Hi Saumitra,
See my responses below in red. Remember that you still need to calibrate your system, as there are no ideal devices. The ratio of the RTD to the reference resistor is based on knowing precisely what the reference resistor is for the calculation. As this has some margin of error (tolerance), as does the accuracy of the RTD itself, your system will require calibration for a highly precise/accurate system.
Best regards,
Bob B
[quote user="Saumitra Deshpande"]
Hello Bob,
Thanks for the reply.
- I am issuing SELFOCAL at startup, but it has no effect on offset I am getting. BB> This may not be a huge error, but it will always add to total error and can be easily removed. All delta-sigma ADCs have some inherent offset.
- Since my desired range is 10-500 deg C, I can make R_COMP=0, will that have the desired effect ? BB> Making R_COMP 0 will remove the error caused by the resistor. 1% of 110 ohms is 1.1 ohms, which can result in up to a couple of degrees error without calibration. I would remove this resistance. The use of this resistor is much better in theory than in actual practice.
- By swapping the current sources you mean, converting same pair of channels but with alternate current source and then averaging the result ? BB> Yes, that is what I mean, but the need to do this is dramtically lessened if you remove or make R_COMP 0 ohms.
- I'll try replacing the ferrite with resistor. Does it need to be high precision/low ppm ? BB> This resistor does not need to be a precision resistor.
Thanks.
Saumitra A Deshpande
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