How many bits will I need ??

[Calamar]

I need to desing a temperature controller
from 50ºC to 1200 ºC, I need to reach the set-point
and keep arround it, but for alinealitis in
the circuit(termocuples plus ...) it can be +/- 10ºC
of the realy temperature, but I need to controller
the temperature +/- 2ºC of the set-point ...
How many bits Will I need ??

I've made some smilliar design to it with
a Pt100(0ºC to 400 ºC), 16f873 (10 bits ADC),
and PID sowtware
it keep +/- 4LSB arround the setpoint I'd made
a well work or I can improve it ??

there are something in teh web that anyone of yours
could recomend me to read ??

(sorry my english)
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This message was ported from CCS's old forum
Original Post ID: 144515392
_________________
Best Regards
Daniel H. Sagarra
La Plata (Argentina)

[Kenny]

<font face="Courier New" size=-1>:=I need to desing a temperature controller
:=from 50ºC to 1200 ºC, I need to reach the set-point
:=and keep arround it, but for alinealitis in
:=the circuit(termocuples plus ...) it can be +/- 10ºC
:=of the realy temperature, but I need to controller
:=the temperature +/- 2ºC of the set-point ...
:= How many bits Will I need ??
:=
:=I've made some smilliar design to it with
:=a Pt100(0ºC to 400 ºC), 16f873 (10 bits ADC),
:=and PID sowtware
:=it keep +/- 4LSB arround the setpoint I'd made
:=a well work or I can improve it ??
:=
:=there are something in teh web that anyone of yours
:=could recomend me to read ??
:=
:=(sorry my english)
:=
:=
:=


+/- 2deg C is a real challenge and difficult to achieve I suspect.

Type K thermocouples are good for the temperature range.

A cheap conditioner is the AD595 from Analog Devices:
<a href="http://www.analog.com/UploadedFiles/Data_Sheets/421725987AD594_5_c.pdf" TARGET="_blank"> <a href="http://www.analog.com/UploadedFiles/Data_Sheets/421725987AD594_5_c.pdf" TARGET="_blank">http://www.analog.com/UploadedFiles/Data_Sheets/421725987AD594_5_c.pdf</a></a>

A much better one (but expensive)is the industry standard 5B module, eg the SCM5B47 from Dataforth:
<a href="http://www.dataforth.com" TARGET="_blank"> <a href="http://www.dataforth.com" TARGET="_blank">http://www.dataforth.com</a></a>

Appropriate one is the SCM5B47K-13 (-100 to +1300 deg C), output 0 to +5V.
Accuracy is +/- 1.2 deg C. Linearisation and isolation are taken care of by the module. This module needs a board (an accessory) to plug into that has the reference temperature sensor on it close to terminals for the thermocouple. Ambient temperature variation is another source of error in the measurement - the temperature compensation is not perfect.

You will need a 12 bit A/D to cover the range (there is a PIC that has this but I haven't used it). 10 bits will not give enough control.

Also thermocouples need to be calibrated because they vary in accuracy even between batches by up to several degrees.

Hope this helps
Kenny</font>
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This message was ported from CCS's old forum
Original Post ID: 144515412