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Topic: PID control of roasters and kaffemachines (15 msgs / 330 lines)
1) From: John Abbott
I replaced my triacs with relays. I couldn't always turn off the triac.  =
I'm
sure it had something to do with the control voltage, but I couldn't find=
 it
 The relays haven't failed once.
--

2) From: Chris Schaefer
OK, so all this recent talk both on this list as well as a.c has gotten 
some of my internal brain fire a'stoked.
I work a for a software company that writes and sells programming 
softwares for Porgrammable Logic Controllers.
We ahve a family of PLCs that are considered to be "micros."  So, I'm 
thinking of a good homework assignment, and if it gets off the ground, 
I'll let every know how it goes.
Right now, my Rancilio Silvia is PID'd.  And back when I worked at WB 
on the 'wb' roaster, we had a unit for in-house testing that used some 
mutant between a PID and a PLC for controller the temp on a home 
roaster.  So, you can see where this is headed.  A PLC has many 
outputs, so I could rig up both but I'll probably start with a Poppery 
II.
Our software as a built-in PID function but what I'm thinking is 
actually building time/temp control charts.  *grins*
And if you think you can find PIDs cheap at on-line auctions, you can 
also find cheap, older PLCs.  A _tad_ larger than your block-mounted 
PIDs, however.
l8r,
Gonz
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3) From: Ben Treichel
Chris Schaefer wrote:
<Snip>
Oh, yeah. How much are they? I'm toying with the idea of using an AVR 
micro for the same purpose.
<Snip>
Was thinking the same thing, multiple profiles stored, 20 or 30 set 
points, temp ramped between specified time.
Also logging roast data, for retrieval after the roast (time vs. temp).
<Snip>
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4) From: Gary Zimmerman
Okay, a PLC is a programmable logic controller.
What's a PID and AVR (and any other acronyms that might be thrown around in 
this discussion)?  Also, what's a variac and triac?  (I've read Asimov, so 
I know what a MultiVac is.)
I'm not into electronics except computers, so I'm not familiar with the 
jargon.  I'm not likely to try any of the stuff you folks are discussing, 
but I do find it interesting to read about - I just feel a little lost most 
of the time.  In general.
  :-)
-- garyZ
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5) From: EskWIRED
<Snip>
Oh! Oh! Oh!  I know this one!
A variac is a variable transformer.  It is a big, heavy device with coils of
wire and a knob.  It allows you to vary AC voltage, either up or down.
A triac is a solid state device which is used in a standard light dimmer,
among other places.  In the light dimmer application, it turns the
electricity off 120 times a second, for adjustable slices of time, allowing
you to dim the lights and save electricity.
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6) From: Ben Treichel
Gary Zimmerman wrote:
<Snip>
It is a standard control loop with Proportional, Integral, and 
Differential terms, that are applied to the error (desired vs. actual) 
to the variable to be controlled. (temperature in this case)
<Snip>
AVR 8-Bit RISC
 Atmel's AVR 
microcontrollers have a RISC core running single cycle instructions and 
a well-defined I/O structure that limits the need for external 
components. Internal oscillators, timers, UART, SPI, pull-up resistors, 
pulse width modulation, ADC, analog comparator and watch-dog timers are 
some of the features you will find in AVR devices.http://www.atmel.com/atmel/products/prod23.htmAnd, not asked yet ( ;-) ) an SBC is a single board computer. 
Specifically in this case, all the 'other stuff' that allows an embedded 
micro to do its job, without ant other help.
<Snip>
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7) From: Dan Bollinger
PLCs offer many advantages over simple PIDs.  For instance, you can monitor
heater output and bean environment simultaneously.  You can set internal
timers with temperatures...  Many possibilities.  They are out of reach for
most people and the programming isn't standardized.  :(  I just started
using AutomationDirect's small DL05. If I can't get them working, I might
have to give you a call!  Won't you have to upload a new program for each
profile?
<Snip>
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8) From: Dan Bollinger
<Snip>
And a Fuzzy Logic controller 'learns' from the input's and output's history
and changes the PID values constantly.   For instance, a Fuzzy Logic
thermostat will learn how an oven heats up and will know when to turn off
the heating elements before the desired temperature is reached knowing that
the temperature coasts upward for awhile. Dan
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9) From: Ben Treichel
Dan Bollinger wrote:
<Snip>
Actually a classic example of a fuzzy logic controller is a human acting 
as an automotive cruise control. Look at the speed, are you at your 
"sets speed', Yes, don't do anything. Else, too fast, let up on the gas 
pedal some, too slow, give it some more gas. Its all based upon a little 
more, a little less, or alot more....  Now if you want to make the 
system Neural fuzzy, that's when you are use to your own car, and have a 
pretty good guess as to about how much more etc...
By now we probably have Sir Frederick turning in his books. :-D
<Snip>
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10) From: R.N.Kyle
This is a multi-part message in MIME format.
Go to it. I wish I understood all that you posted. I will be interested =
in the outcome, as I to roast with a PII. my only control now is a 3 way =
switch and thermometer.
Ron Kyle
a coffee roaster from South Carolina
rnkyle

11) From: R.N.Kyle
This is a multi-part message in MIME format.
Thanks Gary I was beginning to think I was the only person feeling a =
little lost. I to like reading and learning.
Ron Kyle
a coffee roaster from South Carolina
rnkyle

12) From: AlChemist John
Sometime around 11:32 9/11/02, EskWIRED typed:
<Snip>
If the rating is acceptable, do you know if there is any problem using a 
triac on a heating coil?
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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13) From: Dan Bollinger
<Snip>
allowing
<Snip>
John,  No problem whatsoever.  Both lights and heaters are resistant
devices.  Problems will ocurr with inductance devices like motors and
flourescent lights.  There are commercial light dimmers that fit in a
standard wall box rated for 600W, 1000W, 1500W and 2000W.  Made by Nova,
Centurion and Athena.  Graingers has them all.  Dan
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14) From: EskWIRED
<Snip>
I don't really know for sure, but since a light bulb is in essence a heating
coil, my guess is that you'll be OK.
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15) From: dewardh
John:
<Snip>
triac on a heating coil?
None at all . . . triacs like simple resistive loads without inductive spikes 
or skewed power factor.  Their "issue" is that they are not pure switches . . . 
they have a finite "on" resistance, so they dissipate power internally in 
proportion to the load current.  With a 10 Amp load the triac will dissipate 
(typically) about 15 Watts, and will require sufficient heat sink to keep its 
temperature down.  That's why ordinary dimmers (even the fancy "motor 
controllers" with higher ratings) fail when used on heaters, especially when 
the heater is run near to full on.  Ordinary wall dimmers are rated at 5 Amp 
max, and will pop in seconds with a 10 Amp load.  The "10 Amp rated" motor 
controllers depend on the fact that drills and routers see full load only 
momentarily on startup (or when they hit a nail ) . . . at 10 Amp continuous 
they too will fail, although not as fast as a light dimmer.
A properly rated triac, with adequate heat sink, will work fine with a heating 
coil load.
Deward
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