PLC Design Assigment Assistance Needed

[joe malcolm 0]

Hi everyone new to this, I've been working on a college assignment for instrumentation engineering and have been given a design task. I've been going through it but I don't really understand designing programs, in this case ladder logic. Any assistance would be brilliant and any additional general help on PLC Programming would be appreciated, as I really enjoy PLC topics but seem to struggle. Heres the problem given: There is an industrial oven on your site used for heating bearings for motors in the repair workshop and the bearings are heated up to a normal temperature of 80 degrees celcius.. Lately electricians in the repair shop have been asking for local indication of the process. 1) When the beaing is placed in the oven and a door switch is made as the oven door is closed the light should indicate amber for 5 seconds. 2) After the 5 seconds the oven automatically heats up and the red light comes on for 30 seconds indicating a bearing is being heated up. 3) After 30 seconds the oven is switched off and the bearing is allowed to cool inside the oven with an amber light on for 10 seconds. 4) This is replaced with a green light for a further 15 seconds and then the green light goes off meaning the bearing can be removed safely and retaining enough heat to place on to the motor shaft. 5) Try to incorporate any safety interlocking with the door switch and alarm conditions to enhance your program. Ive got as far as point 2, using a retentetive timer in step 1. As I said earlier any assistance would be appreciated and any explanations to help me better understand PLC's/Desing. Thanks in advance, JM

[Matt Seiman 0]

Post the PLC program that you have so far.

[joe malcolm 0]

Hi Matt thanks for the reply, I currently have this | | OPEN, |-| CLOSED X000 T250 --| |--------|-|---------------------------------(M1)--- M1 --| |--------------------------------------------(T250 K50)--- X000 --|-|--------------------------------------------[RST T250]---- M1 --| |-----------------------------------------(Y000)---- See I've just got the amber light (being y000) for 5 seconds but I may have written this out wrong. Thanks in advance, Joe

[Matt Seiman 0]

Are you using Allen Bradley software, Omron software, C-more....??????

[joe malcolm 0]

Hit Matt, Thanks for the reply. I'm using Mitsubishi GX Developer on various types of PLC in the lab at college.

[OkiePC 14]

This is a good structure to follow for a controlled sequence, you would have to translate it to Mitsubishi though, but that should not be too hard. The approach in the link takes a program written on paper as a block diagram with decisions and transitions between states in human readable form, and enforces it in ladder logic. http://www.plctalk.n...560&postcount=8 That example was quick and dirty, but the point is to keep the area of code controlling the sequence all together, run logic to use the overall mode and those state bits to drive the output logic afterward. You can design a fairly complex process very quickly with this method. You draw out the states on paper, and draw lines between them to identify the transition requirements, which become branches in the ladder code. Edited 28 Jan 2013 by OkiePC

[joe malcolm 0]

Thanks for your reply friend, I appreciate the help. However that seems very complex for me and I dont quite understand what you mean. My program is probably going to much simpler. If you could further explain the last bit about drawing the states out on paper? Sounds helpful but I dont quite comprehend what you mean, sorry! Kind regards, JM