毕设翻译

一 单片机温度控制系统的组成及工作原理

1.在工业生产中, 对温度控制系统的要求, 主要是保证炉温按规定的温度工艺曲线变化,超调小或者无超调, 稳定性好, 不振荡, 对系统的快速性要求不高。以下浅析了单片机电阻炉控温系统设计过程及实现方法。热电偶将炉温变换为模拟电压信号, 经低通滤波滤掉干扰信号后送放大器, 信号放大为0～5 V 后送模/ 数转换器转换为数字量送单片机。同时, 热电偶的冷端温度也由IC 温度传感器变为电压信号, 经放大和转换后送单板机。标度变换程度根据温检测值求得实际炉温 θ。数字调节器程序根据恒温给定值θ0 与θ的偏差Δθ, 按积分分离的PID 控制算法得到输出控制量ui 。数字触发器程序根据uc 控制电阻炉子的导通时间, 调节炉温的变化使之与给定恒温值一致。导通时间长, 输出功率大, 温度升高快; 导通时间短, 输出功率小, 温度升高变慢。显示与恒温判断程序完成炉温θ与恒温时间显示、恒温开始与恒温完成判别、恒温完成时给出声光指示信号。断偶判断程序根据温度检测值判断温度传感是否开路, 若开路, 则给出断偶报警信号。

2.温度检测的设计采用热电偶传感器。热电偶传感器具有价廉、精度高、构造简单、测量范围宽(通常从- 50～ + 1600 ℃) 及反应快速的优点。热电偶传感器输出的电压信号较为微弱(只有几毫伏到几十毫伏) , 因此在进行A/ D 转换之前必须进行信号调理, 由高放大倍数的电路将它放大到A/ D 转换器通常所要求的伏特级电平。一般采用热电偶调理模板或调理模块来完成这项工作最为便捷, 而自行设计、制作仪表放大器则较为繁琐且较难保证精度。图2 冷端温度检测与放大电路使用热电偶传感器应注意采取冷端补偿。即当热电偶冷端温度不为0 ℃时, 热电偶的输出电势将

偏离冷端温度为0 ℃时的数值, 为了提高测温精度, 需要采取冷端补偿措施。冷端温度检测电路如图2 所示。冷端补偿可以采用软件补偿方法, 用IC 温度传感器检测热电偶

在现代化的工业生产中，电流、电压、温度、压力、流量、流速和开关量都是常用的主要被控参数。例如：在冶金工业、化工生产、电力工程、造纸行业、机械制造和食品加工等诸多领域中，人们都需要对各类加热炉、热处理炉、反应炉和锅炉中的温度进行检测和控制。采用MCS-51单片机来对温度进行控制，不仅具有控制方便、组态简单和灵活性大等优点，而且可以大幅度提高被控温度的技术指标，从而能够大大提高产品的质量和数量。因此，单片机对温度的控制问题是一个工业生产中经常会遇到的问题。本文以它为例进行介绍，希望能收到举一反三和触类旁通的效果。 温度是工业对象中主要的被控参数之一，象冶金、机械、食品、化工各类工业中，广泛使用的各种加热炉、热处理炉、反应炉等，对工件的处理温度要求严格控制，计算机温度控制系统使温度控制指标得到了大幅度提高。

电阻炉炉温控制系统的控制过程是：单片机定时对炉温进行检测，经A/D转换芯片得到相应的数字量，经过计算机进行数据转换，得到应有的控制量，去控制加热功率，从而实现对温度的控制。 进行系统设计时应考虑如下问题：

炉温变化规律的控制，即炉温按预定的温度——时间关系变化，这主要在控制程序设计中考虑。温度控制范围：如400~1000℃，这就涉及到测温元件、电炉功率的选择等。控制精度、超调量等指标，这涉及到A/D转换精度、控制规律选择等。 二 硬件电路设计

1.温度检测元件及变送器、ADC的选择

温度检测元件及变送器的选择要考虑温度控制范围及精度要求。对于0~1000℃的测量范围，采用热电偶，如镍铬热电偶，分度号为EU，其输出信号为0~41.32mV，经毫伏变送器，输出0~10mA，然后再经过电流——电压变换电路转换为0~5V电压信号。为了提高测量精度，可将变送器进行零点迁移，例如温度测量范围改为400~1000℃，热电偶给出16.4~41.32mV时，使变送器输出0~10mV，这样使用8位A/D转换器，能使量化误差达到±2.34℃。 2.接口芯片的扩展

