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Old November 16th, 2012, 07:01 AM   #1
mayank_04081989
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Need help for drawing PLC ladder diagram

Hi,

I'm new to PLC ladder diagrams and I'm stuck in a problem where I'm given a ladder diagram (please refer to the attached file "Problem"). I need to have a PLC 5/30 control System. There are 8-point I/O cards with one-slot addressing.

It is required to draw the inputs and outputs which are attached with the post as "Inputs" and "Outputs" respectively. As per my understanding there are 4 inputs (stop-1, start-1, stop-2, start-2) and 5 outputs as shown in the attached file.

I tried to construct the PLC ladder diagram (please refer to the attached file "PLC_Ladder_Diagram").
In this diagram I could not include the float switch which energizes CR2. Also I did not understand how to include OL's in the PLC ladder diagram.

I tried to run a simulation of the PLC Ladder diagram though it is incomplete because I did not how to include the float switch. Attached file ("Problem1.plc"). Please help me to include the float switch in the PLC Ladder diagram.

Thanks in advance.
Appreciate your help.
Attached Images
File Type: jpg Problem.jpg (31.6 KB, 64 views)
File Type: jpg PLC_Ladder_Diagram.jpg (30.6 KB, 56 views)
File Type: jpg Inputs.jpg (21.1 KB, 44 views)
File Type: jpg Outputs.jpg (23.6 KB, 40 views)
Attached Files
File Type: plc Problem1.plc (2.3 KB, 42 views)
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Old November 16th, 2012, 07:18 AM   #2
raccjim
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looks like all rungs of your diagram south of rung 3 are controlled by CR1...assign your float switch to an input address, add a rung which depends on both the CR1 and Float switch instructions to be true to energize the output instruction controlling CR2. The overloads are included in the power diagram and are not necessary in your PLC logic...
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Old November 20th, 2012, 01:10 AM   #3
mayank_04081989
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Thank you.

Ok, so does that mean that there are five inputs and not four (if I consider the float switch as an input)? Should I change the diagram in the figure "Inputs" by including the float switch as an input?

Thanks for your help...
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Old November 20th, 2012, 07:14 AM   #4
raccjim
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Well, if I was writing the plc ladder myself, i would connect the float switch as an input, the other solution would be to connect the float switch as hardware between the PLC output to CR2 and the control relay coil.
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Old November 20th, 2012, 08:16 AM   #5
mayank_04081989
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Thanks a lot. This simplified the problem for me.
However, I am still struggling with the addressing. Could you please help me with addressing as well... There are 8-point I/O cards with one-slot addressing. All cards are in rack 0. The input cards are in slot 0 and output cards in slot 1. If it is a one slot addressing, how can there be slot 0 for inputs and slot 1 for output cards? I have read the rockwell manual for address as well but still struggling...
I have redesigned the diagram with addressing. Please find the attachment "solution".
Also coil relays are used as output as well as output. Is it correct to place the instance or CR1 (an output) as an input in the next rung?

Thanks in advance..
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Old November 20th, 2012, 09:05 AM   #6
raccjim
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Is there no processor in your rack? Are you using slc500, or 5K? Typically your processor would be in slot 0, then IO cards...So, for slc500 for example, if your input card is in slot 1, your addresses would be I:1/0-I:1/7(I=input,1 being the slot #, and 0 being the first point on your input module) for an 8 point card, output card in slot 2,addresses O:2/0-O:2/7...your CR1 output coil, which in your drawing I believe you addressed as O:001/00 can be used via examine if open(XIO) or examine if closed (XIC) instructions on subsequent rungs,as per your diagram your second rung would go false when CR1 was energized, etc.

Last edited by raccjim; November 20th, 2012 at 09:11 AM.
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Old November 20th, 2012, 10:46 AM   #7
raccjim
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Also, on your fifth rung, it looks like your seal-in instruction is mis-addressed, should be O:001/07
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Old November 20th, 2012, 11:39 AM   #8
raccjim
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Sorry didn't see the 5/30 mentioned in your original post, my experience is limited to 500 and 5k, maybe someone else can help you with the addressing
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Old November 21st, 2012, 12:18 AM   #9
mayank_04081989
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Thank you. Yes, the seal in instruction in the fifth rung is incorrectly addressed. I will correct it.
Thank you so much for your help
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