LAD: Ladder Diagram
Цель: Изучить тему «LAD: Ladder Diagram» 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
LAD visually resembles relay circuits. Contacts represent conditions, coils represent results. Normally open contact is true when bit=1; normally closed logical contact is true when bit=0 - this is logical representation, not necessarily physical contact type.
Series and parallel
Series contacts implement AND, parallel branches OR. Negated contact implements NOT. This makes LAD intuitive for electricians and interlock logic.
Seal-in circuit
START contact in parallel with Run latch and series STOP/permissives creates self-hold. In PLC better also implement explicit state and fault handling, but concept remains foundational.
Практическая работа
Write LAD logic for motor: start pushbutton, stop, overload healthy, level permit. Motor stays running after Start release. Add fault reset concept.
Самопроверка
• Series contacts correspond to what logic?
• Parallel branches?
• What is seal-in?
• Is NC LAD contact same as physical NC?
• Why permissives series with run logic?
Что нужно запомнить
- Contacts represent conditions, coils represent results.
- Normally open contact is true when bit=1; normally closed logical contact is true when bit=0 - this is logical representation, not necessarily physical contact type.
- This makes LAD intuitive for electricians and interlock logic.
- START contact in parallel with Run latch and series STOP/permissives creates self-hold.
- In PLC better also implement explicit state and fault handling, but concept remains foundational.