2 Alternating pressure pumps Lag/Lead/Standby

1010101 · Dec 5, 2014

I need to create a system of 2 alternating pumps in ladder logic. I am using RSLogix 5000
2 pumps controlled in 3 modes (OFF, Manual and Auto).
OFF=Out of service
Manual=Stop (NC), Start (NO), Reset either pump.
Auto= Stop(NC), Start(NO), Reset - One pump starts and the other is on standby, the pump that is started first in auto will make the other its standby

I want to make it so that if the main pump is running and drops below 25% pressure the opposite pump will start automatically and the original pump will shut down and the reset light/switch will activate. Both pumps can never run at the same time

I searched the forums and saw a couple threads that seem like they might give me a good start but most of the programs are using micro 1000 like this thread.
http://www.plctalk.net/qanda/showthread.php?t=9499&page=3

Still a super novice at PLCs

1010101 · Dec 7, 2014

Hey guys this is what I have come up with so far using a couple threads I searched off this forum. I modified another program from 3 to 2 pumps, but I need to incorporate a pressure switch that controls which motor runs.

Start a pump auto or choose which is stand by then if the pump falls below 25% pressure pump 2 turns on and pump 1 turns off.

Can someone tell me how I would do this?
Sorry for the cured mspaint drawings. The RSlogix5000 demo is not available anymore and I didn't have access to the program.

Bering C Sparky · Dec 7, 2014

I dont think your attachment made it onto your post.
Try again.

1010101 · Dec 7, 2014

are the pictures not showing?

Bering C Sparky · Dec 7, 2014

1010101 said:
are the pictures not showing?

You see the same thing everyone else does.
They might be there?? I dont have on my glasses at the moment.

1010101 · Dec 7, 2014

Bering C Sparky said:
You see the same thing everyone else does.
They might be there?? I dont have on my glasses at the moment.

lol yeah I see the pictures. I was just wondering because they are pretty big and hard to miss.

1010101 · Dec 7, 2014

I'm thinking I can use the CPT instructions to scale. I am confused on how to implement my idea. There is no specific tank size or shape.

I want to calculate the current pressure of the activate pump (thinking CPT) then if it is LEQ to 25% alternate which pump is on and which is off.

I don't now how to trigger my one-shot relay that controls which pump is running using a pressure transmitter.

Bering C Sparky · Dec 8, 2014

Oh, you do have pictures, they were not showing up on my work computer for some reason, thats weird.
On my personal laptop now and see them fine.

Anyway a couple of questions for you.

1) Is this a project for school?

2) Are you using a pressure switch that has a simple make/break contact that would be used with a digital input, or are you using a pressure transducer where you can input full range pressure via a analog input?

3) Kind of confused about your switch configuration, You have Off, Manual (Hand) and Auto. But then you also say "Stop N/C & Start N/O???? Is there also a start stop push button station somewhere??

If pump is in manual do you want it to run all the time no matter what until you take it out of manual? (this is usually the case with manual) or do you want it to shut off at < 25% flow and switch to the other pump if the other pump is in auto?

Or do both pumps need to be in auto for the transfer from one pump to the next to take place? (this is more typical)

What do you want to happen if one pump is in auto and then you turn the other to manual? (does the pump in auto shut off and the manual pump run?)

If one pump is in auto and the other is turned off but the pressure drops off to <25% do you still want the auto pump to stop and have no pumps running?

Sorry for all the questions but understanding the entire process is always the first step before you start to program anything.

If you don't have software take a look at the link below.
It is not Logix5000, its Logix500 starter, but its better than programing with PAINT and you can download the emulator also and test run your logic.

http://www.rockwellautomation.com/rockwellautomation/support/plc/micrologix.page

Will you actually have Logix5000 to run this program on once you finish it?

BCS

1010101 · Dec 8, 2014

Bering C Sparky said:
Oh, you do have pictures, they were not showing up on my work computer for some reason, thats weird.
On my personal laptop now and see them fine.

Anyway a couple of questions for you.

1) Is this a project for school?

2) Are you using a pressure switch that has a simple make/break contact that would be used with a digital input, or are you using a pressure transducer where you can input full range pressure via a analog input?

3) Kind of confused about your switch configuration, You have Off, Manual (Hand) and Auto. But then you also say "Stop N/C & Start N/O???? Is there also a start stop push button station somewhere??

If pump is in manual do you want it to run all the time no matter what until you take it out of manual? (this is usually the case with manual) or do you want it to shut off at < 25% flow and switch to the other pump if the other pump is in auto?

Or do both pumps need to be in auto for the transfer from one pump to the next to take place? (this is more typical)

What do you want to happen if one pump is in auto and then you turn the other to manual? (does the pump in auto shut off and the manual pump run?)

If one pump is in auto and the other is turned off but the pressure drops off to <25% do you still want the auto pump to stop and have no pumps running?

Sorry for all the questions but understanding the entire process is always the first step before you start to program anything.

If you don't have software take a look at the link below.
It is not Logix5000, its Logix500 starter, but its better than programing with PAINT and you can download the emulator also and test run your logic.

http://www.rockwellautomation.com/rockwellautomation/support/plc/micrologix.page

Will you actually have Logix5000 to run this program on once you finish it?

BCS

1)Yes, this is one of my labs for class. Intro PLC course and I do have logix 5000 to run and logix5000 to emulate this program.

