Switch/Discrete Inputs Assign Actions to Inputs
Z-Max Advanced Programming & Systems Design Guide rac00-sdg
Revision A:11/2005 Page 79
The modes express what happens to the assigned relays/groups at the "ON" trigger
point followed by what happens at the "OFF" trigger point. The On trigger point
occurs as the foot candle levels from the photocell drops and the Off trigger point
occurs when the foot candle level from the photocell is rising. Another way to think
about the modes is that the first part of the mode indicates what action will happen
when the "sun" is rising or getting brighter and the second portion of the mode
indicates what will occur when the "sun" is setting or getting darker outside.
Mode 1, Relinquish On/ Force Off,
is useful for
applications where you want to turn relays on
manually and off automatically when it gets bright.
This mode also allows manual control to turn relays off
and on. This is the typical daylight harvesting
application. For example, think about a classroom
where there is only an on/off switch for use by the
occupants. The teacher comes in the morning, when
it’s dark outside, and turns on the switch. All of the
lights come on. When the sun comes up and natural
light fills the space, the photocell would detect lights
which would pass the trigger point and then turn off
some or all of the lights in the room. When the sun
goes down or prolonged cloud cover exists making the
room dark again, the photocell would detect the
darkness and then turn the associated relays on and
then relinquish
control back to the manual switch
which if in the on position would turn the lights on.
Since up to (16) trigger points for the same photocell
can be programmed, this can be used with multiple
zones of relays to allow different levels of ambient light in the room, or rather multi-
zone control.
Mode 2, Force On / Force Off
, is useful for applications where you do not want to
to allow manual control of the lights at all. The relays come on when it’s dark, and go
off when it’s bright. Think about parking lot lighting, when it’s dark the lights go on,
when it’s light the lights go off and you don’t ever want anything else to override it.
Mode 3, Force On / Relinquish OFF
is useful when you want relays to come on
when it gets dark and then allows for manual control when it gets bright. A typical
application of this would be when you have a parking lot or step lights and you want
the lights to turn on as the sun sets or a large dark cloud rolls in, but you have a
switch in the system for manual override purposes.
Daylight Harvesting
In a daylight harvesting
application, the goal is to
maintain a consistent
lighting level within the
space, regardless of the
source of light which could
be either daylight or
dimmable artificial light. If
this lighting level can be
maintained completely with
daylight, no artificial light is
necessary. However, if the
day lighting is not sufficient
to meet the desired level, it
can be boosted by the
artificial light connected to
your relay cabinets
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