ESD is part of PLC or PLC is part of ESD???

Can any body clarify which is part of what???

ESD (Emeregency shut down) is part of PLC (Programable Logic controller) or

PLC is a part of ESD???


mvr

Define ESD.

My first thought is electrostatic discharge but not sure how that would apply.

ESD definition

Esd is emergency shut down. PLc is Programable logic controller.
Now answer my question dear.

chop347

Have seen many cases where the ESD is written in the program. This is a bad idea as I have seen plants where the plc has frozen up and when they went for the ESD nothing happened. Always wire your ESD as a stand alone system.

I usually try to design a system where the PLC tries to shut down the system in an orderly fashion, but a hardwired system will shut the system down a certain amount time after the PLC has had the option to do so as a backup. If the system is not very complex and does not require any coordination among the components I may just use the hardwire shutdown system. I never use PLC only shutdown on systems where there are safety issues.

Emergency shut-down can have different categories, or levels, to determine whether the shutdown is instantenous or controlled, controlled meaning allowing the machine time to come to a complete stop then disengaging by electromechinal means.

Just a couple of years ago standards, in the US, stated that operation of ESTOP could not depend on electronic logic, software or hardware, or commands over a network or communication link.

Some of that has changed with the use of Safety PLCs etc, where it may be allowed to use the plc to control the machines stop...it depends.

To answer the original question to the best of my ability; ESTOP is a procedure to bring a machine (system) to a halted condition, in many cases this will be a hardwired solution BUT it may be possible (now) to have a PLC incorporated into that procedure.

I just put in a system where there are several ESD-initiators in the PLC. For the ESD, a solenoid to pneumatics. The output to the ESD solenoid is held on by non-latching logic. If the PLC fails, the ESD occurs.

If you make the ESD fail-safe, there isn't any reason why you can't drive it with a PLC.

Actually, several systems I maintain have a "run permissive" for equipment hardwired to a PLC output, set up the same way.

It's pretty common.

Within the last 3 days, I had an AB output card that had one output stuck on even though it wasn't activated and on the exact same card, had an output that would not turn on even though the logic had it on (and the light on the card was on). I'm not sure how you could make something like that "fail-safe".

I'm not sure how you could make something like that "fail-safe".

Click to expand...

I agree!

All components should be safety rated!!!

chop347

As always with stuff like this, it is the what if. So very rare now a days to see a plc completely freeze up. But if you are using a poor model instead of top qualitly. It does happen. Where the plc will lock up with all i/p and o/p in there last state. So if you removed your esd i/p the plc wont see it and shut the system down. Work on systems where we have different levels of shut down. If we want a complete black out. Thes ESD buttons are all hard wired fail safe. Just another idea as many out there.

Mr.Chop my questions is

a system having other sequential logics and start stop and cut in logics and shut down logics is called as ESD or PLC.

some says esd is part of plc and some says plc is a part of plc...can u give a clarification...

dear Rsdoran,
a system having other sequential logics and start stop and cut in logics and shut down logics is called as ESD or PLC.

some says esd is part of plc and some says plc is a part of plc...can u give a clarification...
mvr

good practice. thank you.

I used a AB ControlLogix PLC with SIL2 rated hardware. I programed my ESD procedures in it. I used DO modules so that if I cut the power to the module, all valves/breakers would fail to the failsafe position in the de-energized state. I then positioned E-stop buttons thoughout the facility so that hitting the E-stop would cut the power to the DO module and therefore all field instruments fed from it... dropping them into the ESD positions. I also had a DO from another module in series with the E-stop. That way I could have emergency conditions.. high pressure etc, trip the DO using internal logic. Of course the case that was mentioned where a DO gets stuck on is possible but the E-stop will over-ride that case... plus the Modules are safety rated.

Can get expensive but it depends on what standards you need to achieve. If you read some of the SIL type information, you can place two instrument in series using different PLC circuits but that gets even more pricey.

Gadz

maya3369 said:

Can any body clarify which is part of what???
ESD (Emeregency shut down) is part of PLC (Programable Logic controller) or
PLC is a part of ESD???
mvr

Click to expand...

Neither, in my opinion.
Emergency shutdown (aka safety circuits) has to have nothing with PLC logics but to be hardware circuits.
However, the entire circuit may be powered from PLC output.
This way the PLC can shutdown the machine, but never can power it up again alone.