DALI exponential curve

I need to replace some existing dimmers with DALI controlled lamps, via a DALI gateway.

As I understand it, the level sent to a DALI ballast has an exponential relationship with light output, so that setting a level of 60% (C-Bus group address value) achieves only about 10% output level.

What is the best way to map these? Does anyone know the formula for converting between the two formats?

 

The problem I have at the moment is that any level I set from 60% downwards gives me the minimum output level from the fitting. On the C-Bus dimmers I obviously have a huge range of output levels for values below 60%.

It's not the non-linear mapping of numeric "level" and output power that's causing a problem, it's that anything on the C-Bus side below 60% is mapping to a value at or below the minimum 10% for the hardware.

Regarding 4: the fittings in this case are LED, although I have no involvement in the choice of (or installation of) the fittings, just the commissioning.

Note I'm using an old DALI gateway for the trial we're currently undertaking, with old firmware (4.6.0?), so if the old firmware is the problem I'll get a newer gateway installed.

 

it is more likely a control gear issue with the DALi led driver, they dont like to dim to all dali arc levels in my experience.

they will go low and then sometimes flicker a little.
also the visual dimming range from minimum to maximum is from about 60% up.

but these can change through the type of dali control like manufacturer etc.

so you ned to experiment to get the desired result.

try setting the the percentage through your dali configuration software and compare a 60% dali from dali, to a 60% command from the gateway I think you will find them to very close
also ensure the dali ballast/driver levels are set to defaults to ensure minimum and maximum levels are not close

 

Hello Mark
I have more questions than answers about this so I hope you don't mind.
When you say that 60% on CBus equals 10% on DALI, is that being reported from the DALI commisioning software and how are you checking the CBus level?
I have attached a picture of a 4.6.0 DALI interface network settings which is working for me on some 18w fluro downlights.
It has been so long now that I struggle to remember but I was having a problem before I enabled the match ramp rates and status correction causing the CBus ramp and DALI ramp to be out of sync and was having all sorts of trouble trying to set a level from a key input.
The LED DALI fittings sound interesting.
Can you describe the performance of the fittings aside from the dimming curve.

 

If that's the cause of the problem, then I can relax as I didn't choose the kit! (Actually it's quite easy to "fix" in code for this application as I can put my own scaling into my logic, I just need a way to calculate that scaling. It might well be that I just play with a lux meter and "guess" at the scaling.)

 

I'm using a Tridonic USB-DALI interface to commission the kit, with their software (I forget what it's called). It allows me to send a raw decimal value to the dimmed output, as hex 0-FF or dec 0-255. I find that anything below about 170dec gives me no change in output level (tested using my eyes). When I set 170dec the software shows that as "10%", and looking at the light output that seems about right.

When I then send changes via Toolkit to a group address mapped to that output (actually it's mapped to broadcast for now), I find that anything below a value of around 60 (ie 60%) has no effect on the output. This broadly agrees with the effect of writing 170 in the DALI software (170/255 is in the same ballpark but isn't actually 60%).

The trial at the moment involves a single fitting sat on the floor in a power room but the next stage of the trial will be to swap out some existing fittings with the DALI LEDs and compare the two, and the idea was to have them mapped to the same group addresses as the existing dimmer channels so that they dim together; obviously that's not going to work if 60% on the LED fitting roughly equates to 10% on the C-Bus dimmer. However regardless of whether the full range matches (nobody expects them to properly match), my problem is just that we'd normally test at 0%, 25%, 50%, 75% and 100%, and the LED fitting at present will be at minimum level for the 25/50% tests and not much above it for 75%.

I therefore need to add code on my next site visit to calculate the appropriate LED output to match the C-Bus dimmer output as closely as possible. Recalling that my 60% at the C-Bus level equates roughly to 10% at the DALI level as reported by the DALI software, and that being roughly 60% of the full linear range 0-255, I "just" want to start with the same algorithm the DALI software is using to tell me I have 10% when I have set a decimal value of 170.

(This all gets very confusing, I know. I have C-Gate mapping a raw 0-255 value to 0-100% in a linear fashion, such that all I'll ever usually see withing Toolkit is 0-100. I assume that if I set 50% in toolkit that means 128 at the raw protocol level, which would then be mapped directly as 128 to through the DALI interface, and therefore be the same as setting 128 in the DALI software, which would then tell me that I'd set a level of around 7% (as a guess, I don't have any kit here to play with). But I feel like I'm making a lot of assumptions there already!)

Thanks for the picture, it does help. I also had to set the match ramp rates; the level was changing without it but very slowly, and it didn't seem to match up with my expectations from having set the ramp rate directly with the DALI software, but I didn't play with this for long, I just let the DALI interface take over.

I know very little about them at the moment other than that they hurt your eyes if you're staring at them at close range when they come on at 100% unexpectedly during testing.... I'll see what info I can find out when I'm back on site though.

 

This is useful. Sounds like I need to do some lux level tests and not trust my eyes. The manufacturer has said they ship with 60% minimums but can be configured to go lower, but having set the DALI minimum to 1 I still can't get them to go lower in output. (Doesn't help that I'm not talking directly to the manufacturer but going through several levels.)

