Just Verifying

I am new to PLC programming. Its a tad hard for me to get my head around old programming habits. Would you take a look at the attached pdf and let me know what ya think. This is my first Logic Ladder

Welcome to the fourm
Couple of things...

What type of plc is it? Unitronics?

In rung 2 and 3 you have duplicated your AND logic...in rung two out 2 and out 2...once is enough same with rung 3

Can you say a little about what you are doing, you may get more comments

EDIT:
One other thing not sure about the PCL you are using but some the symbols are a bit different you may want to check..

( ) <--this being a output coil 

| | <--this being a contact you would still address it output 1 but it is shown as a contact not a coil

Your right its a Unitronics Jazz OPLC. Cheap little thing. Well ok hate to sound ignorant but like i said i am new to this. Here is what the Ladder does. It controls 2 air cylinders. The first cylinder is contected to a pump that needs to do 3 full cycles. (Bimba cylinders with magnetic reed switches so I know when the for and back strokes are done.) After 3 full cycles the other cylinder needs to run 1 full cycle and the Program starts over after the number of System cycles the user entered are complete.

On to repeat of logic. I kinda understand that but the program will still work right???

On to repeat of logic. I kinda understand that but the program will still work right???

Click to expand...

Yes, but keep in mind that you or someone else will look at your program...it may not be today or some day soon, but you want that person to have the best 'clear' chance to read and modify your program, I will look more tomorrow or maybe someone will else look tonight and reply, you ask will it work?...the good thing about a plc is if it does not work...then you just change it and make it work

I don not think it will work as is. In both Rungs 2 and 3, you have an Output repeated twice in series. I cannot understand the purpose of this. As Genius said, normally each output coil ( ) should be used only once in the program, but contacts || from any output can be used as many times as needed.

I think that the PumpMan in Rung 2 and the BoxMan in rung 3 really represents a switch input and should be a parallel "manual run" branch, not in series with the other reed switches. Unless the entire logic is for a manual step, in which case the first occurance of PumpMan and BoxMan should be input switch contacts || instead of output coils ( ).

Ok the output that is repeated twice is the cylinder manifold. Once for out once for in. Is that the correct way to perform that function???


Think I understand now. I have updated the Ladder. Is this better?

I have no idea how that PLC works but...I would say that this logic will not, give us a better idea of what you are trying to do...

In this rung why have both?


In this rung...can the box be open and close at the same time? if not this will not work, also a set and a reset in the same line will not work, tell us what you are trying to do, also is this the whole program? you may want to post the whole thing, how are you setting your bits?


Talk yourself through the logic, in and logic....you need this and that, this is what you have

In or logic you need this or that

Ok as per PumpMan and BoxMan. These are the manifolds I am assuming you have to set it (send voltage or amperage) reset it (cut off volts/amps)to have it extend. Then repeat the process to have it retract. I2 and I3 are correct those are the magnetic reed switches on the cylinders. So am i completely off and need to Just have [I2]-(s)-[I3]-(r)??????

I think you need to get a better understanding of the PLC scan. Understand that your rungs of code will be executed over and over again several (hundred) times per second.

To accomplish a sequence of events, you need logic that will change states of some address(es) during this logic scanning process.

If you have a basic understanding of hardwired relay logic, think in those terms to help you "wrap you head around" the concept.

The PLC will attmept to evaluate the outputs on each rung as though there were "electricity" flowing through the program at all times. Since a computer can only do one thing at a time, the "PLC ladder logic scan" is it's best attempt at emulating the flow of electricity in multiple parallel circuits.

Typically the CPU will update it's inputs, solve the entire program, updates it's outputs and repeat. This process will continue as fast as the CPU is capable of performing it as long as it is in run mode.

Hope this helps...PEC

Evocube said:

I am new to PLC programming. Its a tad hard for me to get my head around old programming habits. ...

Click to expand...

I think this is the issue, what programming have you done in the past?

Each rung for the most part is going to have one action.

I agree with Paul...

Try reading this it may help you understand the scan, PLC programming is not like writing 'C' or VB, but I think you can get it...

http://www.plctalk.net/qanda/showthread.php?t=14564

OK finally figured out my outputs are suppose to be [] not (). Put still cant figure out why my manifolds dont cycle. Thanks for the link that did help. I actually read it over before I posted.

This is more the logic you are trying to make


this is using a different PLC, but the structure should be some what the same

Make a discreption of what you are trying to do...make a list of steps, then we can help

1 if input 1 and input 2 then start pump
2 if not input 1 then reset bit 02...

thats the best way

Ok here is my explanation:
If input 0 run output 0, If input 1 run output 0 (repeat this 3 times then jump to net 2)
Net 2:
If input 2 run output 1, if input 3 run output 1 (do this 1 time return to net 1)

Ok Now I see I could remove input 1 and 3 with their outputs sequance <edit> but the reason I see this necessary is to retract the cyclinder (they are 2 way cylinders). My only problem is that I have tried several different things today with the system hooked up. Number One I cant get the manifolds to switch (Parker moduflex "S" series) I believe the PLC provides the power for this?? Number 2 is there a "standard starting sequance" aka startup bit??? I am really glad for this help and am trying not to be a complete idiot.

Well, in most plc's... The conditions you just stated need to be SEPARATED. They won't work if you do them all on one line. Do you have an online link to the Unitronics manual? I(well, I mean WE) will dig through it a little bit to see exactly what's allowed and what's not.

Now... Question for you...

Ok the output that is repeated twice is the cylinder manifold. Once for out once for in. Is that the correct way to perform that function???

Click to expand...

Some solenoids will work this way... Others will be extended when the output is ON, and retracted when the output is OFF. Others will require separate outputs... One output for extend, and one for retract. You'll have to double check which type your solenoid is, and get back to us.