New here - 2 Pumps 1 run 1 BU

Hi there,

Im Tom from Melbourne in Australia. Just getting started in PLC's. Im glad I found this forum.

My first little project is this one.

I have a situation where I need two pumps. One needs to be running all the time.(Picked with a selector switch)
If the Thermal overload (TOL) or Circuit breaker (CB) Trips, the other pump kicks in and then a fault light etc will come on until to tell the operator that an automatic switch has been made.


The part I am having trouble with is making the other pump come on as soon as the other has tripped.

Now I know this seems really basic. But I need to start somewhere.

Hope the information I have provided is enough for a start.

Thanks

Welcome to the forum, Tom!

Please forgive me if this is a real world application, but it sounds like a homework problem. Plenty of folks here will be glad to offer support & guidance, but few if any will take time out of their workday to solve the problem for others and rob them of experience.

If you can show us what you've worked on so far, we'll be more likely to help you work through any stumbling blocks.

Hello,

No, But fair call, Its not a homework problem. This is actually a situation in real life.
Well I guess it could be unofficially "Homework" as i'm just starting out and only have limited experience.

Ill post up what I have so far...

Cheers

Look at your problem this way.
I know you are starting out, so I may get over your head.

1. what components do you have to control the pumps?
2. what contacts are on the motor starters to tell you the motor starters are running?
3. what sensors do you have to tell you the thermal overloads have tripped?

Draw a sketch of your application using only 1 motor and then think the process through. Then add the second motor. Finally, what modification must be made to tie the two together using the plc.


regards,
james

one or two?

both units running from same plc?

Alright,

Firstly IS there any good tools for knocking up ladder logic on my Mac?
Im on the paper and pen still.

This is what I have.

Pretty much the top bit is actually wiring.

So the selector picks PU 1 or 2 to lead. If that pump trips out the fault coil (M0.0 , M0.1) in the PLC will bypass the selector and start the other.

Thats the basics of it down.

I decided to use only one fault light to save outputs.

IS this how you would approach something similar.

Ive thought about how I can tell if the pump is actually running, Does anyone know if someone makes a CT that has a NO contact that ill be able to feed into the Inputs.

Thanks

Nice start.

But you skipped step 1 of my other post. What are your electrical components?
Lets take a look at what you should have.

1 emergency stop
1 power on pb
1 MCR relay
1 power on light
2 start pushbuttons
2 stop pushbuttons
1 selector switch with 2 sets of contacts for pump selection.
2 green pump running lights
2 amber pump fault lights
2 motor starter contactors
2 pumps

By thermal overload, I take it to mean the overloads on the motor starter (contactor). If so, you should have 2 auxiliary contacts to tell you when the motor starter is energized.

I would create your electrical schematics and then look at the I/o.
note that many of these devices can be directly wired to the plc, but you first have to look at creating the electrical schematics.

Others may disagree, but that's the way I look at a project.
1. read and understand the specs.
2. write down the devices, horsepower, voltages
3. make a rough sketch or put devices in a spreadsheet.
4. write down a rough sequence of events.
5. expand the sequence to include the devices (don't worry about the I/o yet)
6. repeat step 6 several times to make sure you get all the devices.
7. write the sequence again and include the I/o points to define your I/o. At this point, you are the plc. what inputs turn on a device, what tells you to start, stop, turn off an output.
8. write the code in the order you wrote it down. DOCUMENTATION !!!!! is key.

REMEMBER !!!
keep the program simple to where maintenance can debug the machine.
work with maintenance, learn what they know, ask what they are used to, what plc's they have.

if they can't debug the machine, it's junk. production don't run because they can't debug the machine, management will hear about it, your company will hear about it, your boss will hear about it, and guess who is next and who gets to rewrite the program until the customer is happy??

Harsh words to hear perhaps, but this is reality. Build a good relationship with maintenance and your customers and you will almost never go wrong.

regards,
james

Thanks James,

Sorry If i was bit light on details.

Half in my head half on paper, Which is no help to this forum.

I'm an Industrial sparky by trade so I do have a fair understanding of circuits and other Industrial electrical equipment.

Your steps are quite helpful for me to work off tho. I hope you don't mind me using them.

Over the next few days ill create some proper drawings.
Still on the hunt for an easy to use program. Suggestions welcome.

From there ill return with a much better presented mock up.

Tom

No problem with using my suggestions.
I meet all sorts of individuals at work and you can't tell who knows what.
So I start at the ground floor.
Since you already know the electrical patr of it, prints shouldn't be that difficult.

I helped teach a class at a local university and the students didn't care about the prints, they wanted to write the program.
i started with the specs of an actual project and explained them.
i then did it step by step and as i explained things, they soon realized they didn't have things thought out.

I would suggest that you find out what brand of plc is at your facility. If you learn the one at your plant, you will be a valuable asset when a machine goes
down.

regards,
james

Shark93 said:

Still on the hunt for an easy to use program. Suggestions welcome.

From there ill return with a much better presented mock up.

Tom

Click to expand...

http://www.plcsimulator.net/

James Mcquade said:

I helped teach a class at a local university and the students didn't care about the prints, they wanted to write the program.
i started with the specs of an actual project and explained them.
i then did it step by step and as i explained things, they soon realized they didn't have things thought out.

Click to expand...

Kudos, James for your well thought out explanation. Great advice!

Shark93 said:

Ive thought about how I can tell if the pump is actually running, Does anyone know if someone makes a CT that has a NO contact that ill be able to feed into the Inputs.

Click to expand...

Tom,
In most every system I've been involved with, a N.O. auxiliary contact on the motor starter has been used for motor running feedback. Under special circumstances, I've used a phase monitor from Time Mark for proof of motor running.

Looks like you're starting off on the right track. Don't be afraid to post questions & ask for clarification on this forum. That's how we all learn. Become friends with the forum search tool as it has helped me on numerous occasions.

For motor running feedback, I like to use a current switch on 1 leg of the motor feed. That is the closest I can come to actually looking at the motor.