Vivaldi mini temp regulation vs PID

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Johnlyn

Vivaldi mini temp regulation vs PID

Post by Johnlyn »

All right, I've tried searching but I am apparently not finding the right words to get the answer I am seeking. So I ask your help.

I just want to know what is used in the Vivaldi for temperature regulation. The Dream uses a PID but I can't seem to find out what the Vivaldi uses and I am curious about advantages and disadvantages compared to a PID? There must be a thread on this already so apologies if I am asking a question that has already been beaten half way to death...
Endo

Re: Vivaldi mini temp regulation vs PID

Post by Endo »

You can Google PID, but basically it refers to a control loop feedback system. In the case of an espresso machine, it's a control loop on temperature between the temperature sensor and heater in the boiler.

The term PID in the espresso world usually means one of the many generic off-the-shelf controllers you can buy for about $50 (like the Auber Instruments PID I installed on my Silvia).

The S1 also has a tempertaure control loop feedback system. But instead of installing an off-the-shelf PID unit, LaSpaziale decide to build the temerpature control feedback logic into the controller board IC (which was already there to control other machine functions such as button and alarm functions). This makes perfect sense to me.

People make the mistake of assuming that by installing a PID, the temperature control will be much better. In fact, the temperature stability of the entire system is far more important and complex than the rather simple water temperature control. The shot stability has to do with the thermal dynamics of the system. Like how much mass is in the group head, the temperature loss going from the boiler to the grouphead, or the flow rate of the cold water introduced. These factors have already been tuned very well on the S1. You can easily see this in the many Scace videos online which show you the rock solid temperature stability of back-to-back shots on the S1.

Thw PID on the S1 is more about marketing, not so much about science. It will add very little to the S1 except to convince some new users they are getting a better espresso shot because the pretty LCD now has an extra decimal place. :roll:

When the new Dream comes out, I challenge anyone to make a Scace video showing me its any more stable than before.

If they were seriously interested in improving temperature stability and accuracy, they would have added a PD controlled charge heater in the grouphead like on the new Breville so that the first shot would not require 2 warmup flushes. :evil:
Johnlyn

Re: Vivaldi mini temp regulation vs PID

Post by Johnlyn »

Thanks for that Endo. That does make sense regarding a whole system approach. But how does the functioning of the temperature control loop feedback system differ from a PID? PID's have been marketed as the holly grail of temp stability and as a result I have no idea how another system would work or even what they are called?

I was also surprised that there were no changes to the group with the Dream. I also would have thought that there would have been a PID grouphead control. The Breville is sweet for that, rock steady stable and quick warm up. I still flush before a shot though, 6 secs, certainly not two shots. Some forums however have been arguing against the flat temp profile that the BDB provides. However, the Vivaldi is quite stable so if it ain't broke, don't fix it right.

Ideally I would love a machine like the BDB with the commercial quality and reliability of the Vivaldi.
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chas
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Re: Vivaldi mini temp regulation vs PID

Post by chas »

The V2 is pretty much limited to a simple calculation as to what it does a) thermostat indicates water temperature below set temperature b) turn heater element on until water temperature equals set temperature c) turn heater off.

A PID does three separate calculations before deciding what to do a) a straight forward math calculation 2) a differential calculus calculation 3) an integral calculus calculation. It is effectively looking at what is happening right now, what the effect of the output was on the input during similar past occurrences, and based on those inputs what it thinks it needs to do to replicate successes or prevent errors in the future based on past events.

One of the PID settings actually defines at outside temperature range - say 5C. If the water temperature is more than 5C off from the set temp the PID turns on the heater element and leaves it on until the temperature is within 5C. Then it starts pulsing the heater element on and off at a slower rate so that the temperature does not overshoot the set point. When the temp is right at the set point the PID pulses the heater element at an even faster rate to maintain a steady temperature. I had a V1 for two years, then a V2 for two years, and now a GS3 for 3 years. As I recall, when the V2 is sitting idle and up to temp, the group boiler would turn on for something like 5 seconds every 30 seconds or so. In the case of the GS3, it turns on for about 1 second ever 5 seconds.

Also, PID'd controllers use thermocouple temperature sensors good to +-0.1 degrees. I think the V2 actually uses either a thermister or else a diode sensor which are good for about +-1 degree. In spite of all that, the V1 and V2 do an excellent job maintaining a stable group water temperature.
Chas
LM GS/3 & LaSpaziale Dream v 1.25 (US 120V)
Mazzer Kony E, Customized Rocky
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Johnlyn

Re: Vivaldi mini temp regulation vs PID

Post by Johnlyn »

Thanks Chas, that is the clearest desciption of a PID that I have ever read. It sounds quite sensible and idealy I would have purchased a machine that controlled it's temp that way. Are there any down sides to a PID?

I do however, like the idea of the simplicity of the V2's system. to my electronically ignorant brain it sounds like less to potentially go wrong.
Endo

Re: Vivaldi mini temp regulation vs PID

Post by Endo »

chas wrote:The V2 is pretty much limited to a simple calculation as to what it does a) thermostat indicates water temperature below set temperature b) turn heater element on until water temperature equals set temperature c) turn heater off.
Chas. How do you know there is no feedback logic in the V2 controller board? I agree it does not turn on the heater as often as my PID'd Silvia, but who's to say logic built into the S1 board is not recording last reading and determining slope? Are you saying the temperature swing is simply controlled by a sensor with a tight deadband?

And if that is the case, isn't this good enough given all the other variables in the system I described? Obviously it is not enough on a Silvia (with a 10 deg stock deadband), but I have yet to hear one serious professional say they can differentiate any less than the current 1C (which is the current deadband on the V2).

They should call this topic "The princess and the Pea - ID". :roll:
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