Exceeded Cycles/Starts per X amount time

I've been asked to provide an alarm for if a pump starts too frequently during a given time. The operator should be able to enter X starts per X time and if it happens it generates an alarm. What is the best way to do this? (I was successful in creating one with an hour timer for a test but it's not a true hour if you know what I mean.)


I did multiple searches and the closest scenario I found was this one but it's not helping me: http://www.plctalk.net/qanda/showthread.php?t=55470&highlight=hour+counter

Any reply would be greatly appreciated. Thanks.

(I am using a Micrologix 1400 and a CMore HMI. I am mostly interested in the ladder logic required to accomplish the task)

As always, there a number of ways to do this.

Please tell us what PLC you are using in your application, and what HMI you are using to Input the Data.

Stu....

Oh my bad, I'm using a Micro 1400 and a CMore. Thanks.

It's looking like I need more experience using FIFO instructions. Anyone have an example of what I am trying to do here by chance?

My suggestion is ....... don't do it!
The simplest solution is to have minimum run time and stop time timers to prevent the pump from cycling too often.
example: to limit the pump to 6 starts per hour set the total of the two timers to ten minutes.

I am not familiar with the CMore HMIs, but the way I would do it is with a one minute self resetting timer, two Counters, and and Enable Bit.

A Screen on the CMore will have entries for the Minutes, and number of Allowed Starts, and an Enable/Disable Button. When the Enable Button is activated, I would Enable the Timer, and the Two Counters. This is assuming the CMore can Write Directly to the Counter Presets, if not, then I would Write them to and Integer N Location, and I would Move (MOV) the Entered Numbers into the two Counter Presets when the Enable goes True.

One Counter is Incremented every Minute, the second Counter would Count every Pump Start. The Done Bit from the Minutes Counter would Reset the Pump Starts Counter, and the Done Bit from the Pump Starts Counter would Alarm, and shut down anything required.

If you require a sliding Time Window, that is going to get more complicated.


Stu....

Thanks Stu,

Yes, the CMore is capable of all those things. I'm mostly interested in the PLC logic required to accomplish the "Sliding Time Window" that you speak of. I couldn't think of a proper term for it but there it is..."Sliding Time Window". Perhaps now I can do a better search. I need to make a sliding time window for an exceeded pump cycle alarm.

First, do what mendosy said, and install timer logic to prevent short cycling and pump damage. The minimum off time and minimum run timers should not be compromised.

Then, just FIFO the timestamp when a start is issued.

Set the LENgth of the stack to the number entered for "X_Starts" on the HMI.

When DN, check the value at the DN position against current time by subtraction with rollover detection.

If that result is less than the HMI tag "Y_Time" seal or latch an alarm bit.

You FFL (Fifo load) when the start occurs, and the data you load goes into the current positiion of a stack.

When the stack is DN (full) you unload it, examine the contents, etc.

Make the stack bigger than you need, and use your own pointers to get the third in a list of say 256 start timestamps.

Put them in parallel if desired to get all six pieces of the clock in the timestamp.

Or, for more tidy storage, encode the time... like a float where time is DDHHMM.SS and you can go further if the clock allows millisecond precision.