A thermistor is an electrical resistance, made of semiconducting material, that can be wired into a circuit. The semiconducting material is usually made of manganese oxides and nickel oxides. The thermistor works based on the principle that the electrical resistance of this material changes with temperature. A thermocouple, on the other hand, is made of two wires of different metals, such as copper and iron. The equal length wires are connected electrically together at one end and open at the other end. The principle is that if the open ends of the wires are at a fixed temperature and you change the temperature at the connected end, this generates a voltage between the two wires at the open end of the thermocouple.
With a thermistor, you could use an instrument that measures electrical resistance and connect it across the thermistor. You will measure a resistance change with a change in temperature. If you then refer to a table that lists temperature change versus resistance, you can find out the temperature from this table. In the case of a thermocouple, you will use an electrical circuit to measure the difference in voltage between the two wires at the open end and use this to measure the temperature difference between the two ends of the wires.
Thermistor or Thermocouple?
In general, thermocouple readings are more precise than thermistor readings. However, they react more slowly to changes in temperature. Thermistors are also more expensive generally than thermocouples, due to the need for an external power source and the device's circuitry. The decision to use one or the other will depend on your specific needs.