Vibiemme Double Domobar PID tuning

December 1st, 2012, 2:38 pm

Gerry on Sun Aug 28, 2011 6:09 pm wrote:As promised, here's a very brief summary of my journey into VBM PID land. I noticed that the stock setting of the PID caused an oscillation between 198 and 201 F, when set at 200 F, with a 2.5-minute period. Using the Wikipedia tuning process http://en.wikipedia.org/wiki/PID_controller and the Ziegler-Nichols method outlined there, this suggests that the "P" was set about right, the integration constant "I" should be 0.01 instead of zero, and "D" should be 15 instead of 0.5. I have been using these PID values for a week now, and notice that without disturbance the temperature stays within 1F of the set point, and overshoot is somewhat less than with the stock values. That said, it's not worth the bother changing them unless you are particularly compulsive or just like to play because the minor improvements are doubtless invisible when it comes to temperature stability of the shot. This is dominated by the large mass of the group head, as has been often pointed out. The bottom line is that whoever determined the original PID settings for this machine did very well indeed.

Had my DD week and a half now and was researching tweaking PID to primarily improve intershot recovery. Stock settings recovery just too slow for my liking even with steam boiler on pre-heating brew boiler inlet. Found your old thread and tried your settings.
(Old thread won't allow replies anymore hence this new thread.)

Not only is idle temperature more stable but intershot recovery time better too. Thanks

I do disagree with "it's not worth the bother changing...". Simple and quick to change and so far definitely seems improved performance both in stability and recovery. Very worth it if someone has moderate barista skills and mandatory if fast barista skills.

December 2nd, 2012, 9:19 pm

Been tweaking the P-I-D settings a bit more going for a balance between aggressive recovery and stability.

For now settled in on P=1 (factory default) I=0.03 D=15. Even with an 8oz mega flush dropping it 5f no overshoot coming back up.

P much higher recovery fast but overshoot too much, @1.5 a whopping 4f (with I=0.01 D=15). Then had I up to 0.05 with P=1 D=15 but again too much overshoot though only 2f. Didn't try I=0.04 since overshoot so much @ 0.05 and so far 0.03 seems a good balance between agressive without overshoot. At idle it just sits there about 80% of the time @ set point 20% 1f below. How boring!

During pull boiler displayed temp may and sometimes not drop 1f. (This is with steam boiler on for brew boiler inlet preheat)

Unfortunately my Scace Thermofilter currently busted so no real geeking out for now.

Oh, and pulled some mighty tasty shots this rainy Sunday including a delish Panama Esmeralda Boquete Geisha doppio.

#3: Post by **decaf_Ed** » December 5th, 2012, 6:45 pm

FYI... I got a 6-degF overshoot with D=15 (as opposed to the usual 2-degF, over and under, with the factory settings), so I dropped it down to D=5 and things seem better. I haven't seen more than a +/-1 degF variation so far. I'll try raising D again later and see if I can repeat that +6-degF behavior.
-Ed

December 6th, 2012, 11:53 am

Weird, with P=1.0 I=0.03 D=15.0 over shoot +6F?! Most I've seen extremely rarely 1F usually nada over shoot. This morning after pulling a couple doubles and post 3x water pf wiggle and back flushes pulled some more through to dump temp down 10F, still came up with zero over shoot. On first settling down very briefly drop 3F, then back up to exact temp target, then briefly down 2F back up exact target, then settled to (seemingly for me) usual mostly at target down 1F now and then.

If I start a shot when just coming up from 1F low to set temp occasionally see 1F displayed over shoot during shot if a tight pull, but seems almost never any over shoot at idle.

#5: Post by **decaf_Ed** » January 4th, 2013, 10:37 am

Compass Coffee wrote:Weird, with P=1.0 I=0.03 D=15.0 over shoot +6F?!

Apparently on my machine, when turned off for a short time (like one minute, +/- 300%), there's often a big temperature overshoot after turning back on. That's the only big overshoot I've seen, now that I've been looking for overshoot. I wasn't looking for any overshoot before I changed the PID values, and only noticed this afterwards. The "short-off" overshoot seems to be less at D=15 than at D=1 or 5, so I've returned to D=15, with no reason not to. Steady-state temp is more stable, and transient recovery is also better.
So, yes, thank you!

-Ed

#6: Post by **Spitz.me** » January 4th, 2013, 2:06 pm

WOW....

I used

PID Setting wrote:P=1.0 I=0.03 D=15.0

I remember passing my machine occasionally it was usually recovering, it didn't really stabilize for long enough, I guess. Now, I've passed my machine randomly over the last 5 hours and EVERY TIME it was at the SET TEMP. That's quite different than before. As well, changing the temp up 1F I saw temp, almost instantly shoot up without an overshoot. Before when I made a change it seemed to take more time to stabilized with an overshoot.

I would say this setting is MUCH better than the default, makes the VBM DD more nimble.

#7: Post by **LaDan** » January 5th, 2013, 4:14 pm

I should try this with my Duetto. With the temp set to 200°F, the oscillation are between 197°F to 203°F, and the boiler indication bulb lights up at 198°F and turns off at 200°F.

Noticing that all these machines use the same Gicar brand PID, I wonder if the setting is from Gicar and not from the espresso machine factory. So in that case Gicar is setting them for all and they are all the same.