okmed wrote:

Barry, I believe Turtle used the OEM thermocouples ( see here http://forum.homeroasters.org/forum/viewthread.php?thread_id=2999&rowstart=80#post_51080 ). They are $40.00 from Hottop so that is a bit more than the $21.50 I paid for the Omega's. It definitely makes it easy to mount though. You might want to check with Randy from Hottop on the length of the leads to make sure they are long enough, or since you have the 2K model you can measure the lead for yourself.

GreenBean wrote:

I believe that JimG has recently changed PCB fabricator. From the latest update on his website I expect he will be back in production soon. ...

BarryR wrote:

If I get something like the Omega probe with an Inconel collar, would that fit directly in a compression fitting or do I still need to epoxy it?

okmed wrote:

I didn't use a back nut, I just tapped threads into the back plate. The silicone tube sleeve provides both electrical and thermal insulation. I needed the electrical insulation because my probes were grounded. I chose grounded probes for quicker temperature response. Using 1/4" compression fitting and 1/4" silicone tubing captures the 1/8" probes nicely.

BarryR wrote:

[quote]okmed wrote:


OK. I think I almost got it. A few more questions though:
You said you used 1/8 inch NPT on the compression side. How does a 1/8" probe fit inside 1/4" tubing with a ferrule (or am I misunderstanding something here).


Yes welcome to the wonderful world of pipe thread sizes. The opening in the 1/8" NPT fitting has about 1/16" clearance around the 1/8" probe. Go to Home Depot with a ruler and measure up the fittings for yourself so you have a clear understanding.


Also, what tubing and ferrule do I need (just want to get them ahead of time if I can't source them locally).


As I said in my previous post, I used 1/4" OD silicone tubing which fits a 1/4" compression fitting and used nylon furrules instead of the brass ones that come with the compression fitting. 1/8" probes will fit inside the 1/4" silicone tubing with a little dish soap to help it slide. You actually only need about 5/8" to 3/4" of silicone tube to fit inside the compression fitting to act as thermal and electrical insulator.


If I get the fiberglass covered probe doesn't that mean I don't have to shove the wires through the silicone?


I have not seen this fiberglass covered probe so I can't answer that.


Do you find that the backing plate is thick enough to sustain the threads and the fittings?


So far the 1/8" NPT is holding fine in the backing plate.


Finally (maybe): I don't have anything to grind the fittings. Is this necessary or does it just reduce heat sink mass?


You can use a hacksaw and a file or not. If you don't shorten the thread then don't run the tapered tap through as far. You don't want too much thread protruding into the roaster. Also, I think 1-1/2" probe won't be long enough. You want the compression furrule to be around the tube and the probe.


Thanks!

GreenBean wrote:
3. My view is that 3 mm diameter probes offer the best compromise of smooth output, speed of response and robustness (of the sheath and thermocouple wires). 1/16? thermocouples will work but you should expect less smooth temperature and RoR curves and may have issues with breaking thermocouple wires.

GreenBean wrote:

I see that you have started a thread on another coffee forum discussing this same subject i.e. advice on installation of thermocouples in your Hottop. It is difficult to follow your current thoughts on what you propose to do across the two threads. There are many different approaches possible and you have received good advice from a number of contributors. The solution proposed by okmed looks good to me provided nylon ferrules are only used on the cold side of the fitting. My views on what I perceive to be your current proposal are:

1. There is no substitute for dismantling and measuring your Hottop with your proposed solution in mind. I believe Hottop have made changes to the design of key elements such as the drum. Measuring your own Hottop is the only way to be certain that your solution will fit.

2. Choose the thermocouple length to allow maximum safe protrusion into the roast chamber. This will provide the most accurate readings. The drum drive motor can be disconnected to allow the insertion or removal of the thermocouple.

3. My view is that 3 mm diameter probes offer the best compromise of smooth output, speed of response and robustness (of the sheath and thermocouple wires). 1/16? thermocouples will work but you should expect less smooth temperature and RoR curves and may have issues with breaking thermocouple wires.

4. Fibreglass insulation provides good thermal insulation to the thermocouple wires but is not ideal to insulate them electrically from any mains connections within the roaster. To ensure a safe installation you should route fibreglass insulated thermocouple leads through suitable silicone sleeving/tubing.

5. The rear wall of the Hottop is too thin to provide a robust threaded connection to the fitting although okmed reports good results so far. The connection may well fail after a time. In this case you would still have the option to fix it with J B Weld.

You have asked if RoastLogger will graph the fan and heater settings. I have deliberately made the decision not to chart this information as I believe it encourages users to think, and attempt to control their roaster, based on elapsed roast time. Elapsed roast time is a poor indicator of roast stage and attempting to control a roast based on this produces poor results. I have covered my views on this in several posts on other coffee forums. In summary, RoastLogger allows you to control the roast by making changes to the heater and fan based on bean temperature. This produces much better control of a roast and more consistent results in the cup. RoastLogger provides a simple set of tables that allow you to script the changes in settings. These changes are applied exactly as scripted in each roast and RoastLogger indicates when each change is applied. Charting this would not provide any additional useful information.

BarryR wrote:
4) Isn't fiberglass an electrical insulator?

BarryR wrote:
...The XCIB is 6.4mm diameter with an exposed tip, so I imagine this would combine the benefits of ungrounded (not needing grounding) with the rapid response time that the exposed tip provides.

BarryR wrote:...Has anyone mounted the XCIB type without the epoxy? If so, which thermocouple or other method was used....

BarryR wrote:...I recall on poster epoxying a sleeve but then holding the probe itself in place with basically friction fitting in a silicone (or such) sleeve. Wouldn't this tend to shift?...

BarryR wrote:...I believe the XCIB is stated to be very durable but for the BT probe, wouldn't the beans constantly banging into the exposed tip put it at risk for breaking?