Using a normally open allows many possible faults that would disable the stop circuit.
An Emergency Stop system should also always be based on NC contacts, and if there is any possibility at all of an injury being caused by a machine the ES system should be a hardware type separate from the PLC, so PLC problems cannot disable it.
ES systems should also be self-testing to ensure no single fault can disable the ES system.
In machinery that can cause significant injury, the ES system should be 'double loop', using two NC contacts on each switch and two separate circuits, so a complete failure of one ES loop/circuit does not prevent the ES operating.
A normally open contact in to a PLC would be extremely unsafe & could be disabled by bad connections or wiring faults.
It would not be legal on any machine that actually needed an Emergency Stop function.
PLC – SCADA – DCS Training institute in Chennai – Wiztech - 9940426826
PLC – SCADA – DCS is the best technology in electronics field. It is a grooming field in world technology. It consumes more job opportunity in industry. Wiztech is the best PLC – SCADA – DCS Training institute in Chennai Wiztech provides advanced diploma Automation training with international certification and 100% practical. Wiztech provides FREE Accommodation and free Placement service also. So if you want to do PLC, SCADA, DCS and Embedded, VLSI Training just enquire in Wiztech.
Wiztech Automation Solutions pvt ltd.,
Ph: +91 99404-26826, 044-26209369.
102, W-block, 2nd & 3rd floor, 2nd Avenue,
Anna nagar roundana,
Anna nagar,
(Near Indian bank)
Chennai – 600 040.
Tamilnadu.
Mail us: wiztechtraining@gmail.com
Web: www.plctraininginchennai.net
If there's a fault, the off switch won't work. Fill in your own scenario of killer robots, rotating shears etc.
Ask yourself how would you complete a circuit if one of the wires was broken or if you didn't have a battery?
Can anyone identify and briefly explain the dangers posed by the 2 following scenarios?
The stop button on a plc motor program has been set up using an XIO instruction as the stop bustton has been installed using a normally open contact. During normal production when the motor is running, a fault develops which causes the fuse supplying 24Vdc to the PLC input card to blow
An E stop is wired as a normally open contact to a PLC input. Over a period of time vibration in the production area has caused the cable between the E stop and the PLC input to become disconnected.
Any help would be much appreciated.
