PID Corretto

[reubster]

Re: PID Corretto

Thanks JavaB,

This has "bean" a really interesting post, I was convinced it presented the next advancement in corretto roasting and I was a certain contender to try it out.

Its very generous of you to share that info and Im even more impressed at the humble way you allowed your "inventors-ego" to overulled by your Palate.........a true coffee snobber!


Some food for thought: If you had a computer program that "held" a roast profile and in "real time" sampled the measured bean temp against it, The "raise/lower/do nothing" commands could control your triac via a serial port.
Just to keep you thinking....... http://www.national.com/ms/CN/CN-6.pdf

Cheers
Reuben

[JavaB]

Re: PID Corretto

Hi all....

Just an update on the PIDed Corretto....

Whilst it does work very well indeed and is truly "hands free"..... Im not as happy with the results as those obtained using a linear temperature control (moving the heatgun further away.... or my earlier - soon to be current again- high powered triac controller).

After several months of use I have concluded that the espresso produced (well to me anyhow) when using the PIDed roster tastes different.... and have done a few checks.....

The air supply from the heatgun is constant and the PID switches the element on/off every few seconds.... with an even longer off period whilst ramping up slowly to second crack. During the off period the element cools quite quickly (almost no thermal mass to stabilize it) and pumps out relatively cool air.... thus cooling the beans directly under the jet of air..... (When the heater cuts back in, the surface of the bean mass is heated to a much higher temperature before the PID registers the increase also)

The thermocouple.... being buried in the bean mass.... sees this change much later and so reports the temp is still correct whilst the beans on the surface are cooling or being locally overheated...... So you get what appears to be a perfectly smooth increase in temp indicated on the PID.....

But some of the beans are being cooled (those on the surface).... and their temperature can drop by 10 degrees or more before the heater kicks back in....... and that will affect the roasting process and the taste of the resultant espresso - never stall the roast temperature and certainly never let it drop during roasting!

Once aware that this was happening, I tried the thermocouple on the surface....which is a real pain as you need to move it depending on the volume of beans (weight, variety etc).... This provides a somewhat more constant heating of the beans ... but still not ideal.. (and rather impractical)....

So Ive concluded what you need is linear control of the heat output (so the air is always at the same temperature - a ramp and soak PID with linear output (which I dont think exists....)

Failing that a triac control with gerfingerpoken adjustment looks like the best method (or just adjust the height of the gun!)

[Sparky]

Re: PID Corretto



Great to see this finally up and running. I was wondering how the Auber was performing. It actually sounds pretty close to perfect for the job, especially with the ability to store multiple profiles.

Now Ill have to think about taking that next step myself.

Control control.. I want more control....

[robusto]

Re: PID Corretto

Hmm. That WOULD be a good way to utilise the alarm function. Maybe it could also trip a relay to switch on a cooling fan? More digi-tech than reaching over and pushing a button with the finger!

Or, to switch on a tape recorder to play a triumphant flourish. Which would also wake you up.

Ah, the possibilities are boundless.

-Robusto

[JavaB]

Re: PID Corretto

Thanks Robusto,

Its a relatively simple mod and not very expensive....

The PID was about $120 including shipping, the SSR was $8 and the box which houses the PID cost about $8 as well....

It means you can use an inexpensive heat gun (the Ryobi is about $40 and very well built) - and have very fine and repeatable control.

Past first crack its great watching the temperature increase by 0.1 of a degree every couple of seconds... nice and smoothly with no risk of stalling the roast....

I just sit back and let the automation kick in and do the work.....

Now to work out a way of automatically dumping the beans into the cooler at the end of the process :..... there is an alarm output which operates at the end of cycle..... at least it can sound and wake me up if Ive fallen asleep so I can initiate the cool down ;D ;D

[robusto]

Re: PID Corretto

Nice work JavaB. Sure is a nice level to aspire to.

When you mentioned ramp and soak PID and bay of evil, --- I instantly tought "Auber PID".

Yep, pictures confirmed it. Now if you had a Silvia instead of your Cimbali, you could have gone for a twin set.

-Robusto

[JavaB]

Re: PID Corretto

Hi Belinda....

Been at a nieces First Communion.... after which was a family function...

Here are some photos.....

The PID (removed from the plastic box it normally lives in to prevent little -- and no so little :) fingers touching the 240V.... ouchie... ouchie





The red wires on the right go to the Jaycar thermocouple.... There is a relay O/P version and this one - highly recommended... drives a Solid State Relay.

The SSR mounts on the back of the board which holds the heatgun (see posting in heatgun sections for frontal view). It needs to be mounted on a heatsink.... but not as big as the one I used which was a piece of Aluminium U channel I had lying around...



The leads between the SSR and the PID are only 12V signal leads.

