Posted Sat Dec 1, 2007, 12:04am Subject: If you temp surf, use a thermometer.
Imagine how a PID controller would work without a temperature sensor on the boiler.... How can you expect to control your brew temp if you don't know the temperature of the boiler? Boiler, heater, cold water are too complex to be a predictable model based on when heaters turn on and off. Add a cycle to steam and back to brew? Now what do you do? It's just plain simple obvious that you need to know the boiler temperature to know when to pull the shot.
Posted Sat Dec 1, 2007, 7:26am Subject: Re: If you temp surf, use a thermometer.
As a complete noob, whithout an espresso machine, I ask you: What is the theory of having a thermometer stuck to the side of the boiler if the thermostat that the machine itself uses functions correctly. If you measure once the temperature to ensure that the temp of the water coming out of the group matches what it's supposed to be, then is there a need do continue surfing? I am really asking if your idea is to install a permanent thermometer, or is it to install a temporary one to calibrate/check the factory-installed thermostat? Is it because you (me) doesn't know what temp the water is when you want to pull the second shot after a steam mode, or is it because most machines don't get hot enough and you have to hit the steam mode just to get it up to temp period?
|| http://thoughtcompile.blogspot.com/ | + | It takes an average of 42 beans to make a shot. Douglas Adams wrote in the Hitch Hiker's Guide to the Galaxy, that 42 is the meaning of life...coincidence?
Posted Sat Dec 1, 2007, 9:42am Subject: Re: If you temp surf, use a thermometer.
It is for the reasons you mention.
But mostly, I think, the thermometer would assist in tracking the temperature cycle allowed by a mechanical thermostat. These thermostats have an intentional "deadband" (more properly, hysteresis). When the temperature is within the deadband on either side of the setpoint, the thermostat will not switch. Only after the temperature has passed by the setpoint, and also left the deadband, will it switch.
In addition to the deadband, there are significant lags in the system. After the thermostat turns the heater off, the boiler temperature will still continue to rise several degrees. After the heater turns back on, the temperature continues to drop for a few more seconds.
The result of all this is a repeating cycle of maximum and minimum temperatures. For example, on a Silvia, the range from maximum temperature to minimum temperature is at least 40F. I think the Venus is similar.
So with a perfectly functioning mechanical thermostat of the type used on most single boiler espresso machines, you cannot really know the boiler temperature with certainty at any time (except that it lies within this 40F range).
A thermometer allows you to time your shot, or "surf" the 40F temperature curve.
Posted Sat Dec 1, 2007, 1:37pm Subject: Re: If you temp surf, use a thermometer.
It makes common sense that if you want to know or control temperature, a thermometer is a handy thing to have. It is really handy when you are trying to control brew temperature within a few degrees. It is the only way you can really characterize the thermal behavior of your machine.
I put a thermometer on the Venus boiler top in the first week I had it. After using one on my previous Gaggia, I was completely lost without it on the Venus. After a couple months of observing, testing, pulling shots and steaming, I'm finally getting a routine that works to efficiently cycle the boiler and park it where it's needed to pull the next shot.
By using the styrofoam cup to measure brew water temp and comparing with the boiler temp, I determined that to get 200F brew I needed to be 8-10F above that (and stable) at the boiler top. ( After you are this close it doesn't matter to be exact: you go by taste, raising and lowering the temp 2 degrees or so and see what works best for your beans)
One thing I noticed on the Venus, there are 2 different 'cycles' of heater: if the machine sits idle it will cycle between 194 to 206F (very repeatable) over about 7.5 minutes and the heater will cycle for 14 seconds to raise the temp from 194 to 206. Now if you run the pump and put about 4-5 oz of cold water in the boiler, the temps will drop to 185 or so and the heater will cycle for much longer..... and it will overshoot to about 234F. In both cases, the peak/stable max temp is reached 35-45 seconds after the heater is shut off.
So, now we can start to answer important questions about how to control temperature, becoming the 'intelligent controller' that is lacking in your $14 snap action thermostat. You can relieve the thermostat of it's poor job performance and manually take over.
If the boiler is at 250F and you just finished steaming milk, how long should you turn on the pump to bring the boiler back to brew temp as quickly as possible?
If the boiler temp is at 203F and you want it to be at 210F, how long should you turn on the heater?
If you are only pulling shots, not steaming milk, how long should the heater be turned on between shots to maintain the boiler at your desired temperature?
These questions and more can all be answered after you get a reliable reading of your boiler temperature. Controlling temperature without a thermometer is flying blind without instrumentation.
I tend to assume here that the DIY mods are taken on by someone comfortable taking things apart and fixing, etc. So I would caution anyone not familiar to be extremely careful when making any modifications: For safety and reliability of your machine. There are live 120volt (some exposed) connectors on the heater, etc. Always unplug the unit and watch out where you route wires, etc.
For the styrofoam cup/ thermometer test, a quick search here will bring up your answer. In the last couple weeks there was this thread on the subject:
I don't think you need to get too carried away with absolute accuracy here: the point is to get you within a few degrees. From there you can dial in by taste. (Later on you can do a project on intra-shot temp stability.)
