机根据设计目的完成相应的软件处理。
3.处理完毕后，送键盘显示处理芯片，然后再由数码管显示。 4.如果温度超过所设温度限值，转报警处理程序。 5.由小键盘控制所需显示路数的温度。 四 传感器选择
常用的温度检测元件主要有热电偶、热电阻、热敏电阻等。热电偶主要是利用两种不同金属的热电效应，产生接触电势随温度变化而变化，从而达到测温的目的。测量准确，价格适中测温范围宽，线性度较好。但其输出电压受冷端温度影响，需要进行冷端温度补偿，使电路变得复杂，在本题中并非最佳方案。
热敏电阻由金属氧化物或半导体材料制成，灵敏度高、热惰性小、寿命长、价格便宜。但其测量的稳定性和复现性差，测量精度无法满足本题发挥部分0.2℃的要求。而且线性度差，需要进行查表线性拟合，大大浪费控制器的资源，因此不能选用。
热电阻是利用金属的电阻率随温度变化而变化的特性，将温度量转化成电阻量。其优点是准确度高，稳定性高，性能可靠，热惯性小、复现性好，价格适中。但电阻值与温度是非线性关系，Pt100热电阻，当0℃ 其中A=3.9083╳10-3 /℃；B=-5.775╳10-7 /℃；由此可见，温度越高非线性误差越大，本题目要求温控范围是40℃~90℃，温度较低。经计算当温度为90℃时，非线性误差为0.34%，运用最小二乘法适当的进行零点和增益的调整，还可使此误差降低一倍，而本题要求精度为，0.2/90=0.22%，因此在本题中可以选用Pt100热电阻，并可近似将其电阻值与温度看作线性关系。 2、 放大电路 热电阻所测得的是电阻量，需要转化为电压量才能被控制器采集。 最基本的电阻-电压转换电路是将其与另一固定电阻串联，但这种方法，当温度为量程下限时输出不为零，这样不利于小信号的放大和提高A/D转换的精度。因此，本作品采用桥路测量，电路如图2所示： 其中R1R2为10kΩ固定电阻，Rt为热电阻，Rw2为调零电阻，由于 ，因此上下两支路电流相等，并保持恒定不变，输出电压 ，可调整Rt0=Rw2，使得 由于在桥路中R1很大，使得输出量uo变化很小，当Rt从0到100℃变化时，输出仅有十几毫伏，因此还需要进行小信号放大。本作品所用低频增益可调放大电路如图3： 其中Rw1为增益电阻，用于调整测量满量程，运放采用低噪声NE5532，令R1=R2,R3=R4,R5=R6，则该放大电路总增益为 ，当Rw1从0到50kΩ变化时，Av的变化范围为150至+∞，满足所需增益要求。 3、 A/D转换 题目所要求测量度精度为0.2℃，测温的范围应该为室温到要求的最高温度，即20~90℃，这就决定了A/D转换的最低分辨率不低于0.2/（90-20）=1/350，而普通八位A/D转换芯片只能达到1/256，不能满足要求。而如果选用更高位的芯片，将大大增加成本。温度是一种变化时间常数较大的物理量，对A/D转换速度要求不高，因此，在设计中选用了压控振荡器，先将电压信号转化为频率量，再通过控制器的计数功能转化为数字信号，这样可以大大提高精度，节约成本。 4、 控制器 对水温的反馈偏差控制，就必然用到经典控制理论中的PID（Proportional Integral and Derivative比例积分微分）控制， 控制器可有多种选择，如模拟电路、单片机、逻辑器件等。 模拟电路控制可对偏差变化进行连续的控制，技术成熟，性能较稳定。但其缺点是不便于显示，调整PID参数需更换元器件，易受到外界干扰等，在现在这个数字化高度发展的时代已趋于淘汰。 单片机作为微型计算机的一个分支，已有二十多年的发展，在各控制领域都有广泛的应用。而近年以FPGA（现场可编程门阵列）为代表的可编程逻辑器件异军突起，其优异的性能大大弥补了单片机响应速度慢、中断源少的缺点。但FPGA的运算能力有限，因此，在我们的设计中采用FPGA与单片机相结合的控制方式，二者优势互补，性能大大提高。 在本作品中，FPGA主要负责接收压控振荡器的信号，通过测量其正脉宽而获得电压量；单片机接收FPGA发送的数据，进行显示、PID运算，和输出。 5、 输出驱动电路 控制器将其PID运算的结果转化为不同占空比的脉冲信号输出，该信号作用于执行机构还需要经过驱动电路。 本作品中采用交流调功电路，即将负载与交流电源接通几个周波，再断开几个周波，通过改变开通与断开周波的比值来调节负载所消耗的平均功率。具体实现电路如图5。 将220V/50Hz的市电，经电阻分压到5V以下，输入运放的同相输入端，运放作为过零比较器，当市电过零时，产生跳变，运放输出送到D触发器的时钟端，D触发器的输入接单片机输出的脉冲信号，输出接双向晶闸管的门极。这样，只有当交流电过零时，单片机的输出信号才对晶闸管产生作用，也就是说，只有当交流电过零时，晶闸管才能开通或关断。这样可以大大减小开通关断过程中对晶闸管的冲击，减少开通关断损耗。 SCM temperature control system in the industrial production structure and working principle of temperature control systems. Temperature is guaranteed by the change in temperature curve, without over-regulation or over-regulation of small, good stability, not shocks, Rapid modest nature of the system. On the following SCM resistance furnace temperature control system design and implementation. Temperature will transform to simulate thermal galvanic voltage, low-pass filter removes the interference signal amplifier evacuations, 0-5 V evacuation signal amplification to A / D conversion to digital converters sent MCU. Meanwhile, the cold spot temperature thermocouple temperature sensors into a voltage signal from the IC, then amplified and transformed SBC. Scaling transform degree temperature measurements obtained in accordance with the actual furnace temperature θ. Digital Controller under procedures set thermostats to the value of θ 0 errors Δ θ and θ. Integral separated by the PID control algorithm to control output volume Manuscripts. Digital Trigger uc control procedures under the conduction resistance furnace, the furnace temperature regulation changes to make it consistent with the duty to set thermostats.Conducting a long time, power output, temperature rises rapidly; Conducting a short time, the output power is a small temperature rises slowed. Temperature and temperature θ showed judgment procedures are completed time and temperature, with the temperature thermostats completed discrimination, - instructions for completing the warm voice signals. Dual Temperature Measurement value judgment procedures constantly under way to judge whether the temperature sensor that way, even given constantly alert signals. 