Temperature Sensor Temperature measurement signal amplifier
First, the temperature sensor signal standards:
Select the temperature sensor is mainly based on the measurement range.
1>, when the measurement range is expected within the total range, Optional platinum resistance sensor.
2>, the narrow range usually requires the sensor must have a very high basic resistance, In order to obtain a sufficiently large resistance variation. Thermistors provided sufficiently large resistance change, Making these sensing elements ideal for a narrow measurement range.
3>, if the measurement range is quite large,Thermocouples are more suitable. Preferably the freezing point is also included in this range, Because the thermocouple indexing table is based on this temperature.
Second, the thermal resistance temperature sensor signal converter:
Selecting the appropriate temperature sensor for a particular application depends on the temperature range to be measured and the required accuracy. The system accuracy depends on the accuracy of the temperature sensor and the performance of the analog-to-digital converter digitizing the sensor output. In most cases,As the sensor signal is very weak, A high-resolution analog-to-digital converter is therefore required. Sigma-delta analog-to-digital converter with high resolution, And thus very suitable for such a system, And this converter often contains the required temperature measurement system built-in circuit, Such as the excitation current source. This application note focuses on the available thermal resistance temperature sensors (thermocouples, resistance temperature detectors (RTDs), thermistors and thermal diodes) and the circuitry required to connect the sensors to the analog-to-digital converter. And describes the performance requirements for analog-to-digital converters.
Third, the thermocouple temperature sensor signal converter:
The thermocouple temperature sensor consists of two different types of metal. When the temperature is higher than zero degrees Celsius, In the two metal connections will have a temperature difference voltage. The magnitude of the voltage depends on the temperature deviation from zero degrees Celsius. Thermocouple temperature sensor with a small size, Durable, the price is relatively cheap, Wide operating temperature range, etc., Very suitable for harsh environments in the very high temperature (up to 2300 ° C) measurement.
However, the thermocouple temperature sensor output is millivolt level,So need to go through the precision amplification to carry on further processing. Different types of thermocouple temperature sensor sensitivity is not the same, Generally only a few millivolts per degree Celsius, Therefore, in order to accurately read the temperature,Need high resolution, Low-noise analog-to-digital converter. When the thermocouple temperature sensor and printed circuit board copper print wire connection, Another thermocouple junction occurs where the thermocouple connects to the copper print wire. The result is a voltage that cancels the thermocouple voltage. In order to compensate for this reverse voltage, We place a temperature sensor at the thermocouple-copper connection, Measure the temperature at the junction. This is the so-called cold junction.