Lightning Control (Deadband)

[Blackhaze]

Hi guys.
Can someone explain to me what is the deadband for that is shown in the powerpoint slide.

here is the link
https://docs.google.com/present/edit...TkwZmpuMno0ZmQ

[digo]

I think you mean lighting control...

http://en.wikipedia.org/wiki/Deadband

The purpose is common, to prevent oscillation or repeated activation-deactivation cycles.

In the powerpoint slide example lights go off when the light level reaches the top of the deadband, lights come on when the light level reaches the the bottom of the deadband.

[Blackhaze]

hi digo
thanks for replying.
But i still do not understand..... why is there a need of deadband?
can you give me an example of scenario to illustrate the whole process?
Thanks in advance

[digo]

Your slide is dealing with an exterior lighting application.
Light level intensity is typically measured in lux or lumens. Although generally speaking the light level will gradually rise and fall from sunrise to sunset, what happens when a cloud gets in the way?

http://elad.lbl.gov/index.php/Photos...ased_Switching

[osiyo]

hi digo
thanks for replying.
But i still do not understand..... why is there a need of deadband?
can you give me an example of scenario to illustrate the whole process?
Thanks in advance

If you read Digo's responses and linked references you should have the idea now.

In outdoor lighting control using a photo sensor we'll typically scale photo sensor's analog output (signal input to a controller) to an arbitrary 0-100%. Actual lumen value being irrelevant to the purpose. As in, "Who cares?"

Zero being fully dark, 100 being max signal from the sensor (full daylight, for instance, altho actually sensors that we use output 100% long before maximum possible daylight).

With the sensors we typically use, we'll set up control to allow outdoor lights to enabled at, for instance, a fall in signal below 25. But they'll not be allowed be disabled again until there is a rise that exceeds 30.

That's a 5% dead band of full scale.

We make those settings user adjustable.

Also, in each case reaching enable/disable setpoints, a time delay is also used. We also make that user adjustable. We use a default of 5 minutes. But user can change that.

Without that deadband, normal and usual fluctuations in ambient light might end up repeatedly turning outdoor lights on an off. Not a good thing. We're not talking motion sensors for security purposes.

And, for instance, a 1% variation in that signal, perceived light level by the sensor ... is NOT something your eyes (and mind) are gonna notice. Unless it were oscillating rapidly. OTOH, outdoor lights rapidly switching off and on ... you WILL notice.

i.e. Imagine typical scenario, you've just pulled up to the office building parking lot in the later evening, got out of vehicle, and are making your way down the walking path towards entry, ready to start your night shift. Just as you reach a couple steps that transition a change in ground level, lights go off. Humans actually have pretty decent night vision. But it takes time for the eyes to adapt to sudden and drastic changes in lighting level. For a moment, you're effectively blind. Thump, thump, thumpity-thump you go.

This tends to aggravate some folks. Might even result in a feeling of "Ouch" and some language you might not use in front of your mother.

With no deadband and no time delay, a transient extra light source detected by photo sensor could trip system from on to off. i.e. passing vehicle with bright lights on, which just happens to hit right spot for reflections to be picked up by photo sensor. Or building next door just switched on its lights. Or whatever.

I say that we "enable" or "disable" outdoor lighting via photo sensor signal, since that's not the only controlling factor.

We also typically include a time schedule. Maybe you only want ALL the outdoor lighting to come on and be on for a finite period. i.e. Place has workers or customers till 10 p.m. so yah want all parking lot and walkway lights on if its dark enough. Until 10 p.m.

But after that, you're "closed". So you want most parking lot and walkway lights to go off. Except for a pre-determined few. Entry lighting, for security purposes, small area of parking lot where night shift people (i.e. janitors and such) can park, walkway from that select parking area to entry door lite up. So staff has some light for security reasons and so they don't go bump in the night. Maybe drive path going around to loading dock so night deliveries can be made. Etc.

We'll typically do lighting controls for exterior lights so user can selectively set them to manual off, manual on, time schedule only, photo sensor only, or time schedule and photo sensor combined. We each such combination/selection controlling groups of lighting. That way owners/operators can change things, set em up to suit their own preferences and needs. That's if we're doing lighting that's strictly on-off control of groups. Installations with variable brightness control is a whole different subject.

Gotta have a dead band in there. Or you're gonna have a mess on your hands. Grouchy people. Plus rapidly cycling lights on and off drastically increases failure rate of the bulbs, starters, etc.

[Blackhaze]

Hey thanks a lot, I think I have understand most of it.....
THANKS osiyo and digo