DB-889D provides 16-channel analog input and CJC circuit for thermocouple input.
THERMO-COUPLE with CJC we would like the A/D card to read only V1, but by connecting the DB-889D in attempt to measure the output of junction J1, we have created two more metallic junction: J2 and J3, since J3 is a copper to copper junction, It creates no thermal EMF (V3=0) but J2 is a copper-to-constantan junction which will add an EMF(V2) In oppositional to the temperature dif-frewnce between J1 and J2. This says that we can't find the temperature at J1 unless we first find the temperature of J2. |