Strugs wrote:Tom - do you recall if the WEGA E61 hex bolt is an M6 metric bolt? I took my bolt out of my machine today and brought it to home despot to try to match it. The M6 seemed pretty close, but it did not want to go into the grouphead easily. I did not torque it much for risk of stripping the threads.

Thanks.

My Isomac uses an A6 as well. It looks like that is a relatively standerd size for this.

I am not fortunate enough to own a Wega, just my little millennium. I run my Pstat high, 1.4 on the top end. I have to run a long flush, your 10oz sounds close to what I do. I get about 12 seconds for recovery (brew water is 201) beyond 18 seconds it is to hot, 25 seconds and I get steam/water mix. I make a lot of milk based drinks so I want the extra steam power, which is why I run so hot. Down side, lots of flushing.

I plumbed in the water supply but no waste water plumbing, just that big drip tray. I usually flush into my cappa cup and dump it in the sink (keeps the cup very hot). My recovery is just long enough to walk from the machine to the sink and back to the machine which is perfect, unless I get distracted (my sink and machine are across the room from each other).

I'm very intrigued by this, mainly because of the relatively low price-point of the parts. I've been following the discussion on coffeed as well, but don't have posting privileges there (yet).

A couple thoughts:

What does the device measure?

The device likely measures the temperature of the head much more than the water. I suspect this as the thermal mass of the probe itself is relatively large, which is then welded to the bolt (which is in contact with the rest of the head), so a few ml of water flowing past it isn't going to change its temperature much.

Is this an issue?

Depends on what you want to measure. The brew heads "work" because their thermal mass is so much larger than that of the water whose temperature needs to be "tweaked" as it flows to the portafilter. If the goal is to determine or set a repeatable point for brewing, measuring the head temperature "makes more sense" to me than measuring the water temperature.

Is thermal lag an issue?

Thermal lag of the probe itself, and the measuring device in general. Yes, thermistor probes generally have higher time constants (or "rise time") than thermocouple probes. Probes with more thermal mass are always going to react slower than those with less. Again, the question is the purpose of the measurement. I don't believe anyone measuring much finer than 1-second intervals and what is the value for the home barista? You aren't designing a feedback control system for the brew temperature. You're observing it do whatever its going to do in response to your technique.

I've read some disparaging remarks about the response time of these inexpensive thermistor devices, but until I measure the rise time of one, I'm withholding judgement.


Measuring "rise time"

I'm going to try to pick up a Taylor 9842 (food service) thermometer this weekend and make some rise-time measurements. As Cannonfodder has pointed out, the absolute accuracy isn't that important (even high-end T/C meters are not much better than 1 deg. F), but repeatability is. The Taylor can be user-calibrated if you want, from my discussions with the manufacturer, and runs $15-20 through a variety of retail outlets.

Rise time is generally taken to be the time it takes to go from 10% to 90% of the change. For most systems, it is reasonably independent of the magnitude of the change. Since we're typically talking only around 10 degrees F, that last 10% is within 1 deg. F of the "final" reading.


Thermocouple-based approaches

Past that, if I get nutso, Omega can custom-fabricate T/C probes with S/S sheaths from 1/8" down to 0.010" diameter, and probably in a reasonable length. Prices on the stock 6" long probes are under $30, with or without a connector attached. They can fabricate them down to a 2" probe length at bascially the same price, with about a two-week lead time.

http://www.omega.com/ppt/pptsc.asp?ref=JMTSS&Nav=tema07
http://www.omega.com/ppt/pptsc.asp?ref=JMQSS&Nav=tema04


They also have handheld meters for about $85, and if you want something flashier/neater, the 1/32 DIN controllers are about 1" x 2" panel size start at around $169 for the "plain" ones, mid $200s for the fancy ones with color-changing displays and computer interfaces.

Even the "best" T/C meters are only accurate to about 1 deg. F plus the probe errors unless you spend a lot more money for a calibrated probe. Many are 1% of reading, or even 1% of range, often additionally plus/minus one or two degrees on top of that, which could be several degrees.

If you're trying to convince me that you "know" your brew temperature is 202.5 degrees, you've got a hard sell with even this kind of gear. On the other hand, if you're saying "it seems a degree hotter than before" then you're probably safe with the statement.

http://www.omega.com/ppt/pptsc.asp?ref=CN132&Nav=temp03
http://www.omega.com/ppt/pptsc.asp?ref= ... Nav=temp03


Pre-fabricated adaptors

Omega's compression fittings unfortunately all seem to use pipe threads, not screw threads. One possibility may be to take existing fittings, turn them down in a lathe, then thread them. This seems excessive.

http://www.omega.com/ppt/pptsc.asp?ref= ... Nav=tema07

I had thought about the heat transfer from the GH via the bolt to the probe housing. The probe I used has a step down at the end. It necks down a couple of 32's. The hole I drilled is to fit the larger 1/8 OD. Inside the bolt there is a small air space surrounding the tip, which contains the resistor, from the bolt body. The probe end that contains the resistor also extends beyond the end of the bolt about 3/16 to help separate it from the heat transfer from the bolt to GH contact. I actually get a very large swing in temp which would suggest there is some validation in my guess. Otherwise you would not get more than a couple of degrees variance in your probe temp during the shot. I regularly get 10-20 degree changes during my initial cooling flush of say 10oz, depending on idle time.

The thermometer I used has a one second sample rate with a 1% of range accuracy. I have stated before that this was never intended to be a 'high precision' instrument. As you allude to, and I posted on my comments at coffeed (I should check back, haven't looked at the board for several days now) the cheaper TC's are not much better than a good thermometer given the purpose of the assembly. I can spend $30 on something without any issue, but if I spend $200 on just a TC, the wife would string me up by my coffee beans.

The important thing is that this little rig stirred up a lot of discussion and thought at many levels. I tossed out the proof of concept; I want to see what the community comes up with in response.

Don't get me wrong -- I tend to think that its a great device and probably measures what you want to know on a day-to-day basis for those of us that don't pull hundreds of shots a day.

Another vendor that I've used for their fast-response time cooking thermometers is the Thermapen. This is "The" thermometer for the barbecue crowd, and the expensive one is T/C based.

One might be able to tear one of these apart for an $85 probe/meter combination.
http://www.thermoworks.com/products/the ... index.html
(The 0.1 deg. F readout only goes to 200 deg F, unfortunately. If you are comfortable with C, you could use that one.)

They also have panel meters (without sensors) in the $130 range with 1 deg. F accuracy
http://www.thermoworks.com/products/panel_meters/

Jeff wrote:Don't get me wrong -- I tend to think that its a great device and probably measures what you want to know on a day-to-day basis for those of us that don't pull hundreds of shots a day.

Not at all. I do not want folks to get the wrong impression about the device's function and accuracy. I think it works fine for the intended audience and function, however, if you want to make precise measurements this would not be the best option.