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'[PIC]:How do I control Temperature using a PIC ?'
2002\04\15@112611 by Coco Caracola

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Hi: I4m working in my final thesis about a temperature process control. The
point is that I need help about controlling a resistance based heater using
a PIC to get an oven heated from one temperature to another..... Can anybody
help me ?

Cuanto mas se sabe, menos se asegura.

      Carlos E. Mangiarotti

     Departamento Ticnico

Ciudad Internet Suc. Rosario

      Tel: 0341-4243770

<http://www.ciudad.com.ar/>

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2002\04\15@114136 by 1?B?c2FtbyBiZW5lZGnoaeg=?=

Hi!

What temperature range are you talking about? Regards, Samo

-----Original Message-----
From: pic microcontroller discussion list [.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On
Behalf Of Coco Caracola
Sent: Monday, April 15, 2002 5:15 PM
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: [PIC]:How do I control Temperature using a PIC ?


Hi: I4m working in my final thesis about a temperature process control. The
point is that I need help about controlling a resistance based heater using
a PIC to get an oven heated from one temperature to another..... Can anybody
help me ?

Cuanto mas se sabe, menos se asegura.

      Carlos E. Mangiarotti

     Departamento Ticnico

Ciudad Internet Suc. Rosario

      Tel: 0341-4243770

<http://www.ciudad.com.ar/>

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2002\04\15@114938 by Douglas Butler

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Are you looking for help with hardware or software?

Sherpa Doug

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2002\04\15@115942 by Coco Caracola

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Hi !!!
Between 20 and 50 : C ....
Wait for your answer ... :)
Bye.

-----Mensaje original-----
De: pic microcontroller discussion list
[spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU]En nombre de samo benedihih
Enviado el: Lunes, 15 de Abril de 2002 12:41
Para: TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU
Asunto: Re: [PIC]:How do I control Temperature using a PIC ?


Hi!

What temperature range are you talking about? Regards, Samo

{Original Message removed}

2002\04\15@120355 by Coco Caracola

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Software ...
I have the measurement done by an IC that gives a proportional voltage to de
temperature it senses. This voltage is A/D converted and y need to follow
some temperature values. In fact I need chocolate to reach 44 o C as quickly
as i can .... The point is not to pass this temperture border ... Can you
help me ? I would appreciate.
Bye !

-----Mensaje original-----
De: pic microcontroller discussion list
[RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU]En nombre de Douglas Butler
Enviado el: Lunes, 15 de Abril de 2002 12:42
Para: PICLISTEraseMEspam.....MITVMA.MIT.EDU
Asunto: Re: [PIC]:How do I control Temperature using a PIC ?


Are you looking for help with hardware or software?

Sherpa Doug

> {Original Message removed}

2002\04\15@140223 by Herbert Graf

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I'm not quite sure where you exactly need help but I'll make a few
recommendations as to how I would go about it. First, I would choose the
16F628 PIC, it has an intenal RC OSC which saves some complexity and is
programmer pin compatible with the 16F84. For temperature sensing I would
use the National Semiconductor LM75 (or a relative of it if you need more
accuracy), they are digital I2C temperature sensors that are very easy to
work with (don't need to worry about an ADC). There is tons of bit banged
I2C PIC code out there for you to use, although writing it yourself would be
pretty trivial. As for controlling the heater can I assume it is a 115V or
230V AC resistive heater? If so then I would suggest an optoisolator and
triac to control it, they should be the easiest to work with. The rest is
all software which is mostly trivial. If you have trouble on that front let
us know. Thanks, TTYL

> {Original Message removed}

2002\04\15@142614 by 1?B?c2FtbyBiZW5lZGnoaeg=?=

I once experimented with Dallas Semiconductor DS1620 digital thermometer and
thermostat  ( controlled via 3 pins, 0.5°C or better accuracy, cheap, -25 to
125°C range) and for that I can also dig out the code.
Regards, Samo


{Original Message removed}

2002\04\15@151909 by Nick Veys

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I second that, the 1620 is an excellent device, and has Temp High and
Temp Low interrupts which would be quite useful in your application.

EraseMEnickspamveys.com | http://www.veys.com/nick
> {Original Message removed}

2002\04\15@160829 by Barry Gershenfeld

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He told us what he really needs:

> In fact I need chocolate to reach 44 o C as quickly
> as i can .... The point is not to pass this temperture border.

This is a control-systems problem.  I'm not sure how I'd proceed
but this sounds like a job for a PID algorithm.

Barry

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2002\04\15@164219 by Augusto de Conto

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I don't know your experience with control...
First you have to take the model of the system.
Termal system generaly are very slow,
a first order system should be enoght.
It will result in a second order system you
consider the resistence Tranfer Function.
In this case I think that just a PI controler is
necessary. The diferencial controler wont
contribute too much and will insert noise
problems.

The PI algorithm is something like this:

Loop any 10ms (SampleRate)
   Error = Temperature_Reference - Temperature_Read
   ProportionalValue = kc * Error
   IntegralValue = LastIntegralValue + ( ki * (Error + LastError) *
(SampleRate / 2))
   Output = ProportionalValue + IntegralValue
   SaveLastValues()
EndLoop
kc is the proportional gain and
ki the integral gain
The problem, that is not too much problem
is to calculate this.

I hope bein usefull

Augusto Marasca de Conto
RemoveMEaugustospam_OUTspamKILLspamautomacao.eng.br



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2002\04\15@170504 by Chris Loiacono

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The "D" in PID refers to a DERIVATIVE function that is necessary when the
process model includes rapid "Disturbances". In this case, if the oven
enclosure could be opened during a process cycle the PV would drop
suddenly - this is a typical disturbance. Derivative provides an
appropriately large adjustment to the result, or output, which causes the
system to recover quickly, with less hysteresis.
If your process will not regularly be disturbed you will only need a
Proportional and Integral control system. If the process is expected to be a
slow one - minutes of heating to reach the SV, and there is considerable
room for PV hysteresis, say 10% or more of the overall deltaT, you can get
away with Proportional control only.

As a side note: When you get to the point of writing your algorithm, you may
consider representing the Proportional value as a "Band" instead of Gain.
Most EE's & programmers tend to think in terms that make it easier to use a
"Gain" value, but in the real world, tuning such a system is made about 10X
easier when you can plot and visualize your system on a simple 2D plot -
which a PB, or Proportional Band allows you to do easily. In other words,
more work up front = easier system set-up later.

Chris
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