Staggered Start pumps

Dear All
I am using AB SLC-500 PLC
I like to write a PLC code to starts the 10 pumps in a sequencial order. These pumps will be ran by automatic sequence but i want to add a delay before they set output contact.
Many Thanks
salih

You could just use on delay timers. Start with the first pump delay then use that set output (or a signal telling you the pump has started) to start the delay time of the next pump . When a pump comes on it could start the on delay of the next pump. You can control the delays either by writing a preset directly in the ladder or by inputing data through an HMI. There are other ways to do this but this way is pretty simple.

I have done this by using one timer and one counter.
Example: Timer continiously resets itself every 45 sec. when it
resets it also increments a up-counter. I then use a compare
instruction, when counter eguals one start pump one. Next time timer
resets counter increments to 2. When counter eguals 2 start pump 2
and so on. You can also use a second counter to stop pumps.

Very efficient. I like it.

Or you can use one timer, set long enough for the whole "startup" sequence. In each pump's rung use a GEQ or equivalent type instruction to start each proceeding pump when the timer's acc. value is greater than the previous pump. For example, when the timer is GEQ 2 seconds, start pump 1; GEQ than 6 seconds, start pump 2, etc. You may have conditions that prevent you from using this method, but it is an alternative.

I just looked at my post again "EQUAL".

Salih,

You obviously haven't considered your "automatic sequence" very well.

I'll take a wild guess... after starting the first pump, your "automatic sequence" simply looks to "see" if the previous motor in the sequence is ON before starting the next pump.

The result of that type of sequence is that all 10 pumps start, or rather, try to start within a second or so. That is, even if you are waiting to "see" the "AUX" contact of a previous pump come ON before you try to start the next pump, all of the pumps start in sequence, very quickly, until the Main drops out.

If this is the case, then your "so-called" automatic sequence is inadequate. The design of the sequence needs to provide the delay.

I can't remember the AB style sequencer, but in TI, there are two types of sequencers. One is Event Only and the other is Event/Timer.

The Event Only type simply looks for signals. If you are using a sequencer, this sounds like the one you are trying to use.

The Event/Timer type looks for signals and then applies programmed delays before moving to the next step in the sequence. That is, Step-2 in the sequencer looks for Pump-1 being ON and then the sequencer applies the delay, programmed for Step-2, before moving onto Step-3.

If AB does not provide this type of sequencer (I wouldn't be surprised) then you need to run your "AUX" signals through an ON-Delay Timer. Then, in your sequencer, monitor the output of the ON-Delay Timer instead of the "AUX" contact itself.

If you are not using a "sequencer" then your "automatic sequence" needs to include a timer for each of the "AUX" contacts (except for, maybe, the last one... depends).

In any case, you should not start your pumps using a simple timer/counter combination nor an elapsed time scheme.

Any time you attempt to start a pump, if the pump does not start within a particular short period of time then your program needs to provide a Fault Indication.

Simply using a timer/counter combination, or an expired time scheme is "minimalist thinking". There are too many things that can go wrong.

I can not think of one situation where those methods are reasonable or adequate (unless, of course, you have complete faith and "KNOW" that the system will respond as you require... even if that damned #3-Pump is on fire!)

BTW, Mickey,
Since your timer had to have some start-value anyway, Rube was suggesting using a timer start-value that covered the entire start-up process - without the additional complication of a counter.

In many situations (not this one) that is an excellent solution to a time-sensitive sequence. The primary benefit is that each time-out situation can be individually tuned. That is, you can vary the sequence by varying the timeout values! That is BIG JU-JU!

If the individual pumps have the appropriate safety interlocks already built into their starting code, this shouldn't be hard.

In addition to the usual 'Power on, overloads not tripped, etc.' interlocks, add an interlock so that you can only start one pump at a time. I use a timer on each pump starting rung. The timing bits of each timer I want to interlock go to a common 'ok to start pump in system X' bit, which is a single rung located in a subroutine that is called before each start rung. Set the timers based on how long it takes the pump to start and what effect a pump start has on the system. I have to do it this way because most of my pumps are 200hp+ and starting 2 at once will likely trip the MCC breaker. Not to mention the effect on the system of starting 2 20,000gpm pumps at the same time...

In applications where automatic sequencing is required, tell the PLC how many pumps to run (or whatever condition you need to meet, i.e. minimum pressure or flow), then have it start pumps until it meets it or finds that it cannot meet it. The aforementioned interlock will do the rest. There will, of course, need to be some conditions put in to stop the startup sequence if something goes wrong. These will depend on your application.

I think this has been covered before

Furnace startup thread

Before I give my 2 cents I would like to know what kind of starters/contactors you using. Y-D, Accross the Line, or some type of soft starter with a "up to speed" output, etc..

Also you need to take inconsideration as to what you want to do if one or more of your motors or starters is faulted out.

Do you want to very the sequience? Are they transfer pumps or hydraulic pumps, (do they start under a load)?

What I'm trying to show here is that this is a very opened ended question......

Mike.

Salih

Are these pumps all in the same line or are they in different lines and you just want to sequence them on to prevent loading your control panel up by turning them on at the same time?

If your pumps are in the same line, you will need to be able to tell that each pump has come on before the next, (in which Terry is correct- the single timer sequencing will not perform well). You will need something other than aux contacts from the drive/contactor to tell the next pump to come on; you will need a pressure transducer (or maybe a flow transducer). Simply coming off of the drive's aux contacts tells you the pump was told to come on but it doesn't tell you that it actually did.

If you are simply preventing high surges across your fuses or circuit breakers, I respectfully disagree that a single timer is too "minimalist". We start conveyors (and I have started pumps in different lines) all the time with a single timer and not only does it work well, it's easy to program. You must, as Waterboy points out, make sure all necessary safeties are in place--with either scenario.

Sequential Start

They are all across the line starters. I can handle the time delay start up. But the stop in the right order is giving me a little headache. Do any of you guys have a file on some of your work that I might be able to see.

Re: Sequential Start

elitheei said:

They are all across the line starters. I can handle the time delay start up. But the stop in the right order is giving me a little headache. Do any of you guys have a file on some of your work that I might be able to see.

Click to expand...

elitheei,

Why dont you post your code, and then maybe somebody can help you with it?

Regards, Mike.

How about a shift register and a timed pulse. The bits from the shift register will determine the order and you would only have to use those bits in a simple set/reset fashion or latch/unlatch.