由于本系统既要显示、报警、键盘输入，又要进行控制，所以系统在8031系统中扩展了一片8155，它有三个8位I/O口，256字节的RAM，可以作为外部数据存储器供系统使用，8031的P2.1接8155的CE，P2.0接8155的IO/M，当P2.1＝0，P2.0＝1时，选中8155片内的三个I/O端口，其口地址如下：

0100H〖〗命令状态寄存器0101H〖〗A口0102H〖〗B口0103H〖〗C口或控制口寄存器0104H〖〗计数值低八位0105H〖〗计数值高八位和方式寄存器当P2.2＝0时，选中ADC0809（允许启动各通道转换与读取相应的转换结果）。转换结束信号EOC经倒相后接至单片机的外部中断INT1（P3.3），当P3.3＝0时，说明转换结束。我们选用0通道作为输入，把0809视为一个地址为03F8H的外部数据存储单元，对其写数据时，8031的WR信号使ALE和START有效，将74LS373锁存的地址低三位存入0809，并启动ADC0809，D 9EOC为低电平时，A/D转换正在进行，当EOC为高电平时，表示转换结束，8031可以读如转换好的数据。 3.温度控制电路

温度控制电路采用晶闸管调功方式。双向晶闸管串在50Hz交流电源和加热丝电路中，只要在给定周期里改变晶闸管开关的接通时

间的脉冲信号即可。这可以用一条I/O线，通过程序输出控制脉冲。为了达到过零触发的目的，需要交流电过零检测电路。此电路输出对应于50Hz交流电压过零时刻的脉冲，作为触发双向晶闸管的同步脉冲，使晶闸管，在交流电压过零时刻导通。

电压比较器LM311将50HZ正弦交流电压变成方波。方波上升沿和下降沿分别作为单稳态触发器的触发信号，单稳触发器输出的窄脉冲经二极管或门混合，就得到对应于220V市电过零时刻的同步脉冲。此脉冲一路作为触发同步脉冲加到温控电路，一路作为计数脉冲加到单片机8031的P3.4和P3.5输入端。 三 控制规律的选择和程序设计

电阻炉炉温控制是这样一个反馈调节过程，比较实际炉温和需要炉温得到偏差，通过对偏差的处理获得控制信号，去调节电阻炉的热功率，从而实现对炉温的控制。按照偏差的比例、积分和微分产生控制作用（PID控制），是过程控制中应用最广泛的一种控制形式。计算机PID是用差分方程近似实现的。PID调节规律的微分方程（略）。系统控制程序采用两重中断嵌套方式设计。首先使T0计数器产生定时中断，作为本系统的采样周期。在中断服务程序中启动A/D，读入采样数据，进行数字滤波、上下限报警处理，PID计算，然后输出控制脉冲信号。脉冲宽度由T1计数器溢出中断决定。在等待T1中断时，将本次采样值转换成对应的温度值放入显示缓冲区，然后调用显示子程序。从T1中断返回后，再从T0中断返回主程序并且、继续显示本次采样温度，等待下次T0中断。 自从1976年Intel公司推出第一批单片机以来，80年代单片机技术进入快速发展时期，近年来，随着大规模集成电路的发展，单片机继续朝快速、高性能方向发展，从4位、8位单片机发展到16位、32位单片机。单片机主要用于控制，它的应用领域遍及各

行各业，大到航天飞机，小至日常生活中的冰箱、彩电，单片机都可以大显其能。单片机在国内的三大领域中应用得十分广泛：第一是家用电器业，例如全自动洗衣机、智能玩具；第二是通讯业，包括电话、手机和BP机等等；第三是仪器仪表和计算机外设制造，例如软盘、硬盘、收银机、电表。除了上述传统领域外，汽车、电子工业在国外也是单片机应用十分广泛的一个领域。它成本低、集成度高、功耗低、控制功能多能灵活的组装成各种智能控制装置，由它构成的智能仪表解决了长期以来测量仪器中的误差的修正、线性处理等问题。

