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  1. #1
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    Jun 2006
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    Honeywell Spyder

    I'm looking to see if anyone has done any sort of rate of change programming in a Spyder. I would like to monitor rate of change of the line temp to hold back staging up. I have been messing around with some programming but not happy with anything I'm coming up with.

    Looking for some logic to produce-
    ΔF/minute comparing leaving water temp vs leaving water setpoint

  2. #2
    Join Date
    Dec 2007
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    I do something very similar in PCT. I use this logic as an upstage permissive. My example is for cooling. If you need heating, switch the Output Low Range to 100 and Output High Range to 0. What this does is if I'm approaching setpoint and there is still a logical call for another stage from a PID, It will only allow the next stage if I'm more than 75% on my span for 5 minutes. This is a redneck rate of change block! Hope this helps.
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  3. #3
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    Jul 2002
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    There are times when a timer may be a good idea but if this is a continuing operational problem you may want to look at the control loop throttling rang and gain. If your loop is too tight and staging things then you can correct just that. If you use a timer then when the other stages eventually come on the loop hasn't slowed and has kept going and may now even be at 100%. Then when the additional stages energize the controlled variable sudden change will cause the loop to overcompensate and drop to 0 shutting things off and causing short cycling.

  4. #4
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    Thread Starter
    Quote Originally Posted by The Reaper View Post
    I do something very similar in PCT. I use this logic as an upstage permissive. My example is for cooling. If you need heating, switch the Output Low Range to 100 and Output High Range to 0. What this does is if I'm approaching setpoint and there is still a logical call for another stage from a PID, It will only allow the next stage if I'm more than 75% on my span for 5 minutes. This is a redneck rate of change block! Hope this helps.
    Thanks that is really helpful.

    Quote Originally Posted by incontrol View Post
    There are times when a timer may be a good idea but if this is a continuing operational problem you may want to look at the control loop throttling rang and gain. If your loop is too tight and staging things then you can correct just that. If you use a timer then when the other stages eventually come on the loop hasn't slowed and has kept going and may now even be at 100%. Then when the additional stages energize the controlled variable sudden change will cause the loop to overcompensate and drop to 0 shutting things off and causing short cycling.
    We don't control the chiller staging. The chiller controls it's own staging. But I can hold off a compressor. The chillers are redundant. We only give a chiller a run command. Just want to hold a compressor off, if coming out of switch over and the rate of change of the CHW is high enough.

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