Note: This was first posted inside another thread, but I realise it will have more visibility as a separate thread.
I have to admit that the urge to buy thermocouples/data logger has taken me, as I realise that what is needed to use temperature as a roast progress indicator is really the bean temperature (BT). Else, I can only use indirect indicators: environemental temp (ET), color, sound, smell, smoke and past experience as guidelines to know where I am in the roasting process and when to end it.Choosing a datalogger
There a a lot of different choices available, with different levels of functionality, user friendliness, construction quality. Note: As I'm in Canada, I've looked at Canadian prices, which may differ from US prices. All prices cited are in CAD.
All models referenced here offer: the same precision (0.3°C), 2 channels, wide support of thermocouple (TC) types, and max sampling frequency of 1 per sec.
- 2 channels, to record both BT and ET.
- Ability to record data for the duration of a roast (sufficient memory).
- Ability to datalog in real-time to a connected PC, to eventually use software such as Artisan
during the roast.
- Good quality/functionality - price ratio.Fluke 54 IIActive123.com
$548 +$170 for FlukeView software + IR/USB cable + TC probes
(+) Good build quality.
(+) Easy to use.
(-) No real-time logging to computer (can only transfer pre-recorded data).
(-) Memory limited to 499 data points.
(-) 2 channels must use the same thermocouple (TC) type.
(-) Pricey (especially with the software).Omega HH506RA or Extech 421509Omega model at omega.ca
$169Extech model at active123.com
+ $30 for serial to USB cable/adaptor & basic software + TC probes
(+) 2 channels, each can accommodate different TC types.
(+) Allow real-time logging to computer (although data points maybe dropped by serial link).
(~) 1,024 data point memory.
(-) Less easy to use but can be managed.
(-) Lesser quality compared to Fluke.Omega HH806, models W, AU or AWomega.ca
- W (Wireless, no USB) version : $199. 1,024 data points memory. Batt. only. 900MHz Wireless (require USB dongle).
- AU (USB) version : $210. 16,000 data points memory. AC adaptor avail. USB port.
- AW (USB + wireless) : $315. 16,000 data points memory. AC adaptor avail. USB port. 900MHz Wireless (require USB dongle).
+ $22 for USB cable/software or $40 for optional wireless receiver/software + $10 for optional AC adaptor
(+) Large memory (AU and AW models).
(+) AC adaptor avail. (AU and AW models).
(+) Integrated USB port.
(+) Wireless option (W and AW models), which would allow me to use software such as Artisan on my desktop computer while the roaster/datalogger is kept under the range hood.
(+) Still cheaper than a Fluke, even with the premium for the AW model.
(-) Lesser quality compared to Fluke.
(-) W and AW not compatible yet with Artisan but the dev. team is open
. I would expect at least the AW to work when plugged in via USB. If the wireless works too; great.Data logger prefence for...
The Omega HH806AW or the HH806AU (w/ | w/o wireless).
I've also considered the Thermoworks TW-USB-TC-LCD
($99), but it only supports one TC.Setting up the TC probes in the Hottop
Basically, two options:
A. through the loading chute cover (Randy Glass' page
(+) Temporary. The roaster can be brought back to its original state by buying a new chute cover.
(+) With Randy Glass' work, I know exactly where to drill and how.
(-) Looks like an after-thought. Have to manipulate the whole rig to load beans.
B. through a drilled hole at the back end of the roasting chamber
(+) Permanent. A more professional solution.
(-) Need to be sure where to drill holes for BT probe to keep it in contact with moving beans.
(-) Need to fix the probes in some way to keep them from moving back and forth.
I still need to decide which I will go with...Q.
Comments? Suggestions?Choosing the thermocouplesOmega.ca
has some well written documentation on thermocouples (how they work, the different types, etc.).TC type
Most seem to use K type TCs, although T type are more accurate. When I use the Omega Probe Configurator
, K and T type probes are the same price.
I will then order T types probes, as I see no reason not to do so.Q.
Have I overlooked something?TC build
I will go with a rugged transition joint with stainless steel overbraid wire, stainless steel sheath, 6" length (to be confirmed if I chose to install them through the back wall of the roaster), 1/8" diameter.TC junction type
Three choices here:
A. Exposed. Very fast response time. The TC junction is naked and unprotected. Not adequate for my use.
B. Grounded. Fast response time. The TC wires are physically attached to the inside wall of the probe. Probe is subject to electrical ground loop, creating noise on the line, affecting the temperature reading.
C. Ungrounded. Slower response time. The TC junction is detached from the probe wall. Offers electrical isolation. Longer lifetime.Q.
As the probe would be in contact with the roaster frame (which will be grounded to the electrical outlet, while the data logger will not...?), would the ground loop issue affect the temperature reading or not?
Regarding response time, Omega provides a comparison table (in air)
but it only seem to compare exposed to grounded probes. Another chart
compares exposed, grounded and ungrounded probes response time in water. According to this table, a 1/8" probe would result in 350ms response time (to reach 63% of the temperature change) for a grounded probe, compared to 550ms for an ungrounded probe. To reach near to 100% of the temperature change, this needs to be multiplied by 5, hence 1,75s vs 2,75s. Again, this is in water. In air, response time for the same grounded probe seem to be 10s (or 50s for 100%) (from the first chart)?Q.
So... what is best: grounded or ungrounded?
Last but not least, I need to see what kind of probe I need to buy (a third one) to replace our always broken cheap electronic cooking meat thermometers (we have gone through 5 of them in the last few years)! K or T type... grounded or ungrounded? Q.
Any comments or suggestions?