Hi Philippe, let me know if the following clarifies things: 1) The schematic drawing above might be a little misleading, because I do not show the lead resistances of the RTDs. Following is a new drawing showing a potential solution with ADS1220 (again only for 2 RTDs, but you can extend the concept to 4 RTDs as well of course). In order to implement the lead resistance compensation using the two excitation current sources you will need one 2x 1:4 MUX to route the excitation currents to the RTDs. The 2nd 2x 1:4 MUX is needed to route the RTD voltage to the ADC inputs. 2) The ADS124S08 would be the best and most accurate single device solution to measure 4 thermocouples, but an ADS1220 with an external MUX would work as well. The connection of each thermocouple to the ADC would e.g. be implemented as shown in the ADS1220 datasheet. You need some means to bias the thermocouple to within the voltage range of the ADC. This can be implemented in multiple ways. What we usually show is the implementation using a pullup and pulldown resistor to the supplies (In case you have grounded thermocouples we need to implement this slightly differently). Besides biasing the thermocouple, this implementation can also serve to detect a broken thermocouple wire. Following the pullup/down resistors you would put a RC filter. You will also have to measure the cold junction temperature then. Customers use all different types of temperature sensors to measure the cold junction temperature: diodes, thermistors, RTDs, analog/digital output temperature sensors, etc. Regards,
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