单片机将微处理器、存储器、定时/计数器、I/O接口电路等集成在一个芯片上的大规模集成电路，本身即是一个小型化的微机系统。单片机技术与传感与测量技术、信号与系统分析技术、电路设计技术、可编程逻辑应用技术、微机接口技术、数据库技术以及数据结构、计算机操作系统、汇编语言程序设计、高级语言程序设计、软件工程、数据网络通信、数字信号处理、自动控制、误差分析、仪器仪表结构设计和制造工艺等的结合，使得单片机的应用非常广泛。同时，单片机具有较强的管理功能。采用单片机对整个测量电路进行管理和控制，使得整个系统智能化、功耗低、使用电子元件较少、内部配线少、成本低，制造、安装、调试及维修方便。

用温度传感器将被测温度转换为电量，经过放大滤波电路处理后，由模数转换器将模拟量转换为数字量，再与单片机相连，通过可编程键盘显示接口芯片实现温度限值的设定。最后通过小键盘控制数码管显示所需要的某路温度值。

1.被测量经过温度传感器转换为电量，再放大后送给A/D转换器。 2.电量经过A/D转换为二进制数值，送给8031单片机，8031单片

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

temperature detector of choice and the choice of transmitter to consider the scope and accuracy of temperature control. 0~1000 ° C for the measurement using thermocouples, such as nickel chromium thermocouple, Graduation for the EU. 0~41.32mV output signals, millivolt transmitter output 0~10mA. -- then read current voltage conversion circuit voltage op. To improve the measurement accuracy of 0.1 for transmitter can be relocated. changed 400~1000 ° C temperature range, given 16.4~41.32mV thermocouple, Transmitter output 0~10mV so that the use of 8-bit ADC, quantization error of ± 2.34 ° C make. 2. Due to the expansion of the system interface chip to show both the police and keyboard input, but also control, Therefore, the expansion of the system in 8031 was 8,155, which has three eight Interface. 256 bytes of RAM can be used as an external data storage for the system. 8031 P2.1 accept the CE 8155, then 8155's P2.0 IO/M. When P2.1=0, P2.0=1, the three films selected 8,155 / port, port addresses are as follows :Register 0101H 0100H [] [] A state order mouth I 0103H 0102H [B] [C] I control the population register or low numerical terms eight 0105H 0104H [] [] high eight dollars and numerical methods Register When P2.2=0, selected ADCO8O9 (allowing access conversion and start reading the results of conversion). EOC signal conversion by the end of inverter followed disruption to the external MCU INT1 (P3.3). When P3.3=0, to translate the end. We will use as input channel 0, 0809 as a 03F8H address of the external data storage unit its written data, the WR 8031 and the START ALE signal so effective, 74LS373 latch the address will be deposited in three low 0809 and started ADCO8O9. D. 9EOC of low level, ongoing D conversion, switching to the EOC, said the end of conversion, 8031 can be read as good data conversion. 3. Temperature control circuit temperature control circuit Thyrister-way. Triac Series 50Hz AC power and heating wire in the circuit. If change thyristor switches in a given cycle time of the pulse signal can be connected. This can be one / line through export control procedures pulse.

To achieve zero trigger the end, AC zero-crossing detection circuit. 50Hz AC voltage corresponding to the circuit output pulse zero moment, as the simultaneous bidirectional thyristor trigger pulse, thyristor make the AC voltage zero conduction time. LM311 voltage comparator to 50HZ AC voltage into a square. Square, as the rising or

falling transition triggered monostable multivibrator signal Trigger pulse output stability of the single narrow door on the diode or mixed 220V power -- be it corresponds to the zero-crossing time synchronization pulse. This way as a trigger pulse synchronization pulse upon the temperature control circuit. SCM 8031 as a way of counting pulses added to the P3.4 and P3.5 input. (3) the laws and procedures designed to control the Resistance Heater Control is a feedback process Temperature and Temperature needs to be more practical deviation of the error signal processing controlled, The power to regulate the resistance furnace, the furnace temperature control to achieve.According to the error ratio, integral and differential have control (PID). process control is the most widely used form of a control. PID is the approximate difference equations using computers to achieve. PID law equation (abbreviated). Interrupt nesting mode using dual control system design process.

