looking for insite

Here is a program I wrote. Just want alittle feed back on it, or any suggestions. the file pic is attached. It will be on a AB micro logic or a SLC 5/05.

What sort of insight are you looking for ?

I'll go ahead and make the first and most obvious one: A general purpose (non-Safety) PLC cannot be an emergency-stop device. While your program doesn't exclude the use of a safety relay and appropriate E-Stop, pull-switch, and master control relays, it's clear enough that you are evaluating "safety" conditions before running the machine.

It's fine to logically prevent devices from attempting to start when the feedback from the safety system indicates its' been tripped and not reset, but you cannot rely on an ordinary PLC for a safety function.

Setting that aside as a major separate discussion, a couple more comments:

1. I prefer not to use examination of an Output as a pre-condition for other logic. If I can, I use the same set of Input conditions or I use an intermediate logical coil (B3:x/y) to indicate a combination of inputs or another system condition.

For example on Rung 3, you use the System On output as a rung condition, where you could just as easily have used the System On input address. While it's logically equivalent, I prefer to use Inputs as rung conditions when I can.

2. I think you have I:1/12 mislabeled: that should be "Stop PB Feed Hooper". Is this a "hopper" or am I unclear on your industry terms ?

3. I think this is meant to be a manually sequenced start program, where you must push the buttons to start the Picking Belt, the Trommel, the Infeed Belt, and then the Feed Hopper in order.

There are stop buttons to stop each device individually, but it looks like the only thing that will stop them all is the "E-Stop".

Generally I like to have a "System Stop" button that is not the same as the E-Stop. Sometimes it stops things in sequence, or ramps them down from full speed, and sometimes it behaves just like the E-Stop except that it doesn't dump power to every device in the system.

the e-stop will kill all control power even to the PLC. Yes I mislabeled I:1/12. and hooper is misspelled. This program is just a rough draft for say. It is for work. I did it at home to get me started. thanks for the insite.

Actually I don't kill *all*power: I strongly prefer that the PLC remains running and the inputs are active. That allows me to do things like log the time and date of an E-Stop event, and to run indicators that tell the operator which emergency device (button, pullcord, light-curtain, etc) have been pressed.

Emergency stops are a whole new world these days; the EU can't go more than a couple of years before planning a whole new stack of regulations, and North America dawdles along behind them, led by a pack of plaintiff's attorneys.

Your program looks sensible and straightforward.

A question about the Horn: it looks now like it will sound for 5 seconds before the Picking Belt starts, but only if you're starting the system in Auto mode.

Do you prefer to have a "honking" signal, or do you want a solid 5-second horn ?

I always preferred 1/2 second blasts because it helped me visualize how long before the system started; I didn't have to count "one-mississippi, two-mississipi" during the horn to know when the conveyor would start, just count "one, two, three, go".

You probably have standards for this sort of thing at your workplace.

I want a soild 5 to 10 seconds on the horn. I worte it on logixpro software. you can not change the pre from 0.1 to 1. I am going to add current transformer for the sequence conditions in auto mode. also added what ever my bosses and production would like to see for the machine.

What I always do is connect all the e-stops in series using the NC contact and wire it to a relay. I then use the relays NO contact as the input to the PLC. The relay also cuts the power to certain drive components but not the PLC system. I also monitor each e-stop using a NO contact connected to the PLC input to enable the operator to know which e-stop has been activated by displaying a message on the fault display. Another thing what confuses me is the Auto/Manual selector on rung 5. Is this a 3 position or a 2 position selector? If its just 2 position, I assume you wont need the auto/manual inputs for rung 5 as either one would be ON at any time. It only makes the rung longer without serving its purpose. hope i got this one right...

the auto/manuel switch will be a 2 position. I am not for sure what you mean by not needing the auto/manuel inputs.

jtashaffer said:

Here is a program I wrote. Just want alittle feed back on it, or any suggestions. the file pic is attached.

Click to expand...

I agree with all of Ken's comments. The electrical design and safety are always primary considerations especially for those beginning in the field. And he is giving you some very good basic practices to follow for using internal bits.

jtashaffer said:

It will be on a AB micro logic or a SLC 5/05.

Click to expand...

Then you should get the free version of RSLogix500 at least and write your program with it.

Heck, you can even get a free emulator nowadays.

