On 3/7/2010 9:17 AM, yamanoor sairam wrote:
>
> That was a very valuable suggestion. Thank you very much. I shall get
> back to you after trying the same. I have another doubt. Usually the
> ORP probes are calibrated with a solution of known potential. For eg:
> 200mV, 400mV, etc. If you dip your ORP electrode probe into the
> solution, you have to get the exact equivalent over the display. Some
> ORP display units come with a calibration option to adjust the
> values. As your probe ages, there may be some small signal losses
> which could be compensated using this option. I am planning to
> integrate this option to my PIC based probe. Lets assume that my
> display reads 196mV after x days when dipped into a 200mV solution. I
> am planning to add a calibrate button which when pressed while dipped
> in a 200mV solution, finds the actual difference between the read
> value and desired value and stores it in my  EEPROM. This value is
> added to all the adc readings until next calibration. Is this a good
> idea or better change the reference voltage of the PIC  or is there
> any other better option of doing it?
>
> Sairam
>

I would do it as you describe and store the value in the EEPROM. A 
common method is to also store a "factory default" value there as well 
with some means of resetting to the factory default calibration values.

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