Pump Run time

[learner]

Hi,

Looking for simple logic or a Hint on how to constantly sort (promote) 4 pumps based on their run hours. The one with the least hours would be the First and so on to start.

Then on shutdown, the one with the most run hours would be the first to shutdown. Logic would be appreciated but even a hint is good enough.

Regards,

learner

 

[learner]

I guess I had way too many mistakes in my post. Sorry, it is RUN HOUR.

 

[Bit_Bucket_07]

This sounds like a homework assignment.
The first thing you'd need to do is to log the run time for all 4 motors.
Then you could perform a sequence of > or < comparisons and maybe latch or unlatch some bits that would allow you to detect which two pumps have the greatest and least amounts of run time.

 

[learner]

First of all thanks for taking time to respond. I was hoping for something that sounds a bit more creative. Second, this is not a homework / assignment. Done with homework for years. I don't even know what a person gain by saying such things like that on a professional forum?

Thanks again,

Learner

 

[jrwb4gbm]

See this old thread for some ideas.
http://www.plctalk.net/qanda/showthread.php?t=49120&highlight=hour+meter

See this pdf mentioned in a link within that thread.
http://www.plctalk.net/qanda/attachment.php?attachmentid=7006&d=1186257499

Don't be offended, your request does sound like a student homework assignment.

 

[rguimond]

I'm not sure what your application is, but I've always considered the logic behind hour-to-hour load sharing as flawed. Assuming the pumps were commissioned at the same time, they're the same model and have the same specifications, would it not be logical to assume they will start to fail at the same time?

To answer your question, I would set up a priority ranking (1-4) for each pump. After a fixed operating time, compare the hours each has run and sort their ranking accordingly. You could have the pump with the most hours move immediately to the bottom of the list, or move it back only one position per comparison. There's no right or wrong way to do something like this, so long as the end result suits the customer.

If the pumps are turned on in sequence and can be expected to have approximately the same duty cycle every time they're used, you could also set up a four-step sequencer so that every pump gets a different priority each day.

 

[Bit_Bucket_07]

First of all thanks for taking time to respond. I was hoping for something that sounds a bit more creative. Second, this is not a homework / assignment. Done with homework for years. I don't even know what a person gain by saying such things like that on a professional forum?

Thanks again,

Learner

Sorry about the misunderstanding. This forum often has students post here seeking help with class assignments. There are certainly more elegant solutions to your problem than writing multiple compare functions and latch/unlatch bits.

You don't specify which equipment you are using, but you probably have access to a Sort function. All that you need to know is which pump has the greatest and least amount of logged run time in order to execute your startup and shutdown logic according to specification.

 

[Bit_Bucket_07]

I'm not sure what your application is, but I've always considered the logic behind hour-to-hour load sharing as flawed. Assuming the pumps were commissioned at the same time, they're the same model and have the same specifications, would it not be logical to assume they will start to fail at the same time?

It might be logical to assume that, but it wouldn't be rational. In the real world, one (or more) of the new pumps might well succumb to an early death.

 

[learner]

No worries. Thanks for your help. I should've explain the question more clearly. Thanks again for your help.

Always a Learner. .

 

[rguimond]

It might be logical to assume that, but it wouldn't be rational. In the real world, one (or more) of the new pumps might well succumb to an early death.

That's possible! It's also possible they'll all succomb to an early death at around the same age. It's tough to beat vibration analysis for pumping applications.

 

[Bit_Bucket_07]

That's possible! It's also possible they'll all succomb to an early death at around the same age. It's tough to beat vibration analysis for pumping applications.

Agreed. It might well make more sense to install vibration sensors and order pump run time based upon vibration, rather than runtime.

 

[Tom Jenkins]

The popularity of equalizing run time indicates that at the very least it does no harm. The probability of "identical" pumps failing simultaneously is undoubtedly less than the certainty of a pump that is never run failing from bearing flat spotting, stuffing box failure, corrosion, etc.

I usually set an equipment number (1,2,3,4) and a priority (Lead =1, 1st lag = 2, etc.) to each. Then you can either cycle the priority every time the lead shuts down (alternation) or use comparisons to make the lead the one with the least hours.

Having said that, most of my applications didn't include automatic alternation. Most operators really could be counted on to periodically alternate - usually once a week. Automatic alternation also caused problems when one piece of equipment was out of service, when a repaired unit needed testing, and so on. I and most operators felt it was more trouble than it was worth. It is significant that the biggest advocates of automatic alternation are engineers, most of whom have never actually run a plant and some of whom wouldn't know a pump if it was shoved up .......

 

[Bit_Bucket_07]

Heh!

+1, Tom!