First make T0 Counter regularly interrupted, as the system's sampling period. D process started in a break in service, reading the data sampling, digital filtering, on the threshold alarm, PID, and then pulse output control signals. T1 pulse width counter overflow interrupted by the decision. T1 suspended pending, this sampling will be converted into the corresponding temperature display buffer. Then call display subroutine. T1 return from the suspension, then returned to the main program and suspended from T0, continue to show this sample temperature T0 waiting for the next interruption. Since 1976, Intel introduced the first batch of SCM, SCM technology into the 1980s, the period of rapid development in recent years, with the development of large-scale integrated circuits. SCM will continue rapid development of high-performance, four, 8-bit MCU to 16-bit and 32-bit MCU. SCM mainly used to control its application across the board, to the space shuttle, small refrigerators to daily life. color televisions, big MCU can display their talents. SCM in the three areas are very broad application : The first is household appliances industry, such as automatic washing machines, smart toys; Second, the communications industry, including telephone, cell phone and pager, etc.;The third is to create instrumentation and computer peripherals, such as floppy disks, hard disks, cash registers, meters. In addition to these traditional spheres, automobiles, electronics industry and foreign SCM application is a very broad field. It is low cost, high integration,

low power and control functions into a more flexible assembly of intelligent control devices. by the intelligent instrument it constitutes a long time to resolve the errors of measurement instruments, linear address other issues. SCM will microprocessor, memory, timer / counter, / interface integrated circuit on a chip of large-scale integrated circuits, the computer itself is a small system. SCM technology and sensor technology, and signal analysis technology, circuit design technology programmable logic technology, computer interface technology, database technology and data structure of the computer operating system, assembly language programming, high-level language programming, software engineering, data communication networks, digital signal processing, control, Error analysis, instrument design and manufacturing techniques, etc., and makes extensive use of the MCU. Meanwhile, SCM has strong management functions. Single chip measurement circuit of the entire management and control, which makes the system intelligent, and low power consumption. less use of electronic components and internal wiring small, low cost, manufacturing, installation, commissioning and maintenance convenience.

Temperature sensors will be converted into electricity measured temperature, after amplification circuit filter processing, ADC conversion from analog to digita

l, connected with the MCU. Programmable keyboard and display interface to the chip set temperature limits. Finally, the small keyboard control LED shows need a road temperature. 1. After measuring the temperature sensor has been converted to electricity and then gave amplified ADC.

2. After conversion of binary-D numerical electricity, gave 8031. According to the 8031 software is designed to accomplish.

3. Disposed, sending keyboard and display processing chips, and then from Digital Display.

4. If the temperature exceeds limits established by the temperature, turn alarm processing. 5. Small ones from the keyboard shows the temperature control requirements.

The choice of sensors used mainly thermocouple temperature detector, thermal resistance, thermal resistance, etc.. Thermocouple mainly using the thermoelectric effect of two different metals have potential contact with the temperature change, which Temperature in

order to achieve the objective. Accurate measurement, temperature measurement moderate price range, linearity better. However, its output voltage by the end of the cold temperature, the need for cold temperature compensation, the circuit complexity China is not the best option in this issue. Thermistor or metal oxide semiconductor materials by high sensitivity, small thermal inertia, long life, low prices. But measuring the stability and repeatability is poor, unable to meet the measurement accuracy of 0.2 ° C to give some of the requirements. Poor linearity and the need for look-up table linear regression, a lot of waste of resources controller, it is not selected. The thermal resistance is the use of metal resistivity with temperature changes and changes in the characteristics of temperature into volume resistivity volume. The advantage is high accuracy and high stability, high reliability, small thermal inertia, rehabilitation is good, moderate price. It is linear with temperature resistance, thermal resistance Pt100, 0 \℃ expressed by the following equation :Which A=3.9083 ╳ 10-3 / ;B=-5.775 ╳ 10-7 ° C / ° C; This shows that The higher the temperature the greater the non-linear error, the scope of this topic demands Temperature -90 ° C and 40 ° C, lower temperatures. When the calculated temperature of 90 ° C, nonlinearity error of 0.34%. The least square method is suitable for 0.1 and gain adjustment, but also to make the same error twice reduced and the accuracy of the stated requirements. 0.2/90=0.22%, this issue should be selected Pt100 resistance, Approximate values and temperature resistance can be seen as linear.

