E Stop

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ptonsparky said:
Owner would like clamp to raise, and saw to raise when E-stop is pushed, the rest can remain in place. He has defined this as a safe position. Reasonable request.

Normally I would use the E-stop to remove power to input, outputs and any control relays involved. Never was involved with the air solenoids before.
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In my industrial controls / PLC work, we did not remove power to inputs, only outputs. Inputs were killed only if the PLC was powered down or an internal switch (actually a fuse) was used. If the application allows, I would use spring offset, single solenoid valves for clamp and "saw engage" so power off does the safe thing. We also used various "safety relays" or light curtains which may remain powered, but not usually closed or with contacts receiving power, in an e-stop condition.
 
I can see that I will need to leave the inputs active as well as some of the outputs.

We are not responsible for building the saw. Original project was to copy an existing control built by someone who knows PLC programming. Once we looked into the operation it became very obvious he had little electrical training otherwise. Firmware changes on the newer PLC and a different HMI opened up all sorts of options and I keep getting "Can you do this?" Generaly the answer is Yes but we may be running out of room for additional I/O if it keeps up.

Thanks for all the replies. As usual, a good learning experince and valuable infomation.
 
coulter said:
Could you give a source for this "requirement"? I don't know of any regulatory law on this subject.

Edited to add, "for the US."

carl
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Carl and yes these are US standards

ANSI B11.20; 6.7.1: System Emergency Stop
System emergency stop shall immediately initiate stopping action of those motions that pose an imminent hazard to
personnel. Resetting of the emergency stop shall not initiate, restart, or create any hazardous motion. A manually
operated emergency stop device shall be hard wired into the emergency stop circuit and shall function independently
from the programmable electronic system (PES).
NFPA 79: 9.2.5.4.1: Emergency Stop
Emergency stop functions provided in accordance with 9.2.5.3 shall be designed to be initiated by a single human
action.
 
ANSI B11.20 has been replace by AMT B11.20. I should have that one in a day or so.

Interestingly NFPA 79 appears to allow connection of E-stops through logic devices. With some exceptions (for VFDs) the final element should be an electromechanical device. So far, this "hard wire E-Stop requirement" is eluding me.

NFPA 79 said:
9.2.5.4.1.3 The emergency stop shall function as either a Category 0 or a Category 1 stop (see 9.2.2). The choice of the category of the emergency stop shall be determined by the risk assessment of the machine.
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9.2.5.4.1.4* Where a Category 0 or Category 1 stop is used for the emergency stop function, it shall have a circuitry design (including sensors, logic, and actuators) according to the relevant risk as required by Section 4.1 and 9.4.1. Final removal of power to the machine actuators shall be ensured and shall be by means of electromechanical components. Where relays are used to accomplish a Category 0 emergency stop function, they shall be nonretentive relays.

Exception: Drives, or solid state output devices, designed for safety-related functions shall be allowed to be the final switching element, when designed according to relevant safety standards.
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Also, I have not found any evidence that NFPA 79 or ANSI/AMT B11.20 carry the force of law.

still reading

carl
 
cschmid said:
...Can you post me a link for AMT B11.20. ...
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I don't have a link where you can see it with out a subscription. Maybe a college library.

cschmid said:
.... These regulations are enforced by agencies like OSHA. ...
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We have already had this conversation about citing your references. If you don't, its just an opinion.

cschmid said:
... The wiring methods are by the NEC....
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Okay, that's good. But I still don't know of anything in the NEC that requires a hard wired E-Stop.

cschmid said:
... where you are from?
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I live in a third world state the US treats as a colony -- Alaska. I tend to consider myself an American, Alaskan, US citiuzen - in that order:cool:

I'll get back after I read B11.20. I always try and do my homework before I talk.


carl
 
Hi Carl nice to meet you.

I quoted my source as listed below. I would assume OSHA would enforce but since I can not prove that it is an opinion. I guess I am not following what you are after here? I will check the age of our manuals. other wise this is what I am quoting and If I am wrong I will have learned something.

ANSI B11.20; 6.7.1: System Emergency Stop
System emergency stop shall immediately initiate stopping action of those motions that pose an imminent hazard to
personnel. Resetting of the emergency stop shall not initiate, restart, or create any hazardous motion. A manually operated emergency stop device shall be hard wired into the emergency stop circuit and shall function independently from the programmable electronic system (PES).

NFPA 79: 9.2.5.4.1: Emergency Stop
Emergency stop functions provided in accordance with 9.2.5.3 shall be designed to be initiated by a single human
action.
 
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