Triplex or Lead Lag Lag 2 rotation

[829]

Hello everyone. I am trying to figure out what the best way to control three pumps would be. I have searched the forums and cannot seem to find what I am looking for, so I will be as detailed as I can. The two attached files are pdf and the test "works", but does not increment, which I believe some math would take care of. However, I am looking for a simpler(sp?) and more streamlined way of do this.

Issue: Control 3 pumps in rotation.
Rotation: Lead, Lag, Lag2.

Control Tank calls for pumps, based on level setpoints. Lead is called, if unable maintain, lag is called, and if still dropping lag 2 is called.

Once level is met for the respective set point, the pumps turn off and rotate.

I am using 3 counters to keep track of the pumps rotation status.

My current crappy code is rotating mostly working like I want. I am forcing a position change if one of the pumps becomes unavailable. However, when the pump becomes available again, I am looking back at my original counter, which is not set to increment, so the pumps go back to their original position. I do not like this method at all and I am just not smart enough to figure it out. My preference is to have the pumps rotate normally, but if a pump is removed from service, the system will operate in a lead, lag operation, but when the 3rd pump comes back into service, it will hop back into rotation. Caveat, I need to always have them rotate in a lead, lag, lag 2(if available) sequence. For example, the operation would be L, Lg, Lg2, rotate after lead call drop, L2, L, Lg and so on. Lets say pump 1 is down down for maintenance, the L and Lg would rotate between 2 and 3, but when pump 1 came back online, it would find its place in the correct order. There are other things in the code, which may be left over from trying a bunch of different ways to achieve what I want.

Pump 1 rotation counter: C5:3, using the acc
Pump 2 rotation counter: C5:4, using the acc
Pump 3 rotation counter: C5:4, using the acc

I am moving the acc of each counter to N10:40, 41, and 42 respectively.


I hope the above word salad is somewhat coherent, if not, please let me know. If anyone has any examples of what I am trying to accomplish or can point me to a good resource for this, please let me know.

Thank you

[829]

I forgot to mention that the PLC is a Micrologix 1400 and I am using RSLogix 500.

[ianingram]

Hi,


I have done the same project as this, with a Micrologix - see the attachment.

I based the motor selection based upon calculating the motor with the least amount of runtime. The motor with the least amount of runtime then becomes the lead motor. If a motor is unavailable(say in alarm) then it cannot be the lead motor.

Have a look at the attachment and let us know what you think

[cardosocea]

Just a small reminder that things fail and if the pumps are exactly the same and have the same exact number of hours on them, they'll likely fail fairly close to one another.

It obviously depends on the duty, process, maintenance regime and so on, but it's worth bearing that in mind particularly if they're to be used in a safety layer of sorts.

[drbitboy]

Bookkeeping. I rotated the other way (L,Lg,Lg2 => Lg,Lg2,L).

[829]

Thank you for the replies, I will be looking them over.

[g.mccormick]

i will try to remember to pdf and upload some code that i have for doing this. mine in in studio 5000, however the basic idea is the same. i chose to alternate every sunday and i have built into the logic ramping of the the starting pump and stopping pump too. my process runs basically 24/7.

i will try to remember this this weekend

[829]

Originally Posted by g.mccormick

i will try to remember to pdf and upload some code that i have for doing this. mine in in studio 5000, however the basic idea is the same. i chose to alternate every sunday and i have built into the logic ramping of the the starting pump and stopping pump too. my process runs basically 24/7.

i will try to remember this this weekend

Thank you

[TheWaterboy]

Rotate every Sunday.... I never even considered that option... What's the thinking there? Not that its wrong or anything, just wondering.

I have a unique twist in that many of my locations that have multiple duty pumps maintaining pressure and a single massive fire flow pump for .. well you can imagine.

So while I rotate through the others every call, I rotate that one at night (avoiding demand charges) once in every 50 cycles of the others just to keep it moving after finding that the bearing would be damaged from sitting too long. The floor vibrations would vibrate the balls into the races.

I wish they were on VFD's so I could just spin them slowly once in a while without spiking the system from the sudden pressure increase.