An external probe works well enough if the boiler is insulated. When I was PIDing the Vibiemme, I tracked the external vs internal temperature for a while and it's definitely close enough. A possible advantage of an external probe is the ability to 'optimize' placement after the fact. An internal probe location maybe limited by the mechanics. I needed a soft snakey bend in the probe to place the tip as close to the HX as possible. In retrospect, probably unnecessary.

When I initially installed the PID, I fine tuned it to the point that the boiler varied only a few tenths of a degree at idle. This did not result in optimum performance. Over a series of shots, the brew temperature dropped, even though the boiler was at temperature. It seems that the thermosyphon, at least on the Vibiemme, functions more effectively with some instability. By tolerating larger range in boiler temperature, the repeated shot temperature is more stable.

A PID can set an upper temperature, so that functions as a 'safety'. That coupled with the over-temp breaker and the over pressure release should be enough. If I was to leave the p-stat in the machine, I'd connect it in parallel with the SSR and in series with a honking great switch. By flipping the switch, I'd have instant steam pressure. With the PID, I have to run the set point up. One advantage of the PID is I can 'tune' the boiler pressure for the type of foam, quantity, and cream content of the milk.

The advantages of a PID :
- noiseless operation.
- possibly longer life expectancy.
- ease of adjustment for diverse coffees.

Hi

I've been reading here for a few weeks, about as long as I've had my new Brewus II and one of the things I've not seen discussed is adding a second pump in the thermosyphon loop so you could warm up the group by turning on the pump, that would allow adding a PID to the group that would actually be able to control something. Don't see any reason why it wouldn't work and it ought to be doable without any visible signs. But I'm just a newby here and it's possible this idea's been discussed and discarded years ago.

Ira

Welcome to Home-Barista -

It has been mentioned (in passing) by Sean Lennon but the complexity of the installation, including the sourcing ($) of a small pump to handle the high temperature water casts a small doubt on its effectiveness AS COMPARED to flushing a few ounces of water through the group to heat her up a touch.

No experience with this but just my 2 cents and foggy memory.

Edit: - If Sean did it, I'm sure it is effective however what I meant to imply is that this sort of espresso machine engineering is beyond the reach of most of us.

Ken Fox wrote:A PID temperature controller, or any controller for that matter, is not going to work well if what it is controlling is far removed from what it is measuring. The "what" it is controlling is of course the boiler element.

I am however finding that my current system allows quite a bit of accuracy and reproducibility of shot temperatures, so any additional improvement would be small and probably not worth the effort involved.

ken

Say Ken,

Since you've made more than one or two posts over the last few years (which means quite a few come up when doing a search), can you review for the discussion what your current setup referred to above is?

I know I read about one of your Cimballi projects a while back but don't know if it's the final-final.

Thanks,

M./

maximatica wrote:Say Ken,

Since you've made more than one or two posts over the last few years (which means quite a few come up when doing a search), can you review for the discussion what your current setup referred to above is?

I know I read about one of your Cimballi projects a while back but don't know if it's the final-final.

Thanks,

M./

I have 2 Cimbali Juniors; one is a vibe pump manual pourover model, circa 1995



which I purchased new and have subsequently modified with a PID temperature controller which functions in place of the pressurestat, which was removed in order to have a port for entry of the SS ensheathed thermocouple probe.

The other machine is a ~4 year old, current version, Cimbali DT1 rotary automatic model



which was also purchased new, and has been modified with both a PID controller for the boiler, plus a delay timer which produces preinfusion at around 3.5 bar for around 6.5 seconds, before the pump engages and produces 9 bar for the remainder of the shot. Vibe pumps by their very nature have a slowly ramping up pressure profile, so there was never any reason to modify the plumbing on the old vibe machine.

Both machines are operated at a relatively low boiler temperature, most of the time around 230-232F (a little hotter in the old vibe machine) which, after a 50 ml flush, produces a shot extraction temperature of around 198F. This boiler temperature PID setting produces a front panel gauge reading of about 0.7 bar. I can, if I want, produce shots at approximate temperatures of 196 to 204F by choosing the boiler temperature setpoint on the PIDs, however I generally prefer a shot temperature of around 198F for the coffees that I tend to drink.

Here is a recent set of shot temperature curves produced on the old vibe machine. This is not bad temperature control, for a simple modification on an almost 13-year old machine, for which tight temperature control was never a design consideration!



I use the rotary machine the majority of the time, as it is fully plumbed in and somewhat more convenient to operate, although for about 1 week per month I turn the rotary machine off and use the vibe machine. Both machines are seldom on at the same time, however I do have them both on when conducting simultaneous shot blind tasting trials, something I do from time to time, and have done most frequently with Jim Schulman.

ken