Sensor strange dimmer curve

We recently bought and installed an old Sensor 24x20Amp portable rack, with an MPE controller (hooked up to an Express 250 board, but I don't think that's relevant).  I've noticed that some dimmers are behaving oddly.

The issue is this: some of the dimmers dim differently than the rest.  The problem dimmers are off at 0%, and full on at 100%, but in between they're noticeably higher than others.

I did some measurements -- using self-test mode 850, and I think with the control board actually shut off, so there's no question about the board having some funny dimmer profile programmed for these dimmers.  And I only measured dimmers that had a load on them at the time - I know measuring the voltage output of a dimmer that has no load can get you a meaningless number.  At 50%, the other dimmers showed 55 volts; the problem dimmers showed 73 volts.

Which dimmers?  Known affected ("bad") are #10 and 11; known good include 7, 8, 17, and 18.  (Those random-seeming numbers that I tested are the ones in the neighborhood that had load on them.)

I swapped dimmer modules around, and the problem stayed with the address, so it's not a couple flaky dimmer modules.

Based on all that, I wonder if it's somehow all the dimmers in that pack that are on Phase B of the three-phase power, since Phase B feeds dimmers 9 through 16.  I tried to test that, by cutting power and swapping incoming power cables A and B, but my notes from that test just say "that made things worse" - I didn't write down my measurements - so I swapped the cables back.

Any thoughts as to what the cause might be, and/or any useful next steps toward fixing it?

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  • There are jumpers on the MPE that need to be set correctly according to rack type and module type.  If they are incorrectly set, the behavior is often similar to the simptoms that you have described. 

    From the informaiton in your posting, I would expect that you have an SP12 (24 dimming outputs) with D20's in it.  IF this is true and the dimmer numbers run straight from 1 on the top to 12 on the bottom without jumping around, then you would need jumpers 1,2, and 8 on with all others off.

    The following link will help you with the jumper settings of the MPE if your rack has a different configuration.

     http://www.etcconnect.com/docs/docs_downloads/manuals/mpeuser.pdf

     

  • Thanks for the reply, and the link!  Unfortunately, your guess is correct (SP12 with 12 D20s - at least I think it's an SP12, the case actually says SP-2420B on the back), and the jumpers are already set as described: 1, 2, and 8 on and the rest off.

    I suppose my next step is to call Tech Support some time while I'm up at the theatre with some test tools.

  • A couple more possibilities to check. 

    1) You mentioned you were feeding this 3 phase power -- Are the internal bus bars properly configured for 3 phase?  (that would be the two small copper plates joining to the middle bus bar rather than the top and bottom bus bars)

    2) Is the phase B led lit on the front of the MPE?  If not you might have a blown fuse.

    Either one of these scenarios would have the MPE trying to control the middle phase of dimmers as if they were powered differently than they are which could yield the results you describe.

    And if those don't work out -- we're in the office 8-5 Central Monday through Friday.



    [edited by: Tracy.Fitch at 11:59 PM (GMT -6) on Mon, Aug 17 2009]
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  • A couple more possibilities to check. 

    1) You mentioned you were feeding this 3 phase power -- Are the internal bus bars properly configured for 3 phase?  (that would be the two small copper plates joining to the middle bus bar rather than the top and bottom bus bars)

    2) Is the phase B led lit on the front of the MPE?  If not you might have a blown fuse.

    Either one of these scenarios would have the MPE trying to control the middle phase of dimmers as if they were powered differently than they are which could yield the results you describe.

    And if those don't work out -- we're in the office 8-5 Central Monday through Friday.



    [edited by: Tracy.Fitch at 11:59 PM (GMT -6) on Mon, Aug 17 2009]
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