So, you can test the code, and then go in and force stuff off and see what happens...try to make it "mess up" all without turning a tool or risking damage and downtime.

A program this short will leave plenty of memory available for using internal bits and expanding the structure of your logic even in the lowly workhorse 1K ML1000.

I would also add that for inputs, in the description, name the device type and describe its ON state. Use common symbology and don't make the comments wide. I prefer to truncate the length manual inserting CR, rather than to mess with the default symbol length in RSLogix500. But whatever you do, don't use the exact same comment for two different addresses.

jtashaffer said:

the auto/manuel switch will be a 2 position. I am not for sure what you mean by not needing the auto/manuel inputs.

Click to expand...

On rung 5, you do NOT need either of the Start / Manual inputs because one of the 2 will always be made. Basically, the 2 inputs being in parallel like that serves no purpose whatsoever. Of course, you will need them elsewhere in the program because they do serve purpose on the other rungs.

And I will second Ken's response. DO NOT kill the power to the PLC. Yes, you do need to break the power going to the outputs, but you want the PLC to stay on. Think for example that you have a machine with 5 ESTOPS on it. Someone presses 1 and you kill the PLC...If you have a machine with an HMI on it, you can display to the operator which ESTOP was pressed. If you kill the PLC, you can't do that. This is just one reason out of many for NOT killing the PLC.

Viks said:

What I always do is connect all the e-stops in series using the NC contact and wire it to a relay. I then use the relays NO contact as the input to the PLC. The relay also cuts the power to certain drive components but not the PLC system. I also monitor each e-stop using a NO contact connected to the PLC input to enable the operator to know which e-stop has been activated by displaying a message on the fault display. Another thing what confuses me is the Auto/Manual selector on rung 5. Is this a 3 position or a 2 position selector? If its just 2 position, I assume you wont need the auto/manual inputs for rung 5 as either one would be ON at any time. It only makes the rung longer without serving its purpose. hope i got this one right...

Click to expand...

Hi Viks,
This method was ok 20 years ago - But as has been said in this post
the current legal issues require extremely carefull and documented risk assesmsnt of a safety setup of any description.
the type you have suggested here is now considered virtually unsuitable for any safety application.

I agree with Ken in not dropping power to the PLC or HMI devices.
The Ouput power to any drive or driven device should be dropped.
But this is subject totally to the machine's integral design.
i.e. total safety system requirement.

Ken Roach said:

1. I prefer not to use examination of an Output as a pre-condition for other logic. If I can, I use the same set of Input conditions or I use an intermediate logical coil (B3:x/y) to indicate a combination of inputs or another system condition.

For example on Rung 3, you use the System On output as a rung condition, where you could just as easily have used the System On input address. While it's logically equivalent, I prefer to use Inputs as rung conditions when I can.

Click to expand...

In general I would agree with this although I think it's fine to use outputs as input conditions on a limited basis.

For example, if I am turning on a output that controls an interposing relay for a motor starter, I sometimes use this condition in series with the feedback from the aux. contacts of the starter to initiate a pump motor failed alarm.

iant said:

Hi Viks,
This method was ok 20 years ago - But as has been said in this post
the current legal issues require extremely carefull and documented risk assesmsnt of a safety setup of any description.
the type you have suggested here is now considered virtually unsuitable for any safety application.

Click to expand...

Assuming Viks meant a safety monitoring relay, I believe this method is still viable depending on the severity and frequency of the hazard. I do agree a risk assessment is required for all cases under the requirements.

yep - your right dkohio - But I didn't read Viks entry that way
Just this old buggers way of reading

I was keeping it simple
those who understand safety requirements dont need it reitterated constantly

I want a soild 5 to 10 seconds on the horn.

Click to expand...

You may want that, but if you were a guy working around that horn, you might be tempted after the 1000th startup to take a hammer and silence it forever. Horns mysteriously get hit by forklifts, stepped on by heavy boots, even though they are 30 feet in the air, and horn wires get cut somehow.

Making horns sound in an on-off cyle like Ken said is much easier on everyones ears and tempers. It costs nothing except maybe another rung of logic. If you use an S:4 bit, you can do it with the same timer you have already.

Try it, you will like it.

PS: The English word for a hand operation is "MANUAL", not "MANUEL". Because you are looking for INSITE instead of INSIGHT, it probably will not make any difference! I suggest checking your words with a spell-checker program of some type before putting them in the final PLC program.