Question on emergency stop circuit
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Hello everyone. This is my first time designing a system from scratch. The system is for a rubber injection molding press. I have the PLC all put together, wired most of the programming done, and I am working on figuring out the emergency stop circuit now. My understanding is that when you hit the emergency stop button all functions of the machine will cease and cuts all power to everything except the controller and HMIs. I have 2 voltages, 24vDC which powers all inputs, and 110VAC which powers my outputs coming from the PLC.
My main question is, how are you able to have any sort of indicator telling the operator that the emergency stop has been pressed (such as stack light, alarm siren etc.) with out having some sort of output voltage going somewhere? Is it acceptable or common practice for this to be allowed? Our current machines were built with not much thought into these things and dont have any sort of indications that it has been pressed.
I currently have a pop up window on the hmi but thats it so far.
Thanks for your input and comments!
Talldude42,
I have an assumption that you are NOT designing a control system for a new rubber injection molding machine, but instead, are designing a new control system for an existing rubber injection molding machine. (Machinery modifier)
As we did in the past, we merely looked at the existing control system, and replicated it with newer components. The blind replacement with newer components, and replicating the electrical / hydraulic / mechanical design, while which achieves manufacturing requirements, leaves the end users at risk of injury.
You, and your employer, are MODIFIYING a Vertical Clamp Injection Molding Machine. Your company will be held responsible to make sure that the controls retrofit satisfies all applicable CODES and CONSENSUS STANDARDS applicable at the time of remanufacture.
Your original question was related to Emergency Stop terminating power to output devices. This comment indicates that current RISK ASSESMENT strategies are not being considered.
I am not trying to intimidate, conversely, I am trying to awaken, or heighten your awareness that this task is more than your responsibility, as a single individual, merely specifying electrical safety parts and deploying them. The entire machine control system electrical/hydraulic/mechanical, using TEAM based RISK assessment, and TEAM BASED risk abatement strategies.
There is an ANSI Document for Vertical Clamp Injection Molding Machines ANSI/SPI B151.29
There probably are numerous more ANSI / NEC / NFPA / OSHA / Etc… consensus standards applicable to your employers retrofit controls upgrade plans, your employer as owner of the machinery will be held responsible if the retrofit is not deployed to the industry consensus standards of the time of remanufacture.
Not trying to scare you off, actually, the opposite… all injection machines are aged, and the control systems are dying and obsolete. This is an opportunity to put new controls on, with an INCREASED and UP-TO-DATE SAFETY system.
Best regards,
Plastic