At 07:01 AM 8/15/02 +0100, you wrote:
>Hello,
>
>I'm designing a PIC16F877 based temperature controller
>(with LCD, keypad, optocoupler etc.). I'll be using a
>Pt100 RTD as the sensor. Range is from 0C to 499.5C
>with steps of 0.5C. I'd like to give the user an
>option to calibrate the controller. How do I do this?
>(I mean, how should the calibration be done?)

Assuming you really mean "calibrate the controller"
(not the system), what reference do you expect the
user to have in order to perform the calibration?
If s/he is expected to have the usual NIST-traceable
(or equivalent) resistance box, then you can calibrate
by storing zero offset and span adjustment numbers
in EEPROM. Is that what you mean? In that case, it's
relatively straightforward.

>  Or am I
>right in using a Pt100 as the sensor, which can let
>the user calibrate the controller "on the fly"?

Don't understand this at all, sorry. What difference
does the sensor type make?  Sure you could throw in
resistors with the controller, but why would they be
more stable than the resistors actually used in your
design? Or am I guessing wrong here??

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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