Stability, feedback sign и runaway
Цель: Изучить тему «Stability, feedback sign и runaway» 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
Negative feedback corrects deviation; positive feedback amplifies it. Wrong controller action can turn intended negative feedback into positive: temperature low -> controller closes heating valve -> temperature falls further -> controller closes more.
Stability margin
Stable loop returns after disturbance. Marginal loop oscillates. Unstable grows. Physical limits may stop growth, creating limit cycles or saturation, but process can become dangerous before that.
Практическая работа
For heating valve with positive process gain determine whether controller should increase or decrease output when PV below SP. Then consider cooling valve with negative process gain.
Самопроверка
• Что такое negative feedback?
• Что такое positive feedback?
• How wrong action causes runaway?
• Что такое stable loop?
• Why limits don’t make instability harmless?
Что нужно запомнить
- Negative feedback corrects deviation; positive feedback amplifies it.
- Wrong controller action can turn intended negative feedback into positive: temperature low -> controller closes heating valve -> temperature falls further -> controller closes more.
- Physical limits may stop growth, creating limit cycles or saturation, but process can become dangerous before that.
- For heating valve with positive process gain determine whether controller should increase or decrease output when PV below SP.
- Then consider cooling valve with negative process gain.