La Marzocco Linea Mini User Experience - Page 35

#341: Post by **pcrussell50** » July 21st, 2016, 3:46 pm

I am degreed in mechanical engineering, (though I never worked in the field). I know the difference between discrete steps and continuous variability, and how digitizing an analog signal has become increasingly standard, as with music and photography, and electronically commutated electric motors in model cars and planes, to name a few. I was under the impression that the LMLM's PID was acting on a digital voltage controller. You're saying the LMLM's PID controls a rheostat? Color me surprised, but OK. I still am not sold on "the wheel", as a user interface for the temperature controller on a machine of this class and price...

... As per this LMLM owner's analysis:

Simon345 wrote:Have had some time now to play with the temp adjustment. Thoughts:

1. I would have preferred a simple display that indicates target temp, along with 2 buttons to increase and decrease temp. I dont think that necessarily makes me a lesser person. The click wheel is clumsy, simple as that. The idea of a manual click wheel to control a digital PID screams out at me that the marketing department insisted on having enough annoyances in the 'cheap' $4,500 model that a portion of users would still aspire to purchase the GS3.

2. The wheel feels cheap when its rotated, particularly when it reaches the end of its travel in either direction and seems to spring back to the touch instead of coming to a solid stop. At this price point in the prestige equipment market the ability to make coffee isn't enough, the machine should comprehensively 'feel' like a $4,500 machine.

3. There should be an update to the user manual that describes clearly how to adjust temp

4. The only number on my temp wheel is 96c which was at the 6 o'clock position when the machine was first delivered. From there, there are just un-labelled notches in the direction of red or blue. Would certainly prefer if it has to be a wheel, that at least each degree Celsius is marked. This makes going back to a known good temp for a given coffee way too clumsy. You cant easily just go back to 92c with a batch of beans because that worked for the beans last time. You have to remember that it was 16 clicks or whatever into the blue zone from the 96 marker. Thats just silly.

5. The temp does seem to change quickly. Set as far as it would go into the blue, and waiting a couple of mins the shot was sour and lemony. Set as far as it would go and all the way into the red after just a couple of mins the group head was hissing steam during a flush to reflect the approx 102c it was set to.

I do like the overall machine though. Apart from a some complaints re: the approach to temp adjustment, the machine feels very solid. The fit and finish is great. The steam is as amazing as I had heard pre-purchase, and the coffee is very tasty.

I have read little (nothing) since this post to convince me he is wrong. Particularly the bolded part, as I have become quite fond of easy and precise adjustment of temperature, when dialing in a new bean.

-Peter

#342: Post by **bluesman** » July 21st, 2016, 4:25 pm

pcrussell50 wrote:digitizing an analog signal has become increasingly standard, as with music and photography

The digitization of audio by pulse modulation of an analog signal is not the same as the pseudo-digitalization of voltage control by using discrete resistance steps to vary it. A digitized audio signal is an approximate recreation of analog source with missing pieces - a replica of the input is being created at the output using filters and algorithms to approximate and add back the signal missing from the gaps between pulses. A digitized image, like a digitized audio signal, is a true digital map that has to be converted back to an analog file to be viewed as a picture. But once the resistance in a circuit is set, the voltage is neither recreated nor approximated - it's determined by Ohm's Law, and the voltage drop across the resistances in the circuit is the source "signal" and exactly the same whether you use discrete resistances or a simple pot to vary resistance.

Digitized sound and image files are not perfect replicas of their analog sources because they remove and recreate some of the content. But whether you use discrete or variable controls to set the voltage in a circuit, what you get is exactly what you want - you just have less fine control over the setting process if you "digitize" the controlling resistance element.

pcrussell50 wrote:You're saying the LMLM's PID controls a rheostat? Color me surprised, but OK.

The PID doesn't control the pot - the pot determines the set point for the PID. Although it functionally controls the flow of current through the heating element, the pot's not physically in series with the element. The pot (like those "digital" button controls) determines the set point for the PID, which physically controls the flow of current through the element.

