Sensor Unique Dimmer Numbers (UD#'s) are a new addressing scheme introduced with Sensor version 3.0 software. Unique dimmer numbers allow multi-rack systems to reference discreet, absolute dimmers beyond 512. In 2.x versions of CEM code, you merely entered a Starting Address for a rack (much like an MPE, a moving light, or an L86 pack). In 3.x code, Each Physical Dimmer in the system is assigned a Unique Dimmer number. A UD# can only be used once (hence the term Unique).
Sometimes it is helpful to relate them to circuits. In a large performing arts center, I may have 864 circuits, spread over nine Sensor racks. Each circuit has a number on it, so that I know what is being plugged in where, and so I can patch it at the console. Each of those circuits just has a number, not a DMX control address. DMX-to-Dimmer control is determined at the rack. I will need two DMX Universes to control these racks, as DMX512 has only, 512 addresses. Unique Dimmer Numbers allow me to address these dimmers using true DMX512 addresses, without any offset math.
That depends on who you talk to. For small-to-medium touring situations, some people like the simplicity of CEM 2.x software, as it allows you to quickly change the addressing of the rack, and it displays the starting DMX address on the main CEM display screen. Note: that this is not as much of an issue with CEM 3.11 code, as you can set the 1st UD when running Generate Defaults, as many tours do.
For touring situations where the rack needs to be discreetly split, CEM 3.x is far far superior (see article S50-R1K-LB7Y How Can I Split a Sensor Rack via its DMX512 Ports?
S50-R1K-LB7Y How Can I Split a Sensor Rack via its DMX512 Ports? for more info).
For large installations, CEM 3.x is better, as the split between DMX Universe 1 and Universe 2 is much easier to work with. Also, you can change addressing of the rack, but there is always a hard reference. The UD# matches the sticker next to it, and isn't affected by a change in addressing. This makes error trend reporting much more reliable.
That equation is for use with 2.x software only. It does not apply to 3.x software. Tuck it away in your brain in case you need it again (hopefully you won't.)
That's fine. If you set the DMX mode to be "Standard", the UD's fall into place without any problem. You set up a Start Address for each rack (automatic in SenEdit), and it applies this start address to the first UD# in the rack. In most cases, the UD# and DMX address are the same.
This is the first UD# in the rack affected by the Start Address of the port. I have an SR6, and I want port A to only affect the first 6 dimmers, and port B to only affect the last 6. Both sources use dimmer numbers 1-6 to affect these dimmers:
Although it can make things a little more confusing, UD#'s allow you more flexibility in addressing.