Hey all,

I'm about to buy some phidget robotics computer I/O gear and use a graphical programming "language" by dsp robotics to try to gain some more control over my roasts. Basically, i'm tired of sitting outside with my variac and want to make my computer do my job. Honestly, I'm just not that good, either. I can't control my roasts to the point where I am consistently isolating each variable at a time.

Anyway I'm posting here because I'm not that skilled with any of this and was wondering if someone thought about going this route and then gave up for some reason or another. Parts are going to cost me about $150. Designing the program will probably take a day as well. (the "language" is basically a graphical front end to C++ or something - graphics to represent blocks of code which I can connect to make a program).

Anyone have some PID parameters for bean temp? I know people usually profile off ET, but I was gonna try BT first.

The PID parameters depend on the individual system of heat/airflow/construction. You'll have to tune the PID to match your system - a pain, to be sure, but once it's done, you'll be glad you went this route.

'course you could just plop in an off-the-shelf PID controller...

I was under the impression that an off-the-shelf PID controller could hold a system at a present temp (i.e. y=420) or ramp to a temp (i.e y=a*x + b) but couldn't do anything more complex than that. Is that correct? Or can I define a complex profile of 4 or five segments for an off the shelf PID?

Hi.

Yes, you can buy PIDs with programmable soak/ramp segments. The Fuji PXR has up to 8 segments. The Fuji PXG has up to 16 segments. But usually there are other variables like fan, dumpers, etc, and drum temperature alone is not enough to cut through the cheese.

Controlling the BT profile of roaster directly with a PID does not work for drum roasters. It may work for air roasters. It would be like controlling the inside temperature a leg of lamb using your kitchen oven setting. You can directly control the outside temperature but not the inside. With a PID it would create huge overshoots/undershoots.

Cheers

I use an Omron E5CK-T (the -T model has four programs of 8 steps each) with a BT probe on my iRoast. Works great at 150-160g (depending on chaffiness of bean).

You can sometimes score a programmable PID for a good price on eBay if you look for them.