How to calculate J-Type Thermocouple Temperature using ADS1118?

Thanks for your instant reply.

Yes the information is given in datasheet, which is as follow:-

The procedure to actually achieve cold-junction compensation is simple and can be done in several ways. One
way is to interleave readings between the thermocouple inputs and the temperature sensor. That is, acquire one
on-chip temperature result for every thermocouple ADC voltage measured. If the cold junction is in a very stable
environment, more periodic cold junction measurements may be sufficient. These operations yield two results for
every thermocouple measurement and cold junction measurement cycle: the thermocouple voltage V TC and the
on-chip temperature T CJC . In order to account for the cold junction, the temperature sensor within the ADS1118
must first be converted to a voltage proportional to the thermocouple currently being used yielding V CJC . This
conversion is generally accomplished by performing a reverse lookup on the table being used for the
thermocouple voltage to temperature conversion. Then, adding the two voltages yields the thermocouple
compensated voltage (V Actual ), where V CJC + V TC = V Actual . V Actual is then converted to temperature using the
same lookup table as before, yielding T Actual .

Joseph Wu thanks for your reply,

I am getting same internal temperature data for both differential channels,

Here is my Code:-

_TC_Comm_16(TC_TEMP); // discard data, configure TC_TEMP
thermo.tc_dev1.cj_temp = _TC_Comm_16(TC_TC01); // read TC_TEMP, configure TC_TC01
Serial.println(thermo.tc_dev1.cj_temp,HEX);
_TC_Comm_16(TC_TC01); // discard data, configure TC_TC01
tc_dev1.thermocouple1 = _TC_Comm_16(TC_TC23); // read TC_TC01, configure TC_TC02
Serial.println(thermo.tc_dev1.thermocouple1,HEX);
_TC_Comm_16(TC_TC23); // discard data, configure TC_TC23 
thermo.tc_dev1.thermocouple2 = _TC_Comm_16(TC_TEMP); // read TC_TC02, configure TC_TEMP
Serial.println(thermo.tc_dev1.thermocouple2,HEX);

and the function is as follow:-

static u16_t _TC_Comm_16(u16_t config_word)
{
u16_t ret_val;
u8_t comm_byte; 
// set SS pin LOW (enable)
digitalWrite(SS, LOW); 
// send command
comm_byte = SPI.transfer(HI16(config_word)); // Data MSB
ret_val = (u16_t)comm_byte;
comm_byte = SPI.transfer(LO16(config_word)); // Data LSB
ret_val = (ret_val << 8) | (u16_t)comm_byte;

// set SS pin HIGH (disable)
digitalWrite(SS, HIGH);
return ret_val;
}

No thermocouple is connected right now, i must get full swing of voltage.

_TC_Comm_16(TC_TEMP); // discard data, configure TC_TEMP
delay(150);
thermo.tc_dev1.cj_temp = _TC_Comm_16(TC_TC01); // read TC_TEMP, configure TC_TC01
delay(150);
Serial.println(thermo.tc_dev1.cj_temp,HEX);
_TC_Comm_16(TC_TC01); // discard data, configure TC_TC01
delay(150);
tc_dev1.thermocouple1 = _TC_Comm_16(TC_TC23); // read TC_TC01, configure TC_TC02
delay(150);
Serial.println(thermo.tc_dev1.thermocouple1,HEX);
_TC_Comm_16(TC_TC23); // discard data, configure TC_TC23 
delay(150);
thermo.tc_dev1.thermocouple2 = _TC_Comm_16(TC_TEMP); // read TC_TC02, configure TC_TEMP
delay(150);
Serial.println(thermo.tc_dev1.thermocouple2,HEX);

After adding the delay of 150 millisconds i am getting the following results:-

CD4 => 25.65 deg Celcius (Internal Temperature)
7FFF => This is for thermocouple 1 Port (No Thermocouple is connected, that's why i am getting 7FFF full swing i think)
7FFF => This is for thermocouple 2 Port (No Thermocouple is connected, that's why i am getting 7FFF full swing i think)

Previously i am getting the same value is due to the fact that the conversion for differential channels are not completed and i am reading the old data of internal temperature. Please correct me if i am wrong some where.

One strange thing is that, when i connect thermocouple in the thermocouple connector, i am getting 0/1/2/3 Hex values on the channel the thermocouple is connected.
Right now i don't know which thermocouple is this which i am connecting (as we have ordered J-Type but it will take some time), but i can tell the colors of wires, one is yellow and another is red.
And at other end it is having a connector like this.

I am trying to understand the whole application, that's why asking basic questions.

As per this link, from NI website

I found that i am using K-type thermocouple because color is red and yellow.

But the main problem is that why i am not getting voltage when connecting this thermocouple to thermocouple connector.