To use the calibration charts one of the junctions of the thermocouple must be located in an ice bath. This is inconvenient especially when multi-channel measurements are to be carried out. The circuit in Figure 2.18 eliminates the need for an ice point and compensates automatically for the room temperature. Here is the unknown temperature, and are the thermocouple wires, the room temperature and the voltmeter. is a DC voltage source that produces a thermo-emf corresponding to the temperature levels and C, for the pair of materials and . It uses a resistance thermometer (usually a semiconductor-based thermistor) to measure the absolute room temperature and converts it into a thermo-emf using the quadratic formula referred earlier. Hence the voltmeter senses the total thermo-emf