导语：
该系统体积小、成本低、工作可靠，具有很高工程应用价值。系统稍加改动或扩展，还可以完成温度测量等功能。
摘要：
本文介绍了一种应用LM35温度传感器开发的温控系统，重点阐述了系统结构、工作原理以及采样值量化。同时对LM35传感器特性、系统硬件电路设计、软件设计也作了介绍。该系统体积小、成本低、工作可靠，具有很高工程应用价值。系统稍加改动或扩展，还可以完成温度测量等功能。
关键词：温度传感器 工作原理 硬件设计 软件设计
1．引言
在各类民用控制、工业控制以及航空航天技术方面，温度测量和temperature control得到了广泛使用。在很多工作场合，元器件工作temperature指标达不到工业级或普军级temperature要求，可以通过design 加温电路的办法得以解决。小型、高效率、高精度的temperature sensor已经越来越受到design者关注。本文介绍了一种基于LM35 temperature sensor开发的温控system hardware circuit及software design。
2．LM35 temperature sensor
LM35是NS公司生产的一款集成电路temperature sensor，它具有很高的work precision和较宽线性work范围，该device output voltage与摄氏度temperatures线性成比例。因而，从使用角度来说， LM35与用开尔文标准的linear temperature sensors相比更有优越之处，由于不需要外部校准或微调，可以提供±1/4℃常用的室温precision。此device work voltage为直流4～30V； work current为小于133μA； output voltage为+6V～-1.0V； output impedance为1mA负载时0.1Ω； precision为0.5℃精度（在+25℃时）； leakage current为小于60μA； linear coefficient 为10.0mV/℃； non-linearity value 为±1/4℃； calibration method 为直接用摄氏度temperatures calibration.; package type 为密封TO-46 crystal package or plastic TO-92 crystal package; operating temperature range 为-55～+150℃.
3．System Structure & Work Principle
The control system is composed of the following components: Temperature Sensor Circuit, Signal Conditioning Circuit, A/D Sampling Circuit, Microprocessor System, Output Control Circuit and Heating Circuit.The basic working principle of the system is as follows: The Temperature Sensor Circuit outputs a signal proportional to the ambient temperature to the Signal Conditioning Circuit through an amplifier with high gain and low noise; The amplified signal is then converted into a digital signal by an analog-to-digital converter (ADC) in the A/D Sampling Circuit; The microprocessor in the Microprocessor System processes this digital data and compares it with a predetermined threshold value to determine whether heating is required or not; If necessary, it controls the Output Control Circuit to turn on/off the Heating Circuit.
图一 Warmth Control System Block Diagram
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$$
e^x = e^{y-z} + e^{z-y}.
$$
Thus we have $a=3$, $b=2$, $c=5$. Plugging these values into our expression for $\frac{\partial z}{\partial x}$ gives us:
$$
\frac{\partial z}{\partial x} = -e^{-x+y-z}\cdot(x-y+z)+e^{-x+y-z}\cdot(y-x+z).
$$
Simplifying this expression gives us:
$$
\frac{\partial z}{\partial x} = -e^{-x+y-z}\cdot(x-y+z)+e^{-x+y-z}\cdot(y-x+z)
=\left(e^{-(x-y)}-\frac{x-y}{z}\right)\left(\frac{-z+x+y}{z}-y+x+\right)
=\left(\sqrt{x^2+(y+\right)^2}-y+\right)\left(-z+x+\right)
=-z+x-
=-z+
