Slc504

I have an SLC504 controlling 8 large refrigeration bays. I have them set up to defrost every 8 hours (of running in cooling mode) for 20 min.

What I want to do is limit it so that only 2 bays (any 2) can run a defrost cycle at one time. When either of those is done the next in line will begin it's defrost.

Any help is appreciated.

Thank you,
Shane

if you already got the 8 hour figured out. Then use that completed time (either counter or RTC) as a trigger to counter 1 set for 20 min.
turn on 2 pumps. then use counter 1 completed to trigger counter two for group 2. counter 2 completed to trigger counter 3 etc for your 4 groups. This should present no problem to quickly program in.

Thank you for your reply mordred.
I am sorry I failed to give you all the necessary info. oops.
These bays are not constantly cooling so they will not all defrost in a nice cycle as you were describing. (I wish that was the case)

So a user can turn the bays on and off when they need. If a bay has run in cool mode for 8 hours it goes into defrost and in a worse case senario they could all go into defrost at the same time. They use steam to heat so to avoid mass steam consumption at once I would like to limit this to 2 bays at a time.

Need more info...

Shane,

I have some questions about this operation. If you run a cooler for 5 hours and then shut it down for awhile, when it starts back up, does the counter start at 5 hours or does it reset?

How detrimental would it be if a cooler runs for 9 hours while waiting "in line" to be defrosted?

If you could attach your .rss program (if it's <300Kb)I could see what you're doing.

If you can't here is an idea for some of your problem:

Instead of triggering the defrost directly when a cooler reaches 8 hours, have the PLC set (OTL) a bit for each cooler that is a "Ready to defrost" bit.

Use this bit, conditioned with a counter, to trigger a "defrost" bit for that cooler. Monitor these "defrost" bits with the counter. If the counter is LEQ 2, the "defrost" bit for that cooler can be set. When this defrost bit is set, have it retained by the defrost timer timing (.tt) bit and have it OTU the defrost "ready" bit for that cooler.

I'm not sure exactly how to track which cooler to defrost next based on the first question I asked, but this should get you started.

It will not be detrimental to go past 8 hours on a cool.

Anyway I have attached my RSS file. I am in the middle of editing bay 3 but bays 4-10 are all identical.

Basically I have an RTO that times when ever the coolant solenoid valves are energized. Once that gets to 8hrs it will defrost for 20min. unless the cooling system is turned off for 10 min or longer.

I don't have a ton of programming experience so please give any advice that you think is helpful.

Thank you.

I gave it a shot...try this. This should defrost 2 bays at a time in the order in which they reached the 8 hour mark. It will leave the others waiting in line if there are more than 2.

I wrote the logic for a MicroLogix because I only have the free version of Logix at home, but you should be able to adapt it to a SLC very easily. Also, since I only have the free version, I could not see your file you posted, so I'm sure you will have to make adjustments.

I'm "fairly" sure this will work, but I have no way of testing it, so if anyone sees a problem with it or has any constructive criticism, please let me know. I'm always up for learning something!!

This might also work

Between this file and the FIFO code from shoelesscraig, you should be able to get some good results. His FIFO stuff works well to keep the bays in order for defrost.

Hope this helps

sfindley said:

Between this file and the FIFO code from shoelesscraig, you should be able to get some good results. His FIFO stuff works well to keep the bays in order for defrost.

Hope this helps

Click to expand...

Just so I can get an idea of how you did it, if you don't mind could you post your file in PDF form, or change the processor to a ML1000 or ML1100? I can't view SLC processors!! Thanks!

Here you go

Sorry for the abbreviated replies and incomplete code...having a busy night in the mill.

Thank you all very much for all your info so far. I have not been able to look too closely yet. I am having a busy night as well. Will look over soon.
Thanks again.