations. Interference can be more of a problem on outputs because higher currents are being controlled by Computers and industrial
Computers and industrial control 25 the cards and the loads […]
Internally a computer usually operates at 5 V DC. The external devices (solenoids, motor starters, limit switches, etc.) operate at voltages up to 110 V AC. The mixing of these two voltages will cause severe and possibly irreparable damage to the PLC electronics. Less obvious problems can occur from electrical ‘noise’ […]
The PLC’s from Omron can be connected to various peripheral equipment. Each device requires its own cable layout. Only the more common cables are shown here.