I decided to add more insulation to my roaster, because of this thread.

I have a two soup can high chimney. Before, I had one layer of 1/2" melamine foam on the first can only, with the 2nd can just kind of sitting on top of the first.

I cut a bigger piece of foam and wrapped it twice around both cans.

After doing this, I have a larger difference between BT and ET. Before, it was around 30 degrees, now it is around 100 degrees.

Any reason why the delta temp would get bigger with more insulation?

Randy

You should be able to roast at the same speed with a smaller ET-BT delta once you've insulated. How are you measuring?

For ET, I drilled a hole in the heater chamber, in between to of the slots. I use a bead type K thermocouple, which is between two slots, bent to be just slightly inside the roast chamber. This thermocouple is connected to my PID

For BT, I drilled a hole in the body of the popper, angled down. Using a probe type K thermocouple, tip is about 1 inch from the bottom of the roast chamber, missed the center by about 1/2 inch. The roast I did a couple days ago, I had pulled the probe up a little, so it was centered, and probably 1/2 inch higher, and results were basically the same, for difference between bt and et.

The BT thermocouple is connected to a meter with a USB output. I take the data from both thermocouples, and put them in excel to create the graphs I have been showing. I match the falling edge of turning the heat off, to sync the two thermocouples.

I have had the thermocouples like this, roasting from ET for my last 4 or 5 roasts, and roasted from BT before that, with the same thermocouples, and placement. The only thing I changed in the roast I did today was the added insulation, the roast I did a few days ago had added insulation, but also I had pulled up the BT thermocouple.

I am going to roast again in a couple days, I can go back to the original insulation in a few minutes, so I will try that, and see how BT and ET differ.

Randy

Aha! I think you have the sensors in the wrong spots. The bean temp is best measured over the beans, near the top of the chamber, since the air leaving the beans is closest to their temperature (think of a heat exchange process). The ET on the P1 is best measured directly underneath, at the center of the roasting chamber, so the air hots it just before entering. The actual temperatures you read at this spot can vary, from the high 400s to the low 500s depending precisely on the sensor position, but providing the sensor is fixed, it will be very consistent.

Hi Jim
Off topic, when do you sleep? Aren't you in Chicago? So, it would have been almost 4am when you posted this?

Sorry, back on topic.
A couple sensor location questions then.

For ET, in my "Cheap PID" thread, you offered the following advice
"ET for an airroaster is where the heated air first contacts the bean. "
Thats what I tried to do, so I have the thermocouple installed so the tip is where the hot air hits the beans, or as close as I could get to that. I am really not sure where you put your ET sensor in your P1. Is it in the bottom, middle of the roast chamber, where the little bump is? Or, is it actually underneath the roast chamber, and not in the chamber at all? That would put it right above the fan, if I remember correctly.

For BT, then I should move the thermocouple to the top of my Pumper, about at the base of where my soup can chimney starts?

Thanks
Randy

ET where the air enters, BT where it exits. If your ET sensor is in the slot where the air enters, it's OK, if it is in any way in contact with the inside of the chamber, it should be moved. Your BT sensor should be above the beans at the end of the roast. There is nothing complicated about a P1. It's a pipe, the hot air enters the bottom and the less hot air exits the top, the beans are in the middle, getting heated.

I was working late

Got it, thanks.
The ET probe is in the air, not touching anything, so I think it is OK.
I will try to take a pic tonight.

BT gets moved up.

Randy

Probably the BT probe was getting a direct blast from the inlet. Hope moving it up does the trick

I had not roasted for a little while, and the last roast I did, the data came out funny, so I did not post it.

Here is the data from a roast I did tonight.


I have moved my bt probe to the top of my popper, so it is around the top of the beans when the fan is on.

This is with the heavily insulated configuration.

The 2nd hump in the yellow chart is when I slowed the fan down.

Next roast will be with less insulation, so I can compare again.

Looks like the sensors are in the right spots. Are the roasts manually controlled or on the PID?