Oil pump and motor question

pkb2050

Member
Join Date
Sep 2009
Location
India
Posts
27
I have just stated learning ladder logic and here is a question which is worrying me a lot.

Q:- An oil pump should start up after pressing start push button and the main motor will start automatically after 15 sec. After pressing stop push button main motor will stop immediately and the oil pump will stop automatically after 15 sec. make a ladder logic
 
Even though this may seem straightforward, draw out a timing diagram. It will help keep your thougths clear.

You probably have the first part done, the part with delaying the motor start. For this you most likely used an on delay timer (TON), since you wanted to delay turning on the motor. On the other end you want to delay turning something off. So, logically, you would want a ... what type of delay? AB PLCs, and most other plcs, have an instruction for just such a case.

Keith
 
do you need any other stuff? like a pressure safety low on the pump? how about affirmation that the motor is actually running?
 
I have just stated learning ladder logic and here is a question which is worrying me a lot.

Q:- An oil pump should start up after pressing start push button and the main motor will start automatically after 15 sec. After pressing stop push button main motor will stop immediately and the oil pump will stop automatically after 15 sec. make a ladder logic

OK you are a student. Students are there to learn because they do not know it. Students have homework which is overwhelming at the start. You have a choice either worry it to death or get started on the solution.

NOTE we will not do your homework for you. We could give you the whole program to give you a top grade and it would only take us 15 minute. After some practice and mistakes you will be able to do this in 15 minute also.

Your assignment clearly states what needs to be done.

Next step is to make a sequence in writing of what needs to happen ie 1 2 3 etc.
ie
STEP 1 push start switch
2. Oil pump start
3 time delay
etc etc
When you have the sequence all written out then you can start assigning switches time delays to it.

Answering comment about pressure switches to confirm oil pressure
yes in real world that would be needed. Stay within scope of assignment and get that done then you can add oil pressure switch later.
Dan Bentler
 
OK you are a student. Students are there to learn because they do not know it. Students have homework which is overwhelming at the start. You have a choice either worry it to death or get started on the solution.

NOTE we will not do your homework for you. We could give you the whole program to give you a top grade and it would only take us 15 minute. After some practice and mistakes you will be able to do this in 15 minute also.

Your assignment clearly states what needs to be done.

Next step is to make a sequence in writing of what needs to happen ie 1 2 3 etc.
ie
STEP 1 push start switch
2. Oil pump start
3 time delay
etc etc
When you have the sequence all written out then you can start assigning switches time delays to it.

Answering comment about pressure switches to confirm oil pressure
yes in real world that would be needed. Stay within scope of assignment and get that done then you can add oil pressure switch later.
Dan Bentler
I want to tell you sir that i am not a student and not given any such homework its just for my hobby.
 
Studying and trying to learn PLC at home is even tougher than being in a class. I know I tried. When I had a PLC with just the power leads hooked and nothing else and had an energized output. I had no idea why and decided that this was dangerous and I had no comprehension of what I was doing. I unplugged it sat back and thought about it and concluded I had a completely unqualified instructor. So I went and found a qualified instructor at a local community college.

What you are trying to do is admirable. Tell us more about what PLC you are using and what applications you have in mind for it.


Dan bentler
 
It might also help you to think of it in steps, almost like a flow chart. Each Step has an action associated with it. To get from one step to the next step requires some condition to occur. For your example:

Step 0 (idle) - Do nothing

Step 0 to Step 1 Condition - Start PB

Step 1 - run oiler, run timer

Step 1 to Step 2 Condition - Timer Expires

Step 2 - run oiler and main motor

Step 2 to Step 3 Condition - Stop PB

Step 3 - run oiler, run timer

Step 3 to Step 0 Condition Timer Expires

You might also consider what happens if the Stop PB is hit while in Step 1.

If you think of each step as a bit, then the logic becomes fairly simple. IE, run oiler when I'm in Step 1, 2 or 3. Run Main when in step 2. Run On Timer when in Step 1. Run off Timer when in Step 3.

Likewise, the conditions are just bits too. Timer Done or Start Input, or Stop Input.
 

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