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    Atdemeo
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Sensor CEM3 VAC Scaling and Regulation

Greetings,

I have a CEM 3 96 Touring rack at a semi permanent install for a venue.   We have a number of TR20SAF Modules in addition to the majority of D20 modules.  

I am not sure I entirely understand the Voltage Regulation and scaling features of the Sensor, but I am hoping someone can explain to me.  We have a conventional rig with roughly 75 575w Source 4's in a rep plot with a single circuit per fixture.   The input voltage for the rack lives at around 126V.  I  read about 124 at the receptacle on the truss, after 100' or so of copper.     With the Max Scale voltage, and regulation enabled, I was expecting the max voltage to be the default 115v at the receptacle, not 124v.   If I use a TR20SAF card, the regulation works properly.  It does not work with the D20 cards.  The result is an ever so slight difference in intensity, which doesn't matter in most applications, but is frustrating when it does make a difference.

Why do the D20 cards not react to the scale voltage? 
How does the scale factor come in to play?

Is there a step I am missing somewhere to enable regulation for all of the modules?    

I am using a True RMS meter.

Thanks for your help,

-Andrew

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  • Hi Andrew,

    Essentially (when in regulated mode) the CEM3 has settings you can tweak for :
    - Min scale - the voltage the dimmer outputs when it is at the threshold - usually 1% - so basically the minimum voltage it will output
    - Max scale - the voltage the dimmer outputs when it is at full, at the output lug of the dimmer
    - Scale load - when you load up a dimmer, some voltage is dropped internally, so the scale load tells the dimmer the proportion of the output load to the maximum load of the dimmer. In your case, a 575W lamp (4.79A) on a 20A dimmer means this should be set to about 23%

    The dimmer has a calculation which is made based on the type of module and scale load in order to accurately hit the voltage at the output. Now of course, that's the voltage at the output of the dimmer, and more voltage will be lost through the cable to the load, again depending on the size of the load, the cross sectional area of the cable and the length of the cable.

    I think you should :
    1. Check your module types are set correctly, the D20 and TR20 have different chokes so the drop will be different, the CEM3 needs to know the right module type to calculate that
    2. Check your scale load factor is correct - as mentioned above should be 20-23% for a 575W lamp on a 20A dimmer
    3. Determine the voltage drop between your output and your load; probably easiest to measure to do that. Then you can adjust your max scale values by this much.

    You can remotely alter all these settings in the rack using the Concert software; if you have a laptop, you can run the software remotely to allow you to tweak the voltage while measuring at the lamp end.

    Hope that helps

    -Tom
  • in reply to tomsteer
    It Certainly does Tom. I will give this a shot and report back with results shortly.

    Thanks!
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