2 thermocouple temperature sensor detection designs. Thermocouple sensor is inexpensive and high precision, simple structure, Measurement range (usually from-50 ～ 160 ° C) and the advantage of rapid response. Thermocouple sensor output voltage signals relatively weak (only a few tens of millivolt millivolt). Accordingly, before the need for signal conditioning Taking D conversion. The circuit by high magnification it magnified Taking D converter voltage level usually required level. Conditioning template thermocouple conditioning module normally used to complete this task or the most convenient and design, Instrumentation Amplifier also more difficult to produce more red tape to ensure accuracy.Figure 2 detection and amplification circuit temperature on the cold side should adopt the use of thermocouple cold junction compensation sensor. When the thermocouple cold junction temperature is 0 ° C, the output will thermocouple cold junction temperature from 0 ° C figure, In order to improve accuracy and the need for cold junction compensation. Cold-detection circuit shown in figure 2. Cold Junction Compensation Compensation software can be used with IC thermocouple temperature sensors In modern industrial production, current, voltage, temperature, pressure, flow, velocity and volume switches are commonly used parameters of the main accused. For example : in metallurgical industry, chemical industry, power engineering and paper industry, machinery manufacturing and food processing and many other fields. People need to have various types of furnace, heat treatment furnace, boiler, and the reactor temperature measurement and control. On the single-chip microcomputer to control the temperature is not only convenient control. simple and flexible configuration big advantages, it will greatly increase the temperature was charged with the technical indicators, thus can greatly enhance the quality and quantity of products. Therefore, the single-chip temperature control is a problem often encountered in industrial production problems. In this paper, it is carried out, and shared hopes to receive learned from the results. Industrial temperature is the main target was charged with one parameter, as metallurgy, machinery, food processing, chemical industries, extensive use of the furnace, heat treatment furnace, reactors, strictly control the temperature of the workpiece. Computer control temperature control system temperature indicators have been greatly improved. Resistance Heater Control System Temperature Control Processes : SCM regularly to detect D chip on the corresponding digital conversion through computer data conversion, it should control the volume Power to control heating, the temperature control. System design should consider the following questions : Temperature change control Temperature temperature -- that is the scheduled time for a change, it is mainly considered in the design control process. Temperature control : If 400~1000 ° C, which involves temperature measurement device, furnace power choices. Control precision, over-regulation and other indicators, which involved D conversion accuracy and control law choice. Hardware Design 1. Temperature detector and transmitter. ADC