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Electronic Theatre Controls Inc

Using multiple Echo Light Sensors in a single space

Question

Can multiple Echo Light Sensor (E-LS) stations be used in a single Echo space? When multiple stations are present do they average together? Does it make a difference if they have the same or different programming? 

Answer

The short answer is that yes, multiple Light Sensors can exist in the same space, but they do not average with each other. The long answer follows below, but first note that an Echo Light Sensor is comprised of two parts. One is the controller (dome), which the PCB is attached, and the second is the sensor head. A single controller can have TWO sensors heads attached (usually one at the controller and one located remotely), and in that case the controller does average between the two sensors heads to control the lights. The info below only applies when we're talking about multiple controllers in an Echo space.

When multiple controllers exist in a space, only one of them can be active for each given Echo zone. This means if the stations are configured to control separate zones (Zone Raise/Lower, or Zone Set to Level), then each will function independently of the other. When they're configured to control the same zones, or are set to a Space/Preset action (which inherently includes ALL zones in an Echo space), then the following occurs:

  1. Each sensor sends an arbitration message on the Echo bus every 5 seconds, stating which space/address they're set to, along with which zone(s) they're configured to control. For each zone all the sensors determine a group which sensor has the highest priority. If any zone has overlapping control, the lower priority sensor(s) will go inactive and cede control to the highest priority sensor. Priority is determined by the following rules:
    1. Sensors with a lower native space will have priority over sensors that have a higher space, when spaces are combined (i.e. space 10 is a higher priority than space 13)
    2. Sensors with a lower address will have priority over sensors with a higher address (i.e. address 3 is a higher priority than address 8)
    3. If zone control does not overlap between sensors, they both have control in a space
  2. The highest priority sensor will send a status message to control the lights every 5 seconds. If a previously lower priority sensor has not seen an arbitration message from a higher priority sensor after 1 minute, the lower priority sensor will reassert control over the space/zone and start sending its status message. (NOTE: if the sensors are located in separate physical locations, each will control the room slightly differently since detected lux levels may be different in each location.) If the original highest-priority sensor's arbitration messages are seen again, they will re-arbitrate based on rule #1.
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