Does anyone know exactly how many PLCs there are to a single power plant? Is there a PLC to monitor each variable (I.E. pressure, temperature, that kind of thing)?

-- Anonymous, November 25, 1998

Answers

It's kinda like asking how many computers are in a business. It will vary depending on the size and design of the data handling needs of the job at hand. A single PLC (Programmable Logic Controller) can monitor several inputs at once from different sources. They aren't specialized. If a sensor can generate a signal indicating it's condition, chances are you can monitor it with a PLC Hope this helped

Keith

-- Anonymous, November 27, 1998

Ben:

PLCs can be configured to monitor hundreds to thousands of points. Most of these points will be simple status indications based on contact closures or 4-20 milliamp analog inputs - ie dumb I/O. Modbus is an industry defacto standard protocol that lets PLCs talk to each other and to other intelligent instruments and devices - ie smart I/O. Here's where you might find non-compliant devices.

Usually a PLC will be dedicated to a subsystem with each of the subsystems reporting up to a higher level DCS or SCADA system. This level will have the most chance of being date aware.

Jim

-- Anonymous, November 30, 1998