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Electronic Theatre Controls Inc

Voltage Regulation in Sensor and Unison DRd Racks


The information in this post is provided to assist in troubleshooting. Perform work at your own risk. ENSURE ANY POWER FROM DEVICES HAS BEEN DISCONNECTED BEFORE SERVICING ANY EQUIPMENT. If you do not feel comfortable performing the work, please contact us or your local service center. Be aware that ETC and its Affiliates are not responsible for any damage or injury caused by service of our products by anyone other than us or our authorized service providers, and such damage is excluded from the product’s warranty. Please follow all NFPA70 guidelines.

What is voltage regulation?

In a line-voltage dimming system, there are many factors which affect the total voltage at the load. Voltage may be unsteady, causing loads to appear to flutter, and voltage drop over long wire lengths can result in loads having noticeably different output depending on which circuit they are connected to. ETC dimmer racks, using Voltage Regulation, can compensate for these issues to ensure consistent output to each of your loads.

There are a few adjustments you can make available in Sensor racks and Unison Paradigm DRd racks. These adjustments can be made but do need to follow a few rules:

  • You can only use voltage regulation to trim the top end of the dimmer.
  • You will need at least 5V of headroom between incoming voltage and what is set as max output voltage. If there is not enough headroom, voltage regulation will have no effect.
    • Long wire runs may require more headroom.
  • You can set the maximum voltage of the rack type (140V for US racks and 280V for CE or HSR racks), but if you do not have that level voltage coming into the rack, you will never get it out of the rack. Unfortunately, it is impossible for a dimmer to increase the voltage output to the load.
  • Do not mix load types on a dimmer if you are making these adjustments.  While it may improve one load type's performance, it could degrade a different load type on the same circuit.

This process of regulation works great for incandescent loads.  It does not work well for most LED drivers, as LED drivers use the pulse width to determine output level.  If we are modifying the pulse width to change the area under the sine wave, the LED driver will interpret this information as a change of level. This can cause normally "steady states" in the output to cause the LED to waver. In these cases, voltage regulation should be turned off for the dimmer. 

Procedure - Setting the Best Maximum Scale Voltage

  1. Pick a point that you want all your dimmers to be trimmed to; this will want to be just below the lowest level that all your dimmers can reach. Since wire length is one of the largest determining factors, it is best to start on the circuits with the longest wire runs and work your way back from there.
  2. Connect a True RMS meter to the circuit at the point where a fixture will be plugged in, along with a fixture of the appropriate load type. Using an adapter to connect the meter between the connector type being used (stagepin, Edson, Twist-lock, etc) to the connection to the distro and the tail of fixture, is a good place to do this. 
    Why do I need a "true RMS" meter? Voltage is voltage, isn't it?

    SCR dimming modules work by rapidly opening and closing an electronic relay using a Pulse Width Modulation (PWM) signal, such that only part of the AC sine wave is output to the load (See here for more info). The longer the relay is closed during each half cycle, the higher the output level of the dimmer. If line voltage increases, the total voltage output over time to the load will also increase, even if the pulse width stays the same.  By compensating for fluctuating voltage by adjusting length of the pulse width, we can keep the output of the dimmer consistent. When metering this output, we need to meter the area under the sine wave as opposed to the peak voltage. In order to calculate this, we need a meter that will measure the root of the mean square voltage of the sine wave, or RMS. Most RMS meters will  specifically say “True RMS” on the label if they are able to read this calculation.

  3. Place the meter in line and take the circuit to full. 
  4. Let's say your voltage going in to the racks is 121VAC.  If the voltage at your longest circuit is 111.5VAC, then 110VAC would be a good place to trim to.  In this example, adjust the output of the dimmer to read 110v at the fixture, then you do this same procedure for all the circuits you would like to be at the same level of voltage.

CEM+, CEM3,  and Unison DRd racks  

To trim voltage output on a Sensor CEM system Unison Paradigm DRd racks, the adjustments are all in Dimmer settings.
Per Circuit: Turn regulation on and change max scale voltage to adjust output. This # is in volts but will not exactly match the # on the meter because of voltage drop on the line.   This operation can also be performed in Concert, but it will not be a live change.

CEM Classic

3.x software there are less options for voltage adjustment. Regulation was always on unless you chose Switched or as an output, Non-dimmed (is a On/Off output puts but still regulated) Setting Max dimmer output was called “Scale Voltage”
2.x software there are even less settings available. Setting Max dimmer output was called “boost voltage”

See control processor manuals for more specific directions.

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