Timers, counters and edge detection
Цель: Изучить тему «Timers, counters and edge detection» и закрепить её практическими заданиями и самопроверкой.
2 акад. часа чтение и разбор теории, решение задач, работа со схемой или виртуальным стендом и проверка понимания.
Основной материал
TON on-delay output becomes true after input remains true for preset time. TOF delays off. TP generates pulse. Exact names vary by PLC but concept standard.
Timers in interlocks
Valve commanded open; if OpenLS not true within 10 s -> fault. Motor start: wait 2 s before checking run feedback to allow contactor acceleration.
Edge detection
Rising edge creates one-scan pulse when condition changes 0->1. Needed for increment counter once, logging events or toggles.
Counters
CTU counts rising events. Use retentive behavior carefully; count may need reset on maintenance but not power cycle.
Практическая работа
Develop logic counting packages from photoeye. Add debounce/edge detection and stop conveyor after 100 packages.
Самопроверка
• What is TON?
• Why edge detection?
• What is one-scan pulse?
• How counter increments correctly?
• What is retentive data?
Что нужно запомнить
- TON on-delay output becomes true after input remains true for preset time.
- Valve commanded open; if OpenLS not true within 10 s -> fault.
- Motor start: wait 2 s before checking run feedback to allow contactor acceleration.
- Rising edge creates one-scan pulse when condition changes 0->1.
- Needed for increment counter once, logging events or toggles.