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Thread: Floating point.

  1. #1
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    Floating point.

    I need help understanding these things guys.

    When I find myself at an airhandler with floating point actuators (24v) what should I look for as far as my meter goes? The largest part of the actuators I deal with are 2-10dcv signal and 24ac power, no problem in the least, but I simply do not understand the concept of floating point. From common to "open" I get the exact same voltage as from common to "close"

    Can anyone explain it or just share a link?

    The one today was a Belimo lr24-us I think but thats just from memory. I don't want you guys to troubleshoot it for me, just help me understand how FP controls get told what to do.....lol

    Thanks.
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  2. #2
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    Quote Originally Posted by Wj Stevens View Post
    I need help understanding these things guys.

    When I find myself at an airhandler with floating point actuators (24v) what should I look for as far as my meter goes? The largest part of the actuators I deal with are 2-10dcv signal and 24ac power, no problem in the least, but I simply do not understand the concept of floating point. From common to "open" I get the exact same voltage as from common to "close"

    Can anyone explain it or just share a link?

    The one today was a Belimo lr24-us I think but thats just from memory. I don't want you guys to troubleshoot it for me, just help me understand how FP controls get told what to do.....lol

    Thanks.
    Floating actuators "float" open and closed by pulsing power to the open or close connections on the actuator. The actuator probably says it has a 95sec runtime so you need 24vac on the open connection for 95sec to be at 100%. To close back down to 50%, the close connection needs to get 24vac for 47.5sec.

    The controller usually pulses 2 electronic switches to "modulate" the damper motor open and closed.

    The short of it is that there isn't an easy way to tell what position it's supposed to be in with your meter.

    If you want to test to see if the outputs are pulsing you could use a 24vac test light and see if it turns on and off. Your meter will read a trickle voltage through the electronic relays so it will look like they're always energized.

  3. #3
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    LR24

    24 volts across Red & Black will drive it one way
    24 volts across White & Black will drive it the opposite way
    No power = no movement

    The L/R switch will swap the direction it moves. The notation near the switch should help make sense of it.

    Most schemes in the controller use the stroke time to figure out where the actuator is.

    Example:

    If stroke time is 60 secs, then powering Red & Black for 30 secs, puts the thing @ 50%. Almost all controllers have some way to sync the actuator to the timing mechanism. Some pulse the actuator all the way to on direction once a day, others will continue to pulse after they have reached 0 or 100%.

    To test something like this, get the controller to move the actuator both ways while checking for power on the two outputs. Of course this whole scheme can get farfed up if the timing is not right, or the controller never syncs with the actuator.

  4. #4
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    Power to open.
    Power to close.

    As everyone said, entering the timing of the motor is very important as the controller needs to know that if it powers the motor open for 45 seconds on a 90 second motor, then it opens 50%.
    Generally, the only time the motor will drive 100% one way is on start up. Once the temperature is satisfied, it will slowly start to power the motor closed in small increments (say 2 seconds) until the temperature needs to be satisfied again - then it will open it in small increments. This is only and example of how it might work in a given situation.

  5. #5
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    Whenever I changeout or test a "floating" or "tri-state" actuator I cycle controller the power off and on after I'm done.

    This will usually re-start the syncronization.

    If I don't do this step then the valve usually stays open (or closed) as the full runtime has preveously elapsed and the controller thinks the valve is where it was commanded it last.
    Last edited by powerhead; 09-05-2007 at 08:04 PM.
    Edited by powerhead on more than one occasion

  6. #6
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    I'm starting to wonder if the actuators I looked at today were out of sync. I did cycle the controller though.
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  7. #7
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    Quote Originally Posted by Wj Stevens View Post
    I'm starting to wonder if the actuators I looked at today were out of sync.
    IMO, that is the weak link in the chain with floating or incremental control.
    It is not uncommon to schedule a calibration sequence for them to ensure they stay in sync.
    IlovemyjobIlovemyjobIlovemyjob....say it with me now!

  8. #8
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    Interesting. Will they always sync up on power up?
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  9. #9
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    Quote Originally Posted by Wj Stevens View Post
    Interesting. Will they always sync up on power up?
    hhhmmm....

    I don't believe I have ever ran across one that didn't, but you never know.

    What type of controller are you dealing with there Mr. Anheuser-Bush?
    IlovemyjobIlovemyjobIlovemyjob....say it with me now!

  10. #10
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    Quote Originally Posted by x-wrenchturner View Post
    What type of controller are you dealing with there Mr. Anheuser-Bush?
    An evil one....lol I think its a trane, the schematic references tracer. I'll get the model.

    I'm gonna scrutinize it in the am by running the stat to both extremes, and recheck the wiring on both actuators... If it don't respond correctly I'll get some numbers.

    When I cycle it , both actuators do move, I'd say about half way, then back..... probably syncing at that time.

    It's just so much easier to rule out the 2-10v actuators....

    Then again its only easier because I don't understand this one I guess.

    x and everyone thanks for your help.
    ___________________________________________


  11. #11
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    lol, I thought there was going to be a discussion on "Floating Point", as in a string of digits/bits...
    I got all excited! O'well...


    Edit:
    Sorry, I guess I could also actually try to help your issue.
    If the actuators are not going through its full stroke when they are syching, the Stroke/Time is most likely set incorrectly.
    Stroke/Time = The time it takes for the actuator to stroke from full clockwise to full counter-clockwise (and visa-a-versa).
    For example if the actuator has a Stroke/Time of 180/60, it means the actuator will move from 0degrees to 180degrees in 60 seconds.
    Last edited by codewriter; 09-05-2007 at 10:33 PM.
    “It is impossible for one to learn what one thinks they already know"

  12. #12
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    I will make a comment on what your meter should read and you may have noticed it. Your meter should read 24v when the actuator is stroking but I will mention that many controllers will bleed voltage thought thier output when you disconect the load off thier output. Specificly if you disconect the actuator to read voltage you may very well read 24v on both the drive open and drive closed output at the same time. The bleed through is not enough to stroke the actuator(although there have been occasional issues I've seen that it is an issue) but will be enough for your meter to read confusing many people.

  13. #13
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    Quote Originally Posted by willf650 View Post
    if you disconect the actuator to read voltage you may very well read 24v on both the drive open and drive closed output at the same time.
    Actually I found this even with the actuator connected.

    Its really the part that confused me, I had read how floating point worked and never looked far into it because it seemed so simple, simpler than 2-10 even.... I just didn't realize my meter would be so useless. But I am understanding quite a bit more with all this help......

    If I initially check one and it will stroke when the controller is cycled, I know it has 24 volts, the motor isn't locked up. If it strokes all the way one way and then the other it tells me it should be syncronized, has full range of motion etc. If not then I need to check the stroke/time on the controller.

    That should be enough for me to turn my attention to the controller unless there is something else you guys would suggest looking for at the actuator.
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