And I'm not the one saying that the wheel's a pot - LM says it in the manual:

#343: Post by **nuketopia** » July 21st, 2016, 4:42 pm

As I have pointed out before - the temperature adjustment wheel on the *US* model, has a graduated dial.

Outside the US in some markets, LM have decided to use a non-graduated dial with a single marked point. ( I don't think this is a good idea)

The mechanism is a potentiometer, with a regulated DC reference voltage and measured by the ADC on the controller board. The thumbwheel is relatively large in diameter and has a spring-loaded ball-bearing detent.

The machines are factory calibrated by applying the graduated sticker to the wheel after measuring the brew-point puck temperature with a test fixture. (ie. a SCACE device) Thus the boiler temperature + brew-head offset is considered into the calibration of the scale on the dial.

Each click is a small fraction of a degree. Given the range of the dial, the mechanical detent system and the relative stability in other such resistive control/sensing systems, the system is entirely capable and entirely suitable for the purpose of producing espresso.

I can find no data or evidence that shows people can clearly taste relatively small increments of brew temperature in double-blind testing. Thus it is unlikely that any imprecision or drift will result in substantially different flavors in the cup.

I'll challenge anyone who claims such to prove it in double-blind testing.

#344: Post by **pcrussell50** » July 21st, 2016, 6:15 pm

bluesman wrote: The PID doesn't control the pot - the pot determines the set point for the PID. Although it functionally controls the flow of current through the heating element, the pot's not physically in series with the element. The pot (like those "digital" button controls) determines the set point for the PID, which physically controls the flow of current through the element.

So the PID doesn't cycle power to the element on and off, in a narrow band around the set point? Sounds like you're saying it continuously varies voltage (R = V/i), like it sounds like you said in your first post:

The temp wheel on a Linea Mini is a simple potentiometer (continuously variable resistor) that sets temperature by changing the voltage in the heating element.

, right? And the only continuously variable analog voltage control I know of is a variable resistor/potentiometer. What am I missing here in your description?

Anyway, I, like Simon, don't like the wheel. And I haven't heard anthing yet to convince me otherwise.. Not a deal breaker, just an irritant.

-Peter

#345: Post by **Beezer** » July 21st, 2016, 6:33 pm

Some people like the wheel. Some don't. I don't think either view is right or wrong, so go with what you prefer. A GS/3 may be more your style, since you can adjust temp with a display and buttons to give you some feedback.

Personally, I like the wheel because it's fast and easy to use, and it gives more than enough fine control to adjust the brew temp to get the taste I like. I consider it easier to use and more intuitive than most of the PID controls my old e61 dual boiler machine (Izzo Alex Duetto II), which was a bit awkward for me to use as it was right between the hot group head and the hot water valve. It was hard to reach without burning myself, then required a bunch of button pushes to get to the temp setting function and adjust to the temp I wanted. Then I had to wait a few minutes for the boiler to reach the new temp. As a result, I rarely messed with it. Now with the Mini's wheel, it's so easy and quick to adjust the temp, and the results are so clear in the cup, that I adjust it fairly often if the taste seems a bit off.

I think the only thing that I don't like about the wheel is that it feels a bit cheap and plasticky to the touch. It would be nice if it seemed a bit more solid and high quality, both in the material used to make it (maybe aluminum or Bakelite instead of cheap plastic) and in the feel when it moves. However, this is a very minor nitpick. In reality, I don't think about it much because it's pretty much out of sight and I only use it for a second or two when temp adjustments are needed.

#346: Post by **nuketopia** » July 21st, 2016, 6:37 pm

pcrussell50 wrote: Anyway, I, like Simon, don't like the wheel. And I haven't heard anthing yet to convince me otherwise.. Not a deal breaker, just an irritant.

-Peter

Can't see what the big deal is.

I can read the time by the hands on the clock just fine. Same for the tach and speedo in the car.

