Ramp times

Discussion in 'C-Bus Automation Controllers' started by ssaunders, Sep 13, 2022.

  1. ssaunders

    ssaunders

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    I think I understand ramps. Happy to be corrected.

    On a NAC/SHAC, if an object/group is at zero, and I specify a SetCBusLevel to 255 over eight seconds, then the ramp takes eight seconds.

    But if a group is zero, and I set it to go to 127 over eight seconds, then the ramp takes four seconds, being the time it would take getting to 127 on its way to an ultimate level 255, which it will never reach.

    The same goes for an eight second ramp of 127 to 145, which is an eventual total ramping time of around 0.6 seconds.

    So is this correct logic? Ramp = ramp rate, which is not the same as time to transition from one state to another.

    School me for why should my thinking be busted.
     
    ssaunders, Sep 13, 2022
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  2. ssaunders

    Ashley

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    Correct. That's why it's called a ramp 'rate' not a ramp 'time' :)
     
    Ashley, Sep 13, 2022
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  3. ssaunders

    ssaunders

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    :D:D:D

    And "I think I understand" instantly turns into "Yup. I got it." Thanks @Ashley. I can not believe it's been over a decade until I've actually really looked at the detail of a ramp (rate). :oops:
     
    ssaunders, Sep 13, 2022
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  4. ssaunders

    Ashley

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    Some more useless information:
    There a 16 ramp rates because the ramp rate is enconded using 4 bits in the protocol.
    The intervals are counted in about 16mS increments (can't remember the exact figure), so with a 16 bit counter you have a maximum time interval of 65536 * 16mS = 1048576mS = about 17.5 minutes, which is why 17 minutes is the longest ramp rate. Made it easy to implement in the original (slow) microprocessors of the late 90's.
     
    Ashley, Sep 14, 2022
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  5. ssaunders

    Ks04

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    I've actually always wondered this! I'd love a ramp rate less than 4sec
     
    Ks04, Sep 14, 2022
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  6. ssaunders

    ashleigh Moderator

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    And if you look at DALI by comparison you will see that many things there use FADE TIMES, which are real times, not rates.

    For example with a fade time of 4 seconds, a fade from 0 to 254 (in DALI, level 255 is magic), would run for 4 seconds. But so would a fade from 10 to 12. Or 19 to 73. Or whatever.

    This is one of those things that makes the translation of cbus ramp rates to fade times VERY difficult, and any match is usually a matter of luck rather than anything else.
     
    ashleigh, Sep 14, 2022
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