2) There will never be a "real" pressure switch as this program will never actually be used other then being emulated. I'm looking for the easiest solution here.

3) Yes, I want to incorporate a stop, start and reset button for each pump. Stop and start will be used to change which pump is lead. Off just means the pump will be the lag pump and turn on if the other pump drops below 25% pressure. If both pumps are off nothing happens. Both manual, which ever the operator makes standby is the lag pump. Both auto, pump 1 is lead.

4) Pump 1 is the main pump. At any time if the pressure were to drop below 25% pump 2 would start automatically and pump 1 would shut-down. I want to put a reset push button and light here.

If one pump is in auto and the other is put to manual then the auto pump is the lead pump and the other will only turn on if the auto pump drops below 25% pressure.

The pumps can never be run at the same time. If both are set to auto, pump 1 is lead. If one is set to auto/manual and the other is off then the auto/manual pump is lead and the "off" pump will still kick on if the lead pump drops below 25%.

I know the way I worded the OP is confusing and I do not mind the questions, I'm here to learn.

1010101 · Dec 8, 2014

Bering C Sparky said:
http://www.rockwellautomation.com/rockwellautomation/support/plc/micrologix.page

Will you actually have Logix5000 to run this program on once you finish it?

BCS

This is a HUGE help. I didn't know rockwell offered any other demo/starter programs. I know there used to be a RSlogix 5000 demo, but it was taken down from their site. Not being able to test my logic has been the biggest handicap in this course. There is only so much you can learn in a 3 hour time span 2x per week. There are only 9 computers with this program and we are able to remote access from anywhere on campus. 90% of the time you're lucky to get access outside of your lab time and even then people are able to kick you if they try to remote access into the same comp.

Bering C Sparky · Dec 8, 2014

Well, ok then I guess.
That is a very odd switch configuration though, unlike anything I have ever seen or heard of.

But I suppose as long as it is not going to actually be used then anything is possible.

So then if pump #1 is in auto and the pressure drops below 25% then pump #2 will come on if it is set to Off, Man or Auto. (Not something you would see in the field.)

Do you have what you have done so far saved in .ACD file that you could attach to this site that we could look at? In one post you say you don't have access to the program but then you say you do. ( I am guessing software is at school )
If you do have it post what you have so far to the forum.

If you don't have the software.
Try to download the Logix500 starter I linked you to.
It is different than 5000 but the ladder logic is basically the same.
That way you have some format to work on at home, and a way to post your work to the forum so others can help guide you.

BCS

Lancie1 · Dec 8, 2014

This old post had a very similar 3-pump alternation. My program in Post #8 seemed to solve the problem. Add a pressure switch contact to Rung 6. The pressure contact can be controlled by a analog input, or you could use a comparison (Less Than) instruction in place of a pressure contact. You will have to convert the logic to RSLogix 5000.

http://www.plctalk.net/qanda/showthread.php?t=82543

EDIT: I see now that your problem is different. It only has 2 pumps with a Off-Manual-Auto selector switch. That is different but also easier. All you need to do is set up a common 3-position selector switch control, then add alternator or flip-flop logic that is activated in the Auto mode.

Lancie1 · Dec 8, 2014

If one is set to auto/manual and the other is off then the auto/manual pump is lead and the "off" pump will still kick on if the lead pump drops below 25%.

Are you certain this is correct? In the electrical control world, turning ON a pump (or any device) that has a OFF condition selected by a switch is a big "DO NOT EVER DO THIS"! Normally if a Pump is in Manual, then that also controls the Pump with a manually-operated switch. If the Auto mode is selected, only then should your pressure switch and the alternator take charge.

I will write you a version that would not violate any of the normal safety rules, but still alternate when the pressure drops. See if you think this may be the real intended problem.

Alternating Pumps w Pressure Switch- 1010101.JPG

1010101 · Dec 8, 2014

Lancie1 said:
Are you certain this is correct? In the electrical control world, turning ON a pump (or any device) that has a OFF condition selected by a switch is a big "DO NOT EVER DO THIS"! Normally if a Pump is in Manual, then that also controls the Pump with a manually-operated switch. If the Auto mode is selected, only then should your pressure switch and the alternator take charge.

I will write you a version that would not violate any of the normal safety rules, but still alternate when the pressure drops. See if you think this may be the real intended problem.

The logic for Auto, Manual and Off was my choice, but I see I made a big mistake there. Thank you for taking the time to write that program. Even though this program won't ever be used in a real time system I want to make sure I'm not violating any safety rules.

1010101 · Dec 8, 2014

Hey Lancie,

I have a question about the tags. RSLogix5000 Emulator controller is in slot 1, I'm using a 1756-IF8 in slot 2, 1756-IA16 card in slot 3 for my inputs and 1756-OA16 card in slot 4 for my outputs.

what is B3:0/0 referring to as far as tags for the first two rungs? I'm using RSLogix 5000 and I have Local:2:C
Local:2:I
Local:3:C
Local:3:I
Local:3:O

^ These tags expand. I used the input card data spots 1-6 for rung 2 and 3. Same for the outputs in those rungs, but I am not sure which tag to use for the source of the LES and the storage bit/output bit of the OSR (RSlogix5000 OSR looks slightly different)

2 Alternating pressure pumps Lag/Lead/Standby

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