Week 11SYSTEM SAFETY Matakuliah : Mechatronics 2 Tahun : 2005 Versi : 1.0/0
Learning Outcomes • By the end of this session, students will understand the safety in building a PLC based system.
System Integrity • Environmental effects may cause premature failure of the system. • Complying with existing standards, e.g. National Electrical Manufacturers Association (NEMA) and International Electrotechnical Commissions (IEC). Some issues among others • Accidentally body contact • Falling Dirt • Wind blows dust • Falling liquid, lights splash • Submersion
Equipment Temperature Consideration • The life of an electronic device depends on the temperature at which it is operated under (inversely proportional). • Ensuring that the equipment is not overheated or exceeding the manufacturer’s specification is important. • Any protective enclosure will raise the temperature of the PLC. During the design process of the enclosure, measurement should be taken under the worst case conditions. • The use of cooling fans require screens/ filters to clean the air being drawn into the enclosure.
Fail Safe Wiring & Programming • Use more than 1 switch to start the system, e.g. 2 switches being pressed simultaneously to start will prevent the system to be accidentally started.
Unsafe Start/Stop Program 1) Improved Start/Stop Program using Overriding Stop 1) 1) Hackworth & Hackworth Jr.
Safety Interlocks • Personnel are prevented from making any physical contact with the equipment while it is active (energized). • Maintenance personnel however needs to have access on the equipment. • Monitoring access points ensuring that they are not opened while energized is important (or the equipment cannot be energized while personnel is inside). • Interlocks is used to provide this monitoring method.
Safety Interlocks • Most commonly used interlocks : • Interlock switch. • Pressure sensitive mat switch. • Light curtains.