The fan (and low temperature element which powers the fan) are not affected by the PID.... so there is a constant air flow into the bowl.... only the main heater element is controlled- and that cycles every couple of seconds to maintain the set temperature.

I personally wouldnt change the fan speed.... as the fan is keeping the HG relatively cool... At the end of the cycle the main heater is turned off and the fan continues to run - thus cooling the HG.... The air from the HG could be used to cool the beans.... but not as effectively as dumping into a colander with a more powerful fan.

[Corretto]

Re: PID Corretto


Java, does the PID control the fan speed to the HG as well or just the heat?

Where are those pictures? Enough time already :


Belinda

[JavaB]

Re: PID Corretto

What exactly does one look for on Evil Bay, eg what is it called?


Belinda [smiley=engel017.gif]

Belinda,

Just search for "ramp soak"..... and you will find the item (international seller).

The Bosch could probably be modified.... but it would be easier with a simple gun - like the Ryobi 2 speed.

[Paolo]

Re: PID Corretto

JavaB
This sounds FABULOUS!!

I cant wait to see the photos.

I want one too!

[Corretto]

Re: PID Corretto


Yes, it does sound exciting. Exactly what I wanted for the setup soon after it came into the world as a new roasting method. Which incidentally is just over one year ago now

This could be a nice Birthday pressie for it [smiley=evil.gif]

I should be able to find someone to do it to, though not sure if the electronic Bosch HG should be used though, probably something lesser.

What exactly does one look for on Evil Bay, eg what is it called?


Belinda [smiley=engel017.gif]

[JavaB]

Re: PID Corretto

Hi Belinda....

Yep, Ill get some photos organised shortly.

Its not too hard to modify the heatgun etc.... but does require someone with some electrical knowledge unfortunately...... check out a your friends, neighbours etc..... Its amazing what you can "buy" for a kilo of freshly roasted premium beans.....

I was super impressed with the results I was getting before this mod..... but after modifying with the PID it is totally "hands free".... just flip the switch and wait for the beans to be roasted - to exactly whatever level you desire.

I cant imagine any roaster doing a better (or easier) roast.....

As Big Kev used to say "Im excited"

[Corretto]

Re: PID Corretto


Sounds Fantastic Java.

I want one and I want it now :-)

Trouble is to find someone to put it altogether for a technically challenged Coffesnob.

Any pictures???


Belinda

[JavaB]

Re: PID Corretto

OK, dredging up an ageing thread :

Ive been roasting for a while now with a PIDed Corretto..... and the results are fantastic!!

The PID is a 30 stage Ramp/Soak unit available on that Evil site for around $100 Australian.... The temperature probe Im using is the one supplied with the Jaycar data logging multimeter.

I have programmed the PID to ramp up the temperature to 150C, hold it there for 3 minutes (to "dry out" the beans) then ramp up the temperature steadily to about 200 degrees fairly rapidly, then to 210C more slowly and then to 230C - VERY slowly....

The output of the PID goes to a solid state relay which switches the heater element of the Ryobi heat gun.....

The temperature set points can be easily changed for different bean varieties..... and you can store about 3 profiles in the PID and select which one you use.....

The autotune function works perfectly with an empty Corretto.... but there is over/undershoot in temperature with beans in the bowl and the PID is autotuned - easily fixed by fine tuning the P I and D values manually....

The results, as mentioned above.... are perfect.. There is a steady uniform start to first crack and then a smooth increase in temperature as the beans approach and then enter second crack. The time for the two stages is 100% repeatable (for a given bean variety) making it easy to pull the roast 10 seconds before, just at, or 10 seconds after the start of second crack.

So for anyone wanting to take their roasting to the next level, a fairly inexpensive and simple solution.

[wrstikoff]

Re: PID Corretto

It would be a fairly straight forward Mod to do but to get the best out of your Corretto, youd need a slightly higher spec controller..... one that has the capacity to introduce several ramp/soak stages through the roast cycle and then to take it a step further, a controller with comms capability as well to allow you to store and run Roast Profiles.

Mal.

Hi Mal,

The controller indeed has comms capability - RS232. The graph is produced from the data capture during the roast. Also used for changing the roast profile

Being new to roasting I dont know about ramp and soak. I can program profiles in 20 second intervals within the limits of the heat gun power output (the yellow line, also captured) and about 26 minutes duration. Any input into improvements in the profile would be hugely appreciated.

For you interest I guess, the controller is an Atmel ATmega8. Which is an 8 bit programmable micro processor.

It can store only one roast profile at the moment (actually 2 - one is hard? (maybe firm :-?) programmed the other is changed using the RS232 (loaded from excel) so I can keep as many profile as I like.

Cheers
Dave