Hello Mr.BOB. Thank you for your support. I have changed my circuit of input in my schematic as follows. Here I have changed the supply AVDD = 2.5V and AVSS = -2.5V as according to you dual supply is required for grounded thermocouples. I have kept the schematic common for RTD type as I want to make the circuit common for T/C & RTD. Please check whether the circuit schematic as attached (Please visit the site to view this file)is OK.? Please refer sheet 2 and sheet 3 where through jumper S14 and S17 I have given 2.5V and -2.5V to AVDD and AVSS respectively.
Also I have taken care of CJC (temperature ) using external current source LM334 given to internal ADC using a stack connected as shown in sheet1 of my schematic via REL-3pin. The internal ADC code would be converted into equivalent mV and added with the mV obtained from ADS1148. I wanted to know whether the internal sensor of ADS1148 could be used for CJC calculation instead of LM334?
The differential cap would be 1UF instead of 0.1UF as shown in the schematic.
In my software as I have mentioned earlier the settings for thermocouple is as follows:
eg: channel1:
MUX0 = 41H
VBIAS = 02H
MUX1 = 30H
PGA = 50H
Please check whether the above settings are applicable for the new schematic and whether VBIAS would be required?
Best Regards,
Dhiren