Seal in run circuit.

I think you guys should post some electrical drawings to clarify what you are explaining.

robw53 said:

when you say put the outputs from the safety relays in series do you mean 13 & 14 and 23 & 24 in series then take them to one I/P to the master and then the same on the other safety relay and feed them outputs to the second channel on the master?

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No, the two channels would be used exactly like you would an E-stop with two contacts. So, 13 & 14 of the first relay in series with 13 & 14 of the second relay then feeding into one channel of the master, while 23 & 24 of the first relay are in series with 23 & 24 of the second and feeding into the second channel of the master.

robw53 said:

to me this [door contacts and e/stops feeding small relays that all the N/O contacts are in series and feed the safety relay] isnt such a good idea apart from been easy to see which one is at fault, what do you think??

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I agree completely. This is a poor practice at best, and simply unsafe if they have chosen to not use safety rated devices, too. I believe door contacts and E-stops should be monitored directly.

robw53 said:

the two mechanically guided relay contacts do you mean wire each of the two MGR in series with the E/Stops input to the safety relay and the other MGR in series with the Door safeties or would you wire them to the terminal outputs from the slave safety relays that feed the master safety relay?

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When I wrote about "two MGR's" from one device, these are connected to the outputs of the Master. These two are where you make and break the E-Stop Controlled Power to the rest of the machine. From the PLC, there is only one MGR. Two NO contacts from this one relay are used, once again the same way you would an E-stop PB with two contact blocks, in the circuit that feeds the Master. When finished, terminals 13 & 14 will have three devices wired in series between them; the first channel output of the E-stop PB safety relay, the first channel output of the Gate Switch safety relay, and one contact of the MGR from the PLC. Terminals 23 & 24 will be wired similarly with the second channel outputs and the other MGR contact.

I think my wording (that you quoted) was poorly written. Does this make it clear?

Steve

I would post drawings, but unfortunately I am at home (off this week, WOOHOO!) and don't have my documentation at hand.

Steve

yes that makes more sense 12, 13 from one safety relay to 12,13 of the second and so on, thats clear now.

well i am glad you agree with me about the use of small relays makes me feel like i am on something of a similar wave length.

i understood the bit about two MGR from the master to use as a high current switching for other such devices which a pilz couldnt handle, my mistake i thought that you also had two MGR from the PLC O/P not two contacts

so just to clarify you would have in series the contacts 13 and 14 from both safety relays and then through the N/O contacts of the MGR and then to the input of the master safety relay channel 1 and the same with all 3 devices using terminals 23 and 24 and the second pair of contacts from the MGR to channel 2 of the safety relay then. then like you said a hard wired reset, one other thing i would use the reset to reset all the 3 safety relays would you agree with that or is there a reason some may have to be auto reset.

i do understand everything you say here but if you happen to have a wiring example of this at work i would be greatful of a copy for future reference as i am new to this so need to get alot of stuff which you would see as elimentary into my head, i am fine programming RS500 i am just heading into the 5000 and communication field its just things like how to do something in real world applications that i need to learn and this was an excellent one to pick as safety comes top on mine and am sure your priority list.

yes i did struggle to understand that bit i do think that it maybe to do with in the us compared to the UK you use different terminology for different things.

so thankyou for taking time to explain and if you know of any information or documentation that would be helpful to someone who wants to progress into a systems integrator/PLC programmer hopefully in the great USA one day. then please let me know

Rob

one thing i would love to know is were do you learn all these rules and regs, they must be something out there with the regs on this sort of thing, i mean how did you guys learn all the stuff you did to become pro's at it?

Rob

sorry i do have another question while we are on the subject, when i was at Allen bradley we did go through the use of MCR in the program but they don't go through the use of them in a factory or how you stand from a safety point of view, would you use them in the program to isolate outputs or would you not go to the trouble as i have heard they can be a pain in fault finding.

Rob

The MCR instruction is a PITA in a PLC program. I don't like them at all. Unless you are pressed for memory, it is better to put an XIC instruction on every rung you want to drop out. But don't confuse this with personnel safety. The PLC program should be written such that it protects the equipment, and so that it doesn't do things that are unexpected, but for peoples' safety, keep it in hardwiring.

cheers once again paul

Rob

so is it "MCR" - or is it "MCR" ... ??? ... (Genesis 11:7) ...

