Control/Dimming Followspot Dimming Issues

Joined
Aug 5, 2015
Location
Kalamazoo, MI
Had an interesting problem come up today and I am hoping someone can explain it to me. I am an electrician at a community theatre and some of our followspots are Source 4s on a stick. These are powered with our sensor dimmers, but also have a household wall dimmer so the operators turn their own spots on and off.

Normally, we just park the channel and call it a day; but on this show the LD really wants to vary the intensity of one of the spots and control the fade outs. The problem is when the channel is at a very low level (between 07 and 01), the light suddenly snaps to full intensity. If we remove the dimming switch and plug directly into the circuit it dims the same as any other fixture. I made sure an intensity curve wasn't applied to the channel, tried dimming switches from different manufacturers, different circuits, different dimming modules, and different lights; all with the same result.

So my question is why does this happen and is there a way of getting around it that still gives the spot operator and the LD the level of control they want?
 

RonHebbard

Well-Known Member
Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
Had an interesting problem come up today and I am hoping someone can explain it to me. I am an electrician at a community theatre and some of our followspots are Source 4s on a stick. These are powered with our sensor dimmers, but also have a household wall dimmer so the operators turn their own spots on and off.

Normally, we just park the channel and call it a day; but on this show the LD really wants to vary the intensity of one of the spots and control the fade outs. The problem is when the channel is at a very low level (between 07 and 01), the light suddenly snaps to full intensity. If we remove the dimming switch and plug directly into the circuit it dims the same as any other fixture. I made sure an intensity curve wasn't applied to the channel, tried dimming switches from different manufacturers, different circuits, different dimming modules, and different lights; all with the same result.

So my question is why does this happen and is there a way of getting around it that still gives the spot operator and the LD the level of control they want?
Here're my thoughts, for what little they're worth:
When you wrote "different dimming modules" I presume you're speaking of different local dimmers at the spot and I further presume all the units you've tried have been of the electronic; dual SCR, triac, IGBT variety.
If you can find / source / afford a purely resistive rheostat you may do better.
If a purely resistive local dimmer of sufficient wattage isn't in your future, you MAY get lucky using a local autotransformer of adequate rating depending upon which Sensor module you're using, how you have it set up and how it feels about driving an inductive load like an autotransformer. I've done this with 1500 Watt autotransformer dimmers and old Ward Leonard dual SCR 6 K dimmers but long ago, long before ETC was in business. The autotransformer dimmers had a good feel physically and sat on the catwalks next to the operators where they were convenient to reach and operate. We also applied a couple of small, adhesive backed, rubber bumpers which the operators could feel with their fingertips for specific levels without taking their eyes off their targets. This all worked quite well for a production of 'A Chorus Line' quite some years back. We were also using LED pointers mounted on the spots and shining on white bristol-board charts within the ceiling cove area so the spot ops could accurately pre-position their spots prior to lighting them up. This is a time proven technique from arc Supertroupers where the arc is struck and producing light but the mechanical dowser is shut keeping it off the stage. This manner of pre-marking scheme is obviously useful for many productions but extremely beneficial with a fast moving show like 'A Chorus Line' where you're often nailing head and / or half body shots on the 'auditionees' standing on their respective 'spikes' in their line.
Alternately, if you were to install a SPST, 3-way, switch such that the grounds and neutral remain intact but the operator can switch the spot between the locally dimmed source and the output of your stage dimmers you should have a winner. Two electronic dimmers attempting to operate in series won't be your winning answer.
Toodleoo!
Ron Hebbard.
 
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BillConnerFASTC

Well-Known Member
Joined
Jan 30, 2010
Location
Clayton NY 13624
Ditto Ron's
Two electronic dimmers attempting to operate in series won't be your winning answer.
If your house light system is Unison or Paradigm, you could mount slider stations on each follow spot connected to the system, and then the spot operator and board operator both can have control of the same dimmer, with a selection of logic, like highest take precedence, or board opt takes precedence, etc. Would be quite functional if you need that either operator has dimming function.

I expect in the past these had been parked at full on the console and you avoided the problem. I'm kind of surprised the wall box dimmer on the spot still works and didn't go puft.
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
The core of the problem is that you have a dimmer plugged into a dimmer. This never works out well. The firing circuit in each dimmer relies current leaking through the load to give it the juice needed to gate the SSR. Another dimmer interrupts that path. Although parking the dimmer at full may have worked for you, even that arrangement is unstable. If you want to run the spots directly from the rack, that's fine. If you want to use a local dimmer and plug the light into a wall socket, that's fine as well. But, one or the other, not both.