Posted Fri Jan 15, 2010, 11:15am Subject: Tenma 72-7712 Thermometer
Danscoffee phase suggested this data logger in another thread found here: "Temperature Data Collection ...??" as an answer to Jerry K's questions on data logging device that would store temperature history and not have to be hooked up to a computer while doing it. Dan posted this info: I got it from MCM Click Here (mcmelectronics.com) for $49.95 on sale (regular $85.49). MCM is one of those places that never shows sale prices on their website, you need a catalog code (try 18SC8 until 1/30/10). These units can still be purchased for a few more days at the sale price so I wanted to bring this product and these comments up before the sale ended.
Jerry then bought one and has had a pretty good experience with the unit. I have been picking Jerry's brain about the unit often and purchased one as well. I'll let Jerry speak for his own experiences about the unit .
My own take on the Tenma is that it is giving me information that I just didn't have before. I've logged my roasts recently but was unhappy with the level of precision in my data collection. I tried to make an entry once a minute of not only bean mass temp but also environmental temp, T1 and T2. I bought a dual input thermocouple from GainExpress on EBay and I liked the unit. I just had to manually watch the beans, the clock and write things down with pen and paper and sometimes I would glance down and I missed my mark by a few seconds. Trying to capture both temps T1 and T2 on the minute, was a frustrating experience.
The Tenma unit auto logs one channel, in my case I choose bean mass. I can monitor T2 or environmental temps but I no longer log them. I really like the nice graph it produces and I can see things that I normally wouldn't notice.
My very first roast which I plotted I noticed the heat transfer to the beans was very linear. It was actually too linear for my taste. The next roast that I logged I tried to stretch out the time from T1 to T2 enclosed are two charts. I havenít converted the intervals two time, so each time point that is recorded equals 11 seconds.
If you are looking for a way to gather better info about your roasts this might be a great inexpensive way to do just that. It's still on sale until the end of the month.
Jerry is better with Excel than I and he manipulates the data. I hope that he will jump in on this thread.
Didn't know how to add both charts at the same time. Note on this second chart there is one data point that is false. You can see the sharp drop. This is the raw chart but in Excel you could drop that data point before you plotted your information. Notice that I preheated the chamber, then I dumped the beans then I ramped up to first crack and tappered off to second crack in this latest roast profile.
Posted Sat Jan 16, 2010, 6:05am Subject: Re: Tenma 72-7712 Thermometer
The TENMA 72-7712 is a Thermocouple Reader, for Type K, J, T and E type thermocouples.
It is similar in appearance to other readers that you can buy on eBay (from China). This one is probably (?) made in China as well, but it is sold and guaranteed by MCM Electronics, click here.
While it has the features of the other low-cost readers, such as reading from 2 thermocouples: T1 or T2 or T1-T2 it does more things that make it ideal for coffee roasting:
It lets you correct each input for error. Thermocouples are usually =/- 3 degrees F, I have been able to readjust mine in the setup procedure to +/- 1 degree.
If you have a laptop computer you can collect data 'live' into your hard drive, any number of points and any interval. If you don't have a laptop you can collect 100 data points into internal memory at any convenient interval and download them later. You get them in MS Excel format, *.xls, so you can massage them later.
The readout of temperature you watch while roasting has a resolution of 0.1 degrees F. So if you are trying to slow down a roast, but don't want it to stall, and you hope temp is rising (say) 1F a minute, it is nice to see (say) 400.1, 400.2, 400.3 ...etc., going up every 10 seconds.
While the price of $85.49 is a bargain, compared to other instruments which do data-logging, they go on sale, from time to time. Mine came in at around $49.95 plus reasonable shipping charges and the discount code: 18SC8 is supposed to be good until January 30.
Actually, they quoted shipping charges of $11.99 for US delivery and $13.99 for Canada (where I live). When the box arrived, the stamp (actual postage) was $22.95. My VISA was debited only $11.99. I don't know who handles their shipping, but I like him ...!!
The instrument has worked perfectly. The manual is well written and useful. there is a separate manual for the software on a CD and it is not well-written and not useful. However, it is a tiny program and I was able to hack my way through it without much trouble.
Posted Sat Jan 16, 2010, 6:58am Subject: Re: Tenma 72-7712 Thermometer
Jerry - What computer os is supported for computer downloading? Win xp, vista or older? I mainly use a Mac, but do have a netbook I could use. Does it store both thermocouple readings when not connected? Does the unit transfer both thermocouple readings to the computer live, or just one?
I am using WinXP myself. I have only tried 'computer downloading' once and got 1000 points in about 2 minutes before I figured out how to turn it off. So if that's what you want to do, there will be a bit of experimentation on your part. Also, the software stores in .xls format for an old version of Excel, maybe Win95 era. But it's OK; you just re-store the file in modern .xls format.
You can store (either way) T1, T2 or (T1-T2). Only 1 reading. While it is storing readings the instrument scan rate increases x 5 so the readout is very busy. What you see: the large line on the top shows the current temperature and the small line on the bottom shows the point number and the value stored.
I can add this about it (not that you asked) ...the interface, that is, the buttons and the readout, are well thought out and easy to use. For example, when you push the button to collect data ...it does not start ...until you push the enter button ...and you stop the collection process using the enter button. So if you want to pause it in the middle ...and restart it 20 seconds later, you can do so.
Posted Sat Jan 16, 2010, 9:16am Subject: Re: Tenma 72-7712 Thermometer
Joe, I have had many eBay transctions with a store in China called Procon-Products click here. The have fast shipping, usually under 2 weeks.
The one I use is sheathed in stainless-steel, immersion length is 100mm, cable length is 2 meters, with a yellow Type K plug, braided SS sheath over the wire and a threaded connection and matching nut. I think it is rated for 1000F, suitable for kilns and roasters.
It's a nice piece of work and costs $8.00 + $3.00 for shipping and handling.
I presently have 3 of them.
If I bought them from an instrument vendor in Canada, they would cost at least $100 each ...!!
DansCoffeePhase Senior Member Joined: 2 Dec 2009 Posts: 28 Location: OK Expertise: I love coffee
Espresso: Gaggia mod (PID+OPV+3way) Grinder: Cunill Brasil Roaster: TC/CO
Posted Sat Jan 16, 2010, 10:20am Subject: Re: Tenma 72-7712 Thermometer
I was motivated to get a temp logger after accidentally producing a great roast with flavors I'd never gotten before (very nutty with vanilla & spice), and not being able to duplicate it.
It's been a lot of fun to use and enabled me to do experimental roasts, like in the graph below, to learn the limits of controlling my roaster manually with a router speed control. It's so much easier seeing on a graph the temp rise rate at different power levels, and how steady I can hold the temperature at different settings.
For this experiment (300g Yirga Cheffe), I was trying to slow and extend 1C as long as possible, and get the longest gap between 1C and 2C without baking. I started ramping power down before 1C (normally 1C begins at 11min). Tastes a lot better than I expected: the typical Yirg blueberry flavors have become a very intense Merlot wine flavor and aroma.
I'm glad you guys like the Tenma, I really like mine.
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