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Thread: Floating point.

  1. #40
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    >constantly reposition a vav damper to maintain the airflow setpoint, it means the rest of your system is not setup properly.

    Ditto, you have other issues to look at. Also moving an electronic actuator in this manor will reduce its life regardless of the type.

    And the word from Mr. Belimo on the life expectancy of the different types…

    “No difference.

    We test all the actuators the same. The new generation non-spring actuators, i.e., LMBs, are all tested for 100,000 full open-closed cycles and 1,000,000 partial cycles.

    I don’t see any noticeable difference between the -3 and –SR.”


    That’s lines up with what I have seen over the years. Properly applied and installed they will most likely outlast the controls driving them.

  2. #41
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    Thumbs up Intgeresting Thread

    Double post. My apologies.
    Last edited by whec720; 10-07-2007 at 01:46 PM.
    "Nearly all men can stand adversity, but if you want to test a man's character, give him power."
    -Abraham Lincoln

  3. #42
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    Thumbs up Interesting Thread

    Learning a lot from this thread. I'm by no means a controls guy, but have looked up why floating point is claimed to be superior at less wear than that of an analog actuator. I'll let you guys debate the facts and will just shut up and read. Great posts, BTW.

    This system and method receives input command signals from an actuator controller, and effectively integrates these signals until the controller has requested a large enough movement of the actuator that the actuator can actually effectuate. At this point, the system and method drive the actuator to the commanded position. As a result, excessive mechanical wear in the actuator caused by small command signal perturbations and dither is reduced or eliminated.
    "Nearly all men can stand adversity, but if you want to test a man's character, give him power."
    -Abraham Lincoln

  4. #43
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    I've never tried it, but couldn't you use a clamp-on ammeter on each of the actuators "open" and "close" wires to see which has the greatest amperage?
    Then compare it to the common wire amperage for reference.
    jogas

  5. #44
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    meter use

    I have two d.m.m.'s on my truck, a Fluke 179 & a Fluke 16.
    The Fluke # 16 has a feature that they call lo-z or something like that. If you connect to a triac with the meter in ohms range it'll auto-switch to this lo-z mode and dampen the "ghost voltage" to a reading of zero, if the triac is closed (on) then the reading will show the voltage like a normal meter would. My 179 was expensive (for me) but I grab the less expensive 16 ($120.00) 90% of the time. I used to use the relay test until I discovered this feature on my meter.
    RealEyes
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  6. #45
    Join Date
    Oct 2005
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    ...........I OFFICIALLY PROCLAIM ALL YUS.....NERDS!

    A 4-page thread on FP?!!!!

    bUT i LOv IT.....
    IF YOU BUILD IT...THEY WILL COME!!!...

  7. #46
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    Quote Originally Posted by whec720 View Post
    Learning a lot from this thread. I'm by no means a controls guy, but have looked up why floating point is claimed to be superior at less wear than that of an analog actuator. I'll let you guys debate the facts and will just shut up and read. Great posts, BTW.
    In the case of the common Belimo actuators, I believe the mechanical parts are essentially the same between the analog and floating point actuators. What is different is simply the built in electronics of the device. I could be wrong. I've never asked Belimo. But I have disassembled a few non-working actuators out of curiosity and the mechanical parts looked identical to me.

    I'm personally unconvinced that there is any significant difference in wear over time between the two, based upon any difference in design.

    However ...

    I have on a number of occassions seen situations where an analog Belimo actuator was doing some excessive hunting (minor, continual movements) as a result transient, induced voltage fluctuations on the signal wire. Exact source of the induced fluctuations, I most often did not determine. <Shrug> No time to fool with it and investigate.

    When such a situation was found, I'd usually ensure that ....

    1. Common on the actuator 24 VAC power supply and common for the signal source ... were in fact common to each other.

    2. Check for differences in ground potential between equipment at which the actuator was mounted and where the controller was mounted. ie At one job site controller was mounted (and grounded) inside building envelop inside a storeroom and Belimo was attached to a rooftop unit. Actuator was "wandering". I ran a wire from controller enclosure up to roof and attached it to RTU metal. Checked with voltmeter, from ground of controller to ground of RTU and found a varying voltage differential. Only a few volts, but it was there. Bonded my temp wire to frame of RTU and to same ground controller used. Problem went away.

    3. Occasionally have found small, nuisance induced voltage on signal wire (yes, it was shielded and shield drain wire connected to common at controller) which was corrected by simply readjusting minimum output voltage of controller analog-out signal from 2.0 VDC down to 1.8 VDC (for example). How and why small fluctuations were occurring despite a constant commanded voltage output ... who knows? I don't. Doesn't happen often but I've seen it, time to time. Usually haven't the time to investigate in detail.

    I've noted that floating point actuators, by the nature of how they work, don't have this problem. Rock steady, transients don't effect them.

    But as noted, either analog or floating point motors CAN BE severely affected and excess wear occurs if the control loop allows too frequent position readjustment (hunting). I always purposely design in a slow response in the control loop and a healthy deadband. After all, does it really matter, in the case of dampers and valves, in average comfort HVAC applications, if one sets up a control loop that allows a half degree, or even a full degree, of temperature swing off setpoint before a valve or damper moves? The fact that you CAN control to much tighter tolerances ... does NOT mean it's a good idea. Or even worthwhile. Is the increased wear and tear worth the results? Not often.

    Just my opinion, worth no more than that.

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