Features of Programmable Logic Controllers Flashcards
What are three reasons why PLCs are more reliable than the hired-wired controls they replaced?
- Use of semiconductors
- Fewer parts
- No moving parts
- Rugged packaging
Why is a PLC system program printout more convenient than a schematic diagram for a hard-wired circuit?
A printout is easily and quickly made; no drafting is required
What does every PLC have that allows much diagnosis to be done without using a tester?
Plenty of indicating lights - a minimum of: one on each input, one on each output, one for power, one for low battery
What language is usually used to program PLCs?
Relay ladder logic
What type of control installation would not benefit from the use of a PLC?
One where control and troubleshooting are very simple
What type of long-lasting battery may be used to back up volatile PLC memory?
Lithium
What is the term for the connector into which a programming terminal is plugged?
A communication port
What is the main difference between an intelligent terminal and a dumb terminal?
An intelligent terminal can be used to key in a program off-line (where it is not communicating with the PLC)
Where may a hand-held programming terminal be preferred over a personal computer for PLC application?
Where it may be roughly handled
Where may a personal computer be preferred over a hand-held programming terminal for PLC application?
Where it is necessary to see as many program rungs at once as possible. When a large program is being edited or while troubleshooting
Downloading is a process that uses a programming terminal to copy a user program into the __________ memory
PLC
A computer that is “on-line monitoring” a running program allows the user to determine which outputs are on and which are off. How is this achieved?
The CRT shows an output that is on with highlighting of some sort, usually reverse video
Why print out a PLC program if it can be viewed on a CRT?
It is quicker to visually scan hard copy than to scroll through a program on a CRT. Planned changes can be red-pencilled onto the printout before making changes
