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Thread: Floating point.

  1. #27
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    Runs in one direction for the amount of time programmed, no more, no less.
    You are correct, if someone physically moves it/slippage/etc..., its most likely going to stay "out of wack" until it goes through it calibration.
    “It is impossible for one to learn what one thinks they already know"

  2. #28
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    Wow floating point is about beat to death! This should become a sticky.

    >When it calibrates ... does it indeed sense the resistance when it runs into a mechanical stop, or does it simply run it in one direction long enough that it knows it should be at full stroke?

    Varies manufacture to manufacture. One thing is sure, they don't measure resistance or anything that fancy. Typically they will overdrive the actuator by more than enough to be sure it’s all the way. ie if its a 90sec actuator it may be driven for 120 to sync it.

    Another method is to just keep pulsing the output when the controller thinks the actuator is 100% or 0%.

    Some controllers will take a feedback from the actuator, pot or contacts. Haven’t seen this method much lately.

    Floating point is meant to be cheap, nothing more. 2-10v or 0-10v actuators cost more, and when you need 100+ for VAVs etc it adds up quick.

    >most people do have an extra 24vAC relay banging around somewhere, so its a quick and easy tester. I can hear people laughing at me now... O'well

    Ditto, I like the RIB relays as emergency backups. Dual voltage 24/110 coils with indicator light make them especially useful.

  3. #29
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    Many that I have seen (where I know the software) tend to drive the output closed for twice the specified drive time when the unit moves out of occupancy.
    There was also a manual stroke routine to achieve the same effect. It really ought to be automated so that it can be periodically nudged, in my opinion.
    gnomethang
    _______________________________________________
    "Once men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them."
    - The Reverend Mother Gaius Helen Mohiam

  4. #30
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    In case anyone was curious....... when looking at the program with "Anywhere" it showed one valve with a stroke time of 30sec.......... should have been 110 or 120, when changed it operated good. Thanks for the help all.
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  5. #31
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    Glad you found your problem!
    “It is impossible for one to learn what one thinks they already know"

  6. #32
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    You have snatched the pebble from the hand!

    Very good grasshopper.
    Edited by powerhead on more than one occasion

  7. #33
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    happy to help you

  8. #34
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    Quote Originally Posted by rolo View Post
    happy to help you
    How did you help? I believe all the credit for help goes to the people that actually read the thread and posted responses pertaining to the thread.

    It is nice to see that you didnt call something junk or recommend Robertshaw for a change.
    Quote Originally Posted by Qui-Gon Jinn (Star Wars Episode 1)
    "The ablilty to speak does not make you intelligent!"

  9. #35
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    Oct 2007
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    An important step that hasn't been mentioned is how to test the triac with a meter in the absence of a relay or the time to wire one in.

    Triacs will leak, sometimes almost as much voltage as it would take to energize a coil on a relay but just enough to not. You need to measure the voltage at the triac, in this example 24.7v. Then measure the power source for the board powering the triac, lets say a transformer. We will fcall that the reference voltage. If the transformer is putting out 28.1v then the relay should not energize until the triacs output voltage is equal to the reference voltage.

    As far as testing the actuator at the actuator, a lot of times we would ire 24v to the common and we would switch the ground of each output, open and close. Measure common of the actuator to earth ground (the can) and if it is good then jumper that common 24v to the open and it should stroke open, repeat for close.

    Hope it helps.

  10. #36
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    Cool.........thanks
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  11. #37
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    Floating actuators aren't just cheaper as a reason to use them on large quantity applications like VAV, they are better than modulating for VAV. The life is much longer and the floating is more accurate with small repositions.

  12. #38
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    Why is a floating point going to last any longer than an analog actuator? A 0-10v is going to compare the input to its current position. If they differ it moves, otherwise the motor is at a stop. I guess the position pot could wear out. I’ll ping our rep for the MTBF between these, you sparked my interest to see if this theory holds water.

    More accurate, only if your controller can track the time accurately enough and pulse its outputs for < 1/3 second when needed. Belimo’s analog versions have 256 steps over the stroke they can land on. That’s .37deg increments you could modulate to if necessary. Trying to move it in smaller increments I would think backlash in the gear train is going to throw off the position. This would make trying to position it that accurately useless.

    I would be interested in hearing a story how moving a VAV damper by <0.4&#37; of the total stroke solved a comfort issue. Grossly oversized equipment?? Not trying to be arrogant, just realistic.

    BTW I based my math on the LR24-3 that sparked this thread. 95deg stroke in 95 seconds.

  13. #39
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    I agree, if you have to constantly reposition a vav damper to maintain the airflow setpoint, it means the rest of your system is not setup properly.

    Personally, I like analog better than floating for many reasons, however as most people, I use floating vav actuators for many other reasons...
    “It is impossible for one to learn what one thinks they already know"

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