Application of NTC temperature sensor.Infrared sensing module Processing

　　Temperature measurement is widely used. Not only does the production process require temperature control, some electronic products also need to measure their own temperature. For example, the computer needs to monitor the temperature of the CPU, the motor controller needs to know the temperature of the power driver IC, and so on. Temperature is a parameter that often needs to be tested in practical applications. From steel manufacturing to semiconductor production, many processes rely on temperature. Temperature sensors are the bridge between the application system and the real world. This article provides a brief overview of the various temperature sensors and describes the interface to the circuit system.

　　There are many types of sensors used to measure temperature, and thermistor is one of them. Many thermistors have a negative temperature coefficient (NTC), which means that their resistance value increases as the temperature decreases. Of all passive temperature sensors, thermistors have the highest sensitivity (that is, the change in resistance per degree change in temperature), but the thermistor's resistance/temperature curve is non-linear.

　　Table 1 is a typical NTC thermistor performance parameters.

　　These data are measured on Vishay-Dale thermistors, but they are also representative of NTC thermistors in general. The resistance value is given in the form of a ratio (R/R25), which represents the ratio of the resistance value at the current temperature to the resistance value at 25°C, usually the thermistor of the same series has similar characteristics and the same resistance / Temperature curve. Taking the thermistor series in Table 1 as an example, a resistor with a resistance of 10KΩ at 25°C has a resistance of 28.1KΩ at 0°C and a resistance of 4.086KΩ at 60°C; similarly, a resistor with a resistance of 5KΩ at 25°C The resistance of the thermistor at 0°C is 14.050KΩ.

　　Here T refers to the absolute temperature in Kelvin, and A, B, C, and D are constants, which vary according to the characteristics of the thermistor. These parameters are provided by the manufacturer of the thermistor.

　　Thermistors generally have a margin of error that specifies the consistency between samples. Depending on the material used, the error value is usually between 1% and 10%. Some thermistors are designed to be interchangeable in application and used in situations where field adjustment is not possible, such as an instrument, where the user or field engineer can only replace the thermistor without calibration, which is more accurate than ordinary thermistors Much taller and much more expensive.

　　Figure 2 is a typical circuit for measuring temperature using a thermistor. Resistor R1 pulls the thermistor's voltage up to the reference voltage, which is generally the same as the ADC's reference voltage, so if the ADC's reference voltage is 5V, Vref will also be 5V. The thermistor and the resistor are connected in series to generate a voltage divider, and the change in the resistance value causes the voltage at the node to change. The accuracy of the circuit depends on the error of the thermistor and the resistor and the accuracy of the reference voltage.

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