For the boiler probe, the short answer is ' use sound engineering practice'. Ideally you want the probe in direct contact with the water delivered to the puck. I settle for good thermal contact to the boiler (in my case on top of the boiler with thermal paste to help conduct, and insulated on top). I also insulated the boiler. This improves temp stability. I looked for a nice simple thermometer package: small temp display to put on the front of the machine, probe, wire. I never found anything that looked good so I used what I had on hand:
fancy_pilot Senior Member Joined: 10 Oct 2007 Posts: 81 Location: Iowa Expertise: I love coffee
Espresso: Saeco Classico Grinder: Gaggia MDF
Posted Fri Jan 18, 2008, 11:46am Subject: Re: If you temp surf, use a thermometer.
I used a TruTemp from Taylor - #3516 that I picked up from the kitchen section of Target. http://www.taylorusa.com/consumer/thermo/kitchenth.html , but any thermometer with a range up to 250-270F would work.
Most versatile is a digital thermocouple thermometer. Inexpensive ones, that read type K probes only, can be purchased for under $30 (including sensor). For instance, Sweet Maria's has one with their roasting accessories. I have seen this same unit on other web sites, but cannot recall those URL's at the moment.
There are even several inexpensive digital multimeters that can read K thermocouples. I probably wouldn't go this route, however, because DMM's usually do not use a standard thermocouple connector. This can limit your choice of sensor probes, or force you to use a special adaptor.
Professional digital thermometers from Fluke (series 50) can cost over $200, but are more accurate, have faster response times, and can read a variety of different kinds of thermocouples (T, K, J, etc).
For mounting to the boiler, you can probably get by with the bead probe that typically comes with the thermometer. Just clamp the bead under a screw head or bracket. A little bit of heat sink grease is good if you have it, but not a fatal flaw if not. It is safe to flatten the bead with a pair of smooth jaw pliers to make it easier to mount.
A little better option for the boiler is a washer type thermocouple. Omega Engineering is a popular, and usually good, source for these. Item no. WTK-6-36-TT would be a good option for a Silvia - click here. Be sure and order the appropriate connector as well (SMPW-CC-K-M, for instance).
The inexpensive thermometers generally can't be expected to give temperatures any closer than +/- 2F, and the response to quickly changing temps is usually slow. But you might still want to use it with an "over the lip" thermocouple to measure brew temperature (click here for Kristi's excellent post). A simple, fine wire bead probe will do the trick. Unfortunately, Omega seems to require purchasing these in lots of 5. So you would probably be better off buying some wire and making your own (TT-K-30-25).
The advantage of going the thermocouple thermometer route is the ability to use a wide variety of different probes with the same thermometer. Type K probes in all kinds of configurations get listed on eBay frequently.
Cooking thermometers usually must be used only with the probe that they come with, so are a little less adaptable. (Exceptions are some models of the ThermaPen).
bigstu44 Senior Member Joined: 16 Jan 2008 Posts: 41 Location: UK Expertise: I love coffee
Espresso: Isomac Zaffiro Grinder: Mazzer Super Jolly
Posted Sun Jan 20, 2008, 5:31pm Subject: Re: If you temp surf, use a thermometer.
I have a Silvia and Jim very kindly directed me to this discussion. I'm very interested indeed in doing this mod. I have a couple of questions though, for Frost:
1) You mention switching the heater on/off. Has your machine got a switch for directly controlling the heater? Or did you mod it? Or do you just switch the entire unit on or off? The Silvia has no way of directly controlling the heater-it's on/off only on the command of the thermostat (the only way of indirectly controlling the thermostat is, of course, running the pump)
2) You also mention waiting until the temp is stable to pull a shot. Makes perfect sense. But how is this stability achieved? Surely, heater on or off, the temp is always going to be in a state of upward or downard movement? Or does the water cool a lot slower than it heats, giving more stability in the cooling part of the cycle?
Posted Mon Jan 21, 2008, 12:47pm Subject: Re: If you temp surf, use a thermometer.
Welcome to CoffeeGeek Stuart. To answer your questions:
I did not modify the heater controls on my Isomac Venus. I use the machine on/off switch to manually control the heater. Setting the 'Steam' switch on will enable the heater up to steam temps so I can over-ride the brew thermostat completely.
(For warmup and Idle time on the machine, I use the thermostat to maintain machine temp)
"stable temp" should be more carefully worded as "most stable temp". On my Venus (I also insulated the boiler) There is a time period of at least a full minute where the effects of heat gained from the heater peak and before the temp starts to significantly drop. The 'peak' of the temperature curve: about 35 seconds to 1 minute 35 seconds after the heater cycle completes on my Venus) This is a comfortable easy amount of time to get the shot together.
The cooling part of the boiler cycle is much slower/longer than the heating. It would still give a good window to pull the shot.
A little more specifics on my temp surf routine as it is now: I steam milk for Capp's so I cycle the machine to/from steam for each double. After steaming, the boiler is 250-255F. At this point I run the pump for 20 seconds to fill and cool the boiler. This draws about 3 oz in a cup to warm it and the boiler will drop down to about 185-190. ( need to cool that grouphead down!) Then I turn on the heater for 20 seconds. 35-45 seconds later the boiler is at 208-210F and ready for the next shot. Also, I turn on the heater 8-12 seconds before I draw the shot (when I am ready to lock in) and the heater stays on through the shot pull and milk steaming. This will improve the temp stability during the shot!
Of note on the Silvia with offset grouphead and larger temp differences from top of boiler to brew: It occurs to me that perhaps you could use the 'cooling flush' after steaming milk to put the grouphead at the proper brew temp. It is clear to me that the offset grouphead complicates temperature control on the Silvia and the issue is worth some special attention ( can insulation help here as well?)
Good luck with your testing and experiments and please update here on your findings. I'm sure others will be interested as well!
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