For what it's worth I think the manufacturer is Phillips.

I have, but the interpretation of the results depends what you look at. When I have software telling me I have a level of 170/255 = 10%, and the 170/255 (66%) broadly matches my experience from sending 60% through the gateway, but 10% clearly does not.

PS: What DALI programming kit do you guys use? It's not something I do often enough to know what's best but I had two Tridonic USB interfaces, and one has died, so I really ought to get a replacement, but there's no reason it should be like-for-like, especially since (like here) I'm not always using Tridonic ballasts.

 

Since I have a serial interface I used DALI tool but I think this one might be more suitable for the USB interface.
http://www.tridonic.com/com/en/911.asp

 

Yep, that's the one I have! Not sure if I have the latest version so I'll grab that in case, though. Thanks!

 

In case anyone else cares, the DALI-USB cable seems to work fine under Windows 7 64-bit, much to my surprise, using the latest masterConfigurator (which has replaced configTool) from here:
http://www.tridonic.com/com/en/2192.asp

Assuming you have an old DALI-USB you need to use the new software via XP first to upgrade the firmware so that it can work with Vista/Win7, but that was all fairly straightforward (=automatic).

 

DALI curve

Seems that most DALI lights are at their minimum brightness when C-Bus is at or around 50%. And there is a logorythmic response between 50-100%.
This should not matter too much if you are setting the lights to preset brightness levels, as you can just tune your scene settings to whatever C-Bus level between 50% and 100% that gives the brightness you want.
Whatever the light goes to at C-Bus50% will be the minimum brightness level of the fitting, which is set within the DALI software / i.e. not a C-bus parameter.
Even with dimming buttons this still should not matter, the maths of how the two systems interact is not that relevant when all it needs to do is brighten up when the dim up button is pressed, and stop brightening up when the dim button is released. i.e. as per previous response, suggest trying it before wondering to much about the different response curves.
Unless you actually need to modulate the light power the different response curves don't really matter all that much.

 

Imagine a mixture of fittings in the same room, some on DALI, some on C-Bus dimmers, all controlled from the same C-Bus group address.

That's pretty much where I'm at.... (It's more complex than that in practice, of-course!)

The levels are set from a head end control (via C-Gate) and I do have flexibility there, so if I have different group addresses for my C-Bus and DALI lamps I "just" need to know what value to set my DALI group address to for a roughly equivalent value of the C-Bus group address.

At the moment I have mapped the C-Bus 1-100% levels to a DALI level 65-100% (linearly), but I'm not expecting that to be very accurate. As things are, the DALI fittings are cabled up on a test rig not in the actual room so I can't fine tune it until they're mounted properly, at which point I could really do with having a proper plan!

 

Ouch..

That would be a tricky one I think as the CBus control will tend to be linear while the DALI will be non linear. So depending on where you are on the control curve, a 5% jump for a C-Bus light will have quite a different effect for a DALI light. Factor in the different properties of the lights themselves and this could be quite a chaotic system to modulate under a proportional control type of system.
A mapping process could be made to work it might not be a non linear setup. You could try having a series of scenes for 10%, 20% etc, and use a seperate group for the CBus lights to the DALI lights. And then manually tune each scene by 'feel' and/or with your lux meter. You would need some programming to cycle up and down through the scenes. It could be made to work but it is probably going to need some logic and some manual setting up of whatever form of 'ramp mapping' you settle on,

 

I'll make it work one way or another!

It would be really helpful to find some documentation regarding the non-linear mapping that DALI uses though, I could at least use that as the starting point.

 

I guess you are thinking along the lines of a relationship approach, i.e. when C-Bus says 80% go to (80% x Dali Factor)..
Have not found documentation to give you a direct relationship like this. Suspect also the relationship would be different between different light fitting types.
If it is flouro's you find that the useful dimming curve is between 50-100%.
And within this the effective dimming curve ( that produces noticable changes ) sits generally between 55% through to a touch over 90%
So if you made say 10 scenes and a new group for DALI lights.
Call the scenes 10%, 20%, 30% etc through to 100%. And have the scenes trigger when the C-Bus group is in the corresponding bands.
Then all you do is set the 100% scene for DALI 100%.
The (0 to)10% scene at DALI 50%.
And just manually set a spread of DALI percentages for the scenes in between.
As a method this will work, is fairly robust and does not require you needing to work out the DALI mapping at a maths level. It is also easy to adjust for any future work.
There are other approaches but I would suggest this as the most simple, especially given you are integrating with an existing install.

 

60% minimum level means the min brightness can be about 10%.
DALI ballast have a parameter called physical min level, usually set min level less than it will not reduce brightness. usually the min brightness of fluorescent ballast above 5%, that means min level will be above 100/255.
some LED drivers may can have a min brightness of 0.5%, so min level can below 25/255.

Any ballasts and programing kits of any brands is similar.

 

Thanks for this information.

Don't suppose you have a formula to convert between the two? Ie given that I want 60% of the maximum brightness, what value should I send to the ballast?