to replace some high precision instrumentation for precision temperature measurements with RTDs I'm planning to use the ADS1248. Is it the best suited for that? Would it be much better to use the ADS1282 with 32bit and an external current source?
The ADS1282 has a combination of SINC and FIR Digital filters that provide a flat pass-band frequency response optimized for low frequency AC measurements typically used on seismic and energy exploration applications. The ADS1282 is optimized to provide results with excellent SNR and extremely low distortion required for those applications. Although the ADS1282 is the best modulator that offers the less noise and higher resolution, since you are making a temperature measurement that could be considered a DC measurement, you will probably need to take the conversion results of the ADS1282 and post process the conversion results of the ADS1282 with your own digital filter in order to resolve a very accurate DC measurement (for example you may want to reject 50/60Hz line noise). The ADS1282 modulator has been used in an ultra high resolution weight-scale systems with the appropriate signal post-processing.
The ADS1248 internal FIR filter is optimized for DC measurements. The internal filter can offer simultaneous 50/60Hz noise rejection at data rates of 5SPS, 10SPS and 20SPS. Line noise rejection is often very critical for DC measurements. In addition to the built in IDAC's; the device incorporates a Programmable Gain Amplifier to increase resolution in your measurement. The ADS1259 is another device that incorporates a digital filter optimized for very high precision DC measurements required on high precision instrumentation, also offering 50/60 Hz rejection. The ADS1259 device offers very low noise, low drift and high linearity; however, it does not incorporate the internal amplifier and the IDACs. If you use the ADS1248 (or ADS1259), the DC measurement conversion result obtained is ready to use without the need of external post-processing.
In general, the ADS1248 is a high accuracy solution that can easily meet/exceed Class A RTD standards incorporating the PGA amplifier and IDAC's. The ADS1282 modulator can give you ultimately the highest resolution when the appropriate digital filter post-processing is implemented. However, in many cases, the error and noise in the measurement will be probably dominated by other system and external sources of noise. You will need to also consider the accuracy that is guaranteed by the RTD sensor.
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