2, amplifier thermal resistance measured resistance is the amount needed to be translated into voltage controller can be collected. Basic resistance-voltage conversion circuit is fixed with another series resistance, but this way, When the output level for non-zero temperature range, is not conducive to the small signal amplification and D conversion accuracy. Therefore, the use of bridge work measurement circuit which is shown in figure 2 : R1R2 Ω for a fixed voltage resistance, Rt thermal resistance, Rw2 to zero resistance, as the two make it the same way current and keeps constant, output voltage adjustable Rt0=Rw2, which makes R1 bridge in the great output avoids making small changes. When the Rt changes from 0 to 100 ° C, only 10 mV output, it still needs to conduct small-signal amplification. The works are low-frequency gain adjustable amplifier circuit in

Figure 3 :Rw1 to gain resistance which, adjusted for measuring full range, low-noise operational amplifier used NE5532. Order R2, R3=R4, R5=R6, then the total gain amplifier. When Rw1 from 0 to 50k Ω change, ∞ Av changed in the range of 150 to meet the requirements necessary gains.

3, D conversion subject to the requirements of measurement accuracy of 0.2 ° C degrees. Temperature should be the scope of the requirements for the maximum temperature to room temperature, 20 to 90 ℃. This determines the minimum resolution of not less than 0.2/ D conversion (90-20) =1/350. D conversion chip can reach ordinary eight 1/256 not meet the requirements. If the chips use a higher place, it will greatly increase the cost. Is a time constant temperature changes in the larger variables, D conversion rate of a modest, therefore, the design was chosen VCO first voltage signal into a frequency volume, Counting through the controller function into a digital signal, which could greatly improve the accuracy and cost savings.

4, the temperature controller error feedback control it will be used classical control theory of PID (Proportional Integral and Derivative proportional integral differential) control, the controller can take a number of options, such as analog circuits. microcontroller, such as logic devices. Analog circuit can be controlled to change for the error control technology is mature, more stable performance. However, the drawback is not easy, tuning PID parameters need replacement parts, and vulnerable to outside interference. Now in the digital era has become highly developed eliminated. SCM as a branch of micro-computer, and more than 20 years of development, have a wide range of applications in the field of control. Moreover, in recent years, with the FPGA (field programmable gate array) has been engaged to represent the programmable logic device. SCM makes up for their excellent performance significantly slower to respond, the less disruption source shortcomings. However, the FPGA computing capacity is limited, therefore, we used in the design of the FPGA and microprocessor control method combining two complementary strengths, greatly improving performance. In the book, the VCO signal FPGA is mainly responsible for receiving, and the pulse is obtained by measuring its voltage; SCM receiving FPGA transmitted data and show that PID operation, and output

5, the output drive circuit PID controller to the computational results

into different pulse duty cycle output The agencies also need to read the signals role in the implementation of drive circuit. The AC power control circuit works, about a few cycle load connected with the AC power supply, and calls for a few cycle. open and continuous cycle by changing the ratio of the average power consumption load regulation. Specific circuit in Figure 5. 220V/50Hz power to the city, to 5V voltage division below, the input operational amplifier with an input. Operational Amplifier as a zero comparator, when electricity over night, jumping changed operational amplifier output to the clock terminal D flip-flop, SCM then the output of D flip-flop input pulse signal, the output of two-way thyristor gate. Thus, only when the AC off night, SCM thyristor output signal only have an effect in other words, Only when the AC off night, or turn-off thyristor can be opened. This can greatly reduce the opening-off thyristor impact on the process, reduce opening-off loss.

into different pulse duty cycle output The agencies also need to read the signals role in the implementation of drive circuit. The AC power control circuit works, about a few cycle load connected with the AC power supply, and calls for a few cycle. open and continuous cycle by changing the ratio of the average power consumption load regulation. Specific circuit in Figure 5. 220V/50Hz power to the city, to 5V voltage division below, the input operational amplifier with an input. Operational Amplifier as a zero comparator, when electricity over night, jumping changed operational amplifier output to the clock terminal D flip-flop, SCM then the output of D flip-flop input pulse signal, the output of two-way thyristor gate. Thus, only when the AC off night, SCM thyristor output signal only have an effect in other words, Only when the AC off night, or turn-off thyristor can be opened. This can greatly reduce the opening-off thyristor impact on the process, reduce opening-off loss.

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