Archive for the 'PLC Hardware' Category

Physical Components vs. Program Components

Thursday, March 13th, 2008

When learning PLC programming, one of the most difficult concepts to grasp is the difference between physical components and program components. We will be connecting physical components (switches, lights, relays, etc.) to the external terminals on a PLC. Then when we program the PLC, any physical components connected to the PLC will be represented in […]

Typical system components for a modularized PLC

Wednesday, March 5th, 2008

1. Processor. The processor (sometimes call a CPU), as in the self contained units, is generally specified according to memory required for the program to be implemented. In the modularized versions, capability can also be a factor. This includes features such as higher math functions, PID control loops and optional programming commands. The processor consists […]

PLC - Remote I/O

Sunday, March 25th, 2007

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 […]

PLC Output connections

Wednesday, March 21st, 2007

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 […]

PLC Input cards

Wednesday, March 21st, 2007

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’ […]

Omron PLC cable layouts

Saturday, March 17th, 2007

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.