BeArd: I sense an XY problem here.
What are you controlling with the SSR? If you don't absolutely need phase angle control, you probably don't need a 0-20ma input SSR.
I'm controlling heater. I understand, that I can simply take 60sec and turn it on 3-10-50sec, but that is not so good move, because when heater is fully on, it give too much heat, so the product burns.
I'm not good electronic, and don't understand fully "phase angle control". I just need to make heater work not on full power (some time 10%, 30%,..100%)
Ok, here are your options:
-Buy or make a PWM to 4-20mA converter. I am not sure if there are any commercially available ones, and the price may be the same as the VMA420.
-Use the VMA420 and feed it with a filtered output from your arduino.
-Use a short time-base PWM to drive a simple zero-crossing SSR. (I say short because you mentioned up to 50 seconds. This is quite long in terms of heating control, and a virtual eternity in terms of microcontrolers.)
The last one is what I would do for a heating process. If 3 seconds on will burn the product, it is no problem to turn on the SSR for a fraction of a second. In fact, I would set the time base at 3 seconds!
I have read this post like 10 times,
You must have a lot of free time ...(I'm still on my first read... 
)
This is a fascinating post. I had no idea a 4-20 mA current loop was that complicated. I've never tried to
create one before. Maybe I'll give it a shot now...
I found this.
FYI,
(The OP is lemming)
That link has several solutions, did you mean this one?
Yes
lemming:
I want to make my arduino mimic an industry standard 4-20ma sensor.I understand that the load that it will drive (PLC, VSD, etc) are usually around 100 ohms.
Has anyone got any ideas on the circuit that would be required to do this?
@lemming, it's been a while since you started this thread, but did you end up with success? I am limited by time and have no experience with building circuits, so the best I can come up with is this transmitter (but they are pricy.)