Greetings to all ...

there are TWO separate "things" being discussed here – and a careful reading of the thread shows that some of the newcomers are misinterpreting what is being said ... unfortunately, the TWO things both share the same initials (MCR) and thus many programmers and technicians confuse the terms with one another ...

(1) MCR can be used to mean "Master Control RELAY" ...

(2) MCR can also be used to mean "Master Control RESET" ...

secret handshake: they are NOT the same thing – but a LOT of people confuse them ...

what makes it especially confusing is the fact that there are only THREE LETTERS that are different in the two terms ... specifically: reLAY and reSET ... (yes indeed, some sadistic so-and-so went out of his way to make this confusing) ...

to clear this up, I suggest that you start reading at page 66 at the following link for an SLC system's HARDWARE User Manual:

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1747-um011_-en-p.pdf

keep going and be sure to notice page 69 which gives a wiring diagram that might be helpful for the discussion at hand ... notice that this shows a HARDWIRED DEVICE "MCR" Master Control RELAY ... specifically, it does NOT show the LADDER LOGIC instruction "MCR" Master Control RESET ...

keep in mind that THIS type of MCR (specifically, a HARDWIRED Master Control RELAY) is a "safety related" type device which can be used to turn stuff OFF by interrupting the line power to various field devices ...

now then ... next take a look at page 132 at the following link for an SLC system's LADDER LOGIC INSTRUCTION SET User Manual:

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1747-rm001_-en-p.pdf

notice that this entry discusses an "MCR" Master Control RESET which is an INSTRUCTION located in the PLC's LADDER LOGIC program ... specifically, the item being discussed at this link is SOFTWARE ... more specifically, it is NOT the same thing as a HARDWIRED "RELAY" ... and MOST specifically, this type of MCR (a Master Control RESET instruction in the ladder logic program) is NOT suitable for use in safety related situations ...

going further: the way the term "reset" is being used in the text linked just above, literally means to have any affected OTE instruction "GO AND WRITE A ZERO INTO A BIT/BOX" ... or at least that's the way I'd insist that the OTE's operation be expressed in one of my classes ... the trick is that the apparently simple word "reset" means many different things to many different people ...

so ... some of you guys are TOTALLY CORRECT in what you're saying – but some of the other guys are TOTALLY MISINTERPRETING what they're reading ...

I hope this helps ... party on ...

thankyou for that ron, to clear things up i was talking about the MASTER CONTROL RESET within the ladder.

rob

robw53 said:

sorry i do have another question while we are on the subject, when i was at Allen bradley we did go through the use of MCR in the program but they don't go through the use of them in a factory or how you stand from a safety point of view, would you use them in the program to isolate outputs or would you not go to the trouble as i have heard they can be a pain in fault finding.

Rob

Click to expand...

Rob

Do not use the mcr instruction in programs as okie said it is a PITA and is normally found in full stupidity programs. I have spent a great deal of time removing junk like this from programs. It will only make troubleshooting harder. IMHO the same goes for latch bits and sequencer instructions and in most cases indirect addressing also. Indirect addressing has it's place/need but 90% of the time it is used where it is not really needed and something more simple would have been better served.

Ron - Yes, thank you for that MCR explanation. I never understood there were two meanings for MCR. I always thought it meant Master Control Relay. Because of that, I suppose, I fall into the same camp as OkiePC and find them to be a PITA to use in a PLC - and therefore never use them.

RobW53 - I agree that the Reset PB should typically be used for all three relays. This is, IMHO, the best way to be sure the operator stays in control. As far as Auto-Reset is concerned, yes, there are occasions where using it makes sense, but in the examples we have been discussing so far, manual reset is best.

One example where I can see that an auto-reset makes sense is in a machine a light curtain must be broken by the operator to remove the finished product and a new blank set in place for the next operation. In this case, the light curtain is attached to its own safety relay with an automatic reset and a bypass around its output in the Master circuit.

Any time the machine is in its "Home + Finished" state, the bypass is enabled. This allows the operator to break the light curtain and reach in without causing an E-stop.

Once the operator is clear of the curtain (and it has automatically reset itself) he issues a two-handed "Cycle Start", the bypass is removed and the light curtain and its safety relay become part of the E-stop Circuit while the machine is in-cycle.

i was under the impression it was a bit of a PITA! would you used OTE and latch them with a XIC with the same address?

paul did give me a link to one of rons videos which explained the fact OTL outputs are retentative unlike the OTE

when you say indirect addressing are you refering to mapping the outputs to a binary (B3:0) for example

rob