Dim curve MDT KNX dimmer (0201.01) very far from linear

[Leo]

I installed a second hand MDT AKD-0201.01 dimmer on my KNX-bus in a Loxone setup.  With the help of a YouTube tutorial, we succeeded in configuring the KNX addresses in the device successfully with a demo version of ETS.  After integrating the addresses in my Loxone setup, we got it all working.

However, I have an issue with the dimming curve: at 2% it kicks in (=ok), but around 5%, the lamp is almost at full brightness (visually).  The remaining 95+% hardly changes the brightness further (just a little tiny bit).  The curve defined in the MDT dimmer settings is "linear".  Choosing either ohm load, or LED trailing edge, or LED leading edge does not change anything.   We tried an old filament light, a 230V halogen lamp and a 230v GU10 LED... all the same issue.

We were not sure which EIS type to use in Loxone.  We started of using "Dimming/Position EIS6 (DPT5) (0-100%)" which seemed like a logical thing to use.  Also tried several of the others like "Dimming EIS2" and some others.  But other than with EIS6, the light either did not work, or remained at full brightness.

EDIT: forgot to mention we drive it with "dim absolute" (1 byte, number 3 and 18 on the KNX config)

We don't know anymore what else we can try.... anyone can help to get the dimming curve working in a linear way?  

Thank you,

[Duncan]

a linear curve wont give a linear appearance of the dimming as our eyes perception is roughly logarithmic

if the dimmer doesnt have a suitable curve then you can do it using loxone

change the light block so thats dimmer type is 0-10v

connect the 0-10v output of the lighting block to both inputs of a multiplier block

connect the output of the multiplier block to your knx output

now the maximum output is 10x10 = 100% but the curve will be exponential

any better?

[Leo]

Thanks, Duncan.

I changed the curve in the dimmer to "Logarithmic", but strangely enough, no visual difference to this setting at linear (weird).

Then I tried your solution with an analog multiplier, connecting the output of the lighting controller to both AI and O2, and that worked.  The light still gets too quickly too bright, but it's workable.  I tried doing this analog multiplier another time after the first one, and now it's quite OK.

Thank you very much for your assistance.... really appreciate it.

[Duncan]

its quite common to use x3 instead of x2 - try it

you can do this using a formula block or 2 multipliers together, and youll have to scale the output from 1000 back to 100 - you can use the correction feature of the knx actuator for that to keep things simple