Boiler Lead/Lag system

Joe. B

Guest
J
I have recently set up an Automation Direct DL06-AR controller to alternate the operation of two boilers. I'm using the controllers analog capabilities to monitor steam pressure and turn on/off the boiler based on steam load. I currently use a counter to alternate the boilers based on a run time set via operator interface.
Example of current operation:
1.Steam pressure falls below 6 psi - boiler #1 starts
2.Delay Timer (Operator adjustable) 2 min.
3.If steam psi hasn't reached 8psi(operator adjustable) in 2 min.
boiler #2 starts.
4.Both outputs latch until psi reaches 11 (user adjustable)at which point both boiler outputs open until psi drops below 6.

My counter sequence is such that the outputs continue to alternate and I can't turn on one boiler and designate it as the lead. I would like to incorporate an hour meter for each boiler to monitor run time for maintenance purposes and to turn on/off chemical pumps.
I hope I explained this well enough. Suggestions would be greatly appreciated.
 
My counter sequence is such that the outputs continue to alternate

Sounds like your usng a compare statement without additional timing, it's doing exactly what you programmed it to do. When boiler 1 starts, it accumulates run time, and it then exceeds the run time of boiler 2, the Lead/Lag logic compare solves, and switches the boiler lead/lag sequence. Then boiler 2 run time exceeds boiler 1 run time......on and off they go.
My suggestion is to disable the run time compare solve logic until the clock tick changes. (ie. wait till midnight to do the run time compare or use another timer (an additional counter to count)set for,, say an hour, day, or a week). Then enable the run time compare logic. The lead/lag will switch based on the new timer/counter.
Easier yet, if you only have 2 boilers why not change the lead/lag sequence every 12 hours using a timer/counter? If timer/count is < 12 then enable boiler 1 for lead, if timer/count is >12 then enable boiler 2 for lead. Reset the timer/counter at 24. (don't forget zero hour is a number, in this instance)

I hope this has helped you solve the constant on/off switching problem.

Just a bitmore......
 
Last edited:

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