(Please visit the site to view this file)Hi Vicenzo, Our requirements are one pH sesnor (+/- 0.1 accuracy) - two 3-wire RTD's (0-50 oC 0.1 oC accuracy) sampling rate 5Hz! The sampling procedure will be - pH: (a) Turn On VREF (b) Read pH (AIN1 - AIN0) - RTD1: (a) Turn On IEXC1 & IEXC2 (b) Read RTD_1 (AIN3 - AIN2) - RTD2: (a) Turn On IEXC4 & IEXC5 (b) Read RTD_1 (AIN7 - AIN6) (-if not RTD is connected you have 0V reference so you can't sense the pH sensor as well) The ADS1248 VREF will be used for pH amp VREF, so REFP0 & REFN0 are disconnected from VREFOUT & VREFCOM! (- tha max REF voltage is VA - AN_GND - 1V, so having R46 = 3.3K means that the max IEXC is much less than 1mA; while if you are planning 1mA IEXC then you have to increase VA (that is decoupled from VD)) Updated to 820R! (- what's the purpose of R4 / R94, since that is not the normal position for the compensating resistors?) They are for compansation! (Corrected!) (- C6 nad C80 must be placed very close to IC47) C6 & C80 or C74 & C42? Also, should I open a new topic to ADS 1248? Could you transfer this topic? Thank you very much! Nikos
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