#347: Post by **LATrapp** » July 21st, 2016, 6:51 pm

Beezer wrote:Some people like the wheel. Some don't. I don't think either view is right or wrong, so go with what you prefer. A GS/3 may be more your style, since you can adjust temp with a display and buttons to give you some feedback.

Personally, I like the wheel because it's fast and easy to use, and it gives more than enough fine control to adjust the brew temp to get the taste I like. I consider it easier to use and more intuitive than most of the PID controls my old e61 dual boiler machine (Izzo Alex Duetto II), which was a bit awkward for me to use as it was right between the hot group head and the hot water valve. It was hard to reach without burning myself, then required a bunch of button pushes to get to the temp setting function and adjust to the temp I wanted. Then I had to wait a few minutes for the boiler to reach the new temp. As a result, I rarely messed with it. Now with the Mini's wheel, it's so easy and quick to adjust the temp, and the results are so clear in the cup, that I adjust it fairly often if the taste seems a bit off.

I think the only thing that I don't like about the wheel is that it feels a bit cheap and plasticky to the touch. It would be nice if it seemed a bit more solid and high quality, both in the material used to make it (maybe aluminum or Bakelite instead of cheap plastic) and in the feel when it moves. However, this is a very minor nitpick. In reality, I don't think about it much because it's pretty much out of sight and I only use it for a second or two when temp adjustments are needed.

I agree with this post. Before using the wheel I was a little worried moving on from a PID. I'm now completely happy with it and would choose it over a PID in the future (although I would also like something other than cheap plastic). Ambient humidity, temperature, rest time etc. all have such an influence that I find myself dialing in easier and better with the wheel than when I used to think 'oh, this bean is a 202f'.

Much like my grinder- if I get a gusher on a first pull of a new bean, I'm not counting out the steps to adjust. I've seen enough shots at this point to just give a quick grinder adjustment and be pretty close without counting.

#348: Post by **bluesman** » July 21st, 2016, 8:44 pm

pcrussell50 wrote:So the PID doesn't cycle power to the element on and off, in a narrow band around the set point?

You said, "You're saying the LMLM's PID controls a rheostat?" The PID does not control the rheostat - the rheostat controls (i.e. determines the set point of) the PID.

Bottom line: I and many others think the use of a continuously variable resistor to set the PID is fine. It's no less accurate or controllable than the film-button PID control units found on so many lesser machines - it simply makes great sense. LM demonstrates once again that less is more - it's difficult to be simple.

#349: Post by **pcrussell50** » July 21st, 2016, 9:22 pm

bluesman wrote:You said, "You're saying the LMLM's PID controls a rheostat?" The PID does not control the rheostat - the rheostat controls (i.e. determines the set point of) the PID.

And in turn, the PID controls the heating element... how? Through what mechanism? Cycling voltage on and off at high frequency as close as possible to either side of the set point.. A continuous series of high frequency, discrete steps... As I have already said, when we started this circle... And as LM says in their own description of how a PID controls the heating element. Agreed that the wheel or push buttons that sets the PID is neither here nor there for performance... I'd rather set a specific value, than count clicks to know where I am... Not a deal breaker, just an irritant... And I'm not the only one who feels that way. If there must be a click wheel, one that sets a digital readout so you don't have to count clicks, would be dandy.

Anyway...

Chris from LM, PM'ed me with answers to my questions from yesterday. As I suspected, I'll be looking for a true commercial machine, if I want 220v, plumbed, with an externally mounted pump as all three of these are either not available and not feasible in the LMLM.

The LMLM sounds like a nice and innovative machine. Because of the innovative aspects, I'll keep following this thread. You guys enjoy your machines. Thanks for the info and interaction so far.

-Peter

#350: Post by **LATrapp** » July 21st, 2016, 11:58 pm

pcrussell50 wrote:I'll be looking for a true commercial machine, if I want 220v, plumbed, with an externally mounted pump as all three of these are either not available and not feasible in the LMLM.

-Peter

If your commercial machine outlined above happens to have a click wheel instead of a digital PID keypad, you'll love it!!