For Info - the difference between Analogue, DSI and DALI

Some additional info below to explain more about what I've posted in this other thread : http://www.cbusforums.com/forums/showthread.php?t=2625

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Very confusing this Analogue vs DSI vs DALI stuff eh ?

Not really. Analogue 0-10V and DSI control are basically the same thing. Hard-wired groups of luminaires are given an Analogue or Digital (DSI) instruction to follow. Whatever is physically wired to a particular control group will dim as a group.

So, the only real difference is that Analogue uses a varying Zero Volt to 10 Volt DC signal to instruct the lights what level to go to (where 5V is about 50%), whilst DSI uses a digital (data) signal to define discrete steps (in a similar way to the 256 levels within C-Bus).

The only practical advantage of DSI is that it isn't affected by voltage drop. The advantage of Analogue is that it is supported by almost every ballast manufacturer, whilst DSI is proprietary to one brand (this is not a good thing, as it limits choice).

Note that DSI ballasts can also set the light level to Zero, which sort-of means they can "switch the lights off". This is not really correct because there's no relay involved and the lights are also drawing standby current even if no light is being emitted. Analogue ballasts are specifically designed only to dim to 1-5%, and must be switched off using a C-Bus relay, contactor, etc on the main circuit.

DSI formed some of the basis for the development of the DALI protocol. DALI is available from most major ballast manufacturers and has a far greater feature set... the most sigificant being that DALI ballasts are separately addressable. In all world markets DALI has almost completely replaced DSI. For some particularly strange reason (good marketing by Triodonic probably) DSI still has a strong market share here in Australia, even though it is old, outdated, etc.

So, DALI is completely different - it's not a dimming system, but rather it's a powerful Lighting Control System in it's own right. Think C-Bus, but with less Groups and Unit Addresses per network. So, in reality you do not NEED C-Bus to make a fully operational lighting control system using DALI. It was designed specifically to allow simple systems for offices etc, yet be flexible enough to work great with higher level control systems too.

The advantage of DALI over everything else is that every device is separately addressable - so for lights it's basically like having 1 x C-Bus Dimmer and 1 x C-Bus Relay inside every single light. You give those lights (ballasts) Group and Unit Adresses, and you can change them at any time in the future using software.

So, with Analogue and DSI you hard-wire your groups and then use 1 x C-Bus Gateway channel per "circuit". It's usually best to have a main On/Off Relay channel(s) for DSI, and it's definitely required for Analogue devices.

For DALI you run a control cable around and set up the DALI groups and addresses within devices as you require them. Since the maxium number of DALI devices per (dali) network is 64, you have to bring back 1 pair for every DALI Network, which is then connected to 1 channel of the C-Bus Gateway.

So, say you wanted 10 separately dimmable groups in 1 office space... For Analogue or DSI you'd need 10 C-Bus Gateway Channels, and to hardwire each of those out to the luminaires. I DALI you'd only need 1 Gateway channel and 1 control cable to do the same thing. And you could change the DALI at any time in the future without changing any wiring !

So, considering that ballasts for all 3 systems cost about the same, you'd usually be completely mad to use Analogue or DSI on a commercial job when the more powerful and flexible DALI is available. Further, the DSI system has the disadvantage that you can only get it from one supplier, which apart from limiting your negotiating power also means you are at their mercy for supply.

But the Analogue (and DSI) systems still have a place because they are so simple to impliment - there's no programming of ballasts required and they are simple to understand. DALI is not an easy thing to understand without specific training, whilst Analog and DSI need no training at all.

Also note that some (but not all) Tridonic ballasts can be used for DSI or DALI (so called "FOR ALL" ballasts). But that's pretty irrelevant really considering that no other brands of ballasts can use teh DSI protocol (unless licenced).

Cheers, John

PS : I hope that helps - I typed this in a bit of a rush so it may contain some detail errors. Please advise me if there's mistakes and I will edit them accordingly.

 

John,

This is not so much an error but an omission in your informative post. With 0-10v a big consideration (besides the voltage drop, coarse control compared to the digital controls, need for series relays, and re-strike issues at low dim levels) an analogue (0-10) channel can only accommodate a hand full of light fittings (around 10 depending on whether sourcing or sinking control voltage) compared to 100 fittings per channel on DSI and 64 ballasts on a DALI network.

My understanding is Tridonic developed the DALI protocol then opened it up for all to use. Due to slow take up they then developed a truncated version with the exact signalling method but without the cumbersome addressing - DSI.

Did I mention the method for sending the digital control information is clamping (shorting) the control pair ? A bit like one of those tap thingies they used to use to send morse code, just in reverse.

 

Thanks Phil - always best to have a couple of minds working on this kind of thing ! Some more info below, for people to reference if required...

