1 Week 11 SYSTEM SAFETY Matakuliah: Mechatronics 2 Tahun: 2005 Versi: 1.0/0

2 Learning Outcomes By the end of this session, students will understand the safety in building a PLC based system.

3 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

4 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.

5 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.

6 Unsafe Start/Stop Program 1) Improved Start/Stop Program using Overriding Stop 1) 1) Hackworth & Hackworth Jr.

7 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.

8 Safety Interlocks Most commonly used interlocks : –Interlock switch. –Pressure sensitive mat switch. –Light curtains.