Page 425 - Programmable Logic Controllers, Fifth Edition - Mobile version

Volatile memory A memory structure that loses its information
whenever power is removed. Volatile memories require a battery Work cell A group of machines that work together to manufacture
a product; normally includes one or more robots. The machines are
backup to ensure memory retention during power outages. programmed to work together in appropriate sequences. Work cells are
often controlled by one or more PLCs.
W
Write Refers to the process of loading information into memory;
Watchdog timer Monitors logic circuits controlling the processor. can also refer to block transfer, that is, a transfer of data from the
If the watchdog timer, which is reset every scan, ever times out, the processor data table to an intelligent input/output module.
processor is assumed to be faulty and is disconnected from the process.
Word A grouping or a number of bits in a sequence treated as a unit. Z
Word length The total number of bits that make up a word. Most Zone The portion of a PLC ladder program that can be enabled or
programmable logic controllers use either 8, 16, or 32 bits to form a word. disabled by a control function.

406 Glossary

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