Theoretically you SHOULD USE a series relay with both DSI and DALI as well. Well, at least as a master control to de-energise each sub circuit when all lights are off (building unoccupied). The reason being that even in a "Zero Light Level" state these ballasts are fully energised, as are the final sub-circuits. It is not "technically legal" (under OH&S) to even change a failed lamp with the circuit energised, yet not-switched DALI circuits could lead you believe that the power was off.

A similar situation to the C-Bus dimmers... they don't really turn "off" either, eh? But the difference is that instead of a trickle current (at 240V) the DALI circuit remains powered at mains voltage and the full current rating of the breaker (up to 20A) which is considerably more deadly This means that there is potentially the possibility that an end-user (or electrician) could assume the power is off (because the switch is off and the lights are off) and be electrocuted when working on the system - for a variety of reasons a lot of electrical work gets done without throwing the breaker

Also, the ballasts draw a couple of watts each while in standby mode, even when the lights are "off". Therefore they don't offer the energy savings that are often proposed if they are never actually switched off - eg: 2W per fitting X 14 hrs (after hours) each day = 28 Watt Hours, about the same energy a running 1 x 36W tube for 45 minutes ! This is can actually add up to quite a large amount of energy in an office tower - 1000 fittings x 2W x 5700 hrs (after hours and weekends) = 11,400 kWh per annum !

I have never personally heard of restrike issues at low dim levels with Analogue systems. But I guess this will depend greatly on the quality of the ballasts used, since some manufacturers might claim (say) dimming to 1% output, yet their ballasts are unstable at that low a setting ! Probably the lowest realistic level would be 5-10% using Analogue, and due to the voltage drop it is hard to get all lamps to appear the "same brightness" at very low levels anyway.

Yes, I forgot about that point and also should add that the number of Analogue ballasts you can use per channel does vary greatly. You MUST check the characteristics with the ballast manufacturer !

The only person who would tell you that is a Tridonic Rep My understanding is that DSI's roots go right back to the Zumtobel LuxMate system from in the early 1990's. But as a proprietary system, DSI could never become "universal" in the same way as 0-10V Analogue was. There was a great need for a "unified" and "open" protocol so all the major manufacturers joined together and formed the DALI group in conjunction with the ZVEI (The German Electrical and Electronic Manufacturers' Association - the equivalent of the Australian AAEMA).

The protocol used by Tridonic's DSI (2 x 8 bit Manchester) was considered to be the best one for use in the new DALI system. As I said before, in all markets other than Australia the old DSI is almost completely replaced by DALI - but here there is so much confusion (and our specifiers are SO SCARED of new technology) that DSI is probably more commonly used even though it vastly inferior.

There's more background info on DALI here : http://www.caba.org/standard/dali.html

I am unsure about the exact method used by the DALI protocol, but I do know that a lot of the DALI ballasts also allow a basic level of control by using a so-called "TouchDIM" or "SwitchDIM" functionality. Basically, this involves applying 240V AC in (morse-code-like) pulses across the DALI terminals, and this will initiate Off/On/Dim commands within the ballasts. Some (not all) ballasts also allow 1 scene (preset) to be set and retrieved this way as well.

One thing to note is that these "extra features" as not part of the DALI protocol, but simply are "add-ons" available from individual manufacturers. Therefore they are not intended to work properly when brands are mixed, since there is only standardisation regarding the DALI side of things. Thus I would not consider using those when interfacing with C-Bus, even though it is quite possible to use a standard relay and some bell press events to control a very functional DALI system !

I also forgot to add that DALI ballasts have a couple of other features :

DALI output devices (ballasts) can store 16 scenes internally, which can be called up as required. This means that the output devices have smarts and the input devices are more simple (compared to C-Bus which is the other way around). Note that more complex scene info can be stored in remote devices if the 16 possible within each output device is not sufficient.

DALI devices can also individually send back status info (onto the DALI network) about their current dim level and lamp status. This is very handy for maintenance purposes, and load shedding scenarios too - and I am pretty sure that the C-Bus Gateway can process this information (but I am definitely no expert on this).

Finally, I made a somewhat misleading comment about DALI ballasts having to be programmed / addressed before use. A lot of them can actually be used in a "non-programmed" state if you want, but they will all be on the same Unit and Group Address (aka Group 255 from the CIS Factory). So, if you don't address them then you'd have to hard-wire the groups in the same way as you'd do with DSI and Analogue. But that would be fine in (say) a small conference room.

Cheers, John

 

0-10v is convenient to dim by using a variable resistor-type dimmer.
one dimmer can control more than 100 lamps at same time. ( usually lamp output 0.5-2ma 0-10v signal current, and one dimmer can sink about 50-200ma current, so you can calculate how many lamps a dimmer can control)
DALI can dim each lamp on bus individually,but only 64 units lamps.
well, 0-10v and DALI can work together use a DALI-0-10v converter, one DALI bus can control 64 units converters or dali ballasts, each converter can control about 100 lamps(dimming at same time), so a DALI bus can control 6400 lamps at last.