To make accurate and repeatable measurements, you usually need some kind of circuit between the sensor and the measurement system. These circuits, called signal-conditioning circuits, may amplify the signal from the sensor, filter noise from the input signal, or provide an excitation signal to the sensor. To make the best measurements possible, you need to know the characteristics of the sensor you plan to use and the types of measurements you want to make. Once you have this information, you can select the appropriate signal-conditioning circuits and measurement system. Temperature measurements Perhaps the most common parameter that data-acquisition systems are expected to make is temperature.
Thermocouples are the most popular type of temperature sensor.
They are rugged, readily available from many sources, and operate over a wide temperature range. This junction of two dissimilar metals generates a voltage that varies with temperature. One of the difficulties you face when using thermocouples is terminating the leads. Connecting thermocouple leads to a terminal block creates two additional thermocouples where the leads connect to the terminals To make an accurate measurement, you have to compensate for these unwanted voltages. This process is called cold-junction compensation.