NTC热敏电阻分选仪介绍
NTC是负温度系数的英文缩写, 所谓NTC 热敏电阻分选仪就是负温度系数热敏电阻器。它是以锰、钴、镍和铜等金属氧化物为主要材料, 采用陶瓷工艺制造而成的。这些金属氧化物材料都具有半导体性质, 因为在导电方式上完全类似锗、硅等半导体材料。温度低时, 这些氧化物材料的载流子( 电子和孔穴) 数目少, 所以其电阻值较高; 随着温度的升高, 载流子数目增加, 所以电阻值降低。利用这一特性, 可将NTC 热敏电阻通过测量其电阻值来确定相应的温度, 从而达到检测和控制温度的目的。采用不同的制作工艺方法, 结构, 形状, 可以获得各种各样的NTC 热敏电阻, 它们广泛应用于温度测量, 温度补偿等领域。NTC 在生产出来后, 每个阻值随温度变化的特性并不一致, 这就需要对 NTC 按照不同的阻值变化范围进行分选。本系统以 PIC16F877A 芯片作为下位机控制NTC 分选过程, 采用8 位高速单片机C8051F022 做为核心的上位机进行数据管理, 串行EEPROM芯片来记录数据; 并利用 CH375 芯片将记录数据安全而准确地转储到U 盘上, 可以方便的对数据进行存储和管理, 并配以液晶显示屏, 人机交互更友好。该仪表具有分选准确, 运行稳定, 操作简便, 人机界面友好, 管理方便的优点。
1.电阻分选仪 下位机控制模块
PIC 系列单片机是美国微芯推出的CMOS 系列单片机, 该系列芯片采用精简指令集(RISC) , 哈佛总线结构, 2 级流水线取指令方式, 具有实用、低价、指令集小、简单易学、低功耗、高速度、体积小、功能强等特点, 体现了单片机发展的一种新趋势。PIC16F877A 是微芯公司采用14 位RISC 指令集的中级产品。该芯片内含A/D、内部EEPROM 存储器、比较输出、捕捉输入、PWM 输出、I2C 和SPI 接口、LCD 驱动、FLASH 程序存储器读写等功能, 应用十分广泛。 PIC16F877A 首先通过I2C 总线从模/数转换部分获取数据。这里采用了ADS1110 芯片进行A/D 转换。 ADS1110 是精密的连续自校准模/数(A/D) 转换器带有差分输入和高达16 位的分辨率封装为小型 SOT23 - 6。片内2.048V 的基准电压提供范围为± 2.048V 的输入差分电压。ADS1110 使用可兼容的I2C 串行接口在2.7V 至5.5V 的单电源下工作。ADS1110 可每秒采样15、30、60 或240 次以进行转换。片内可编程的增益放大器( PGA) 提供高达8 倍的增益, 并且允许以高分辨率对较小的信号进行测量。在单周期转换方式中ADS1110 在一次转换之后自动掉电在空闲期间极大地减少了电流消耗。ADS1110 的连接电路如图2 所示。图中RX 为待测电阻, R0 为标准电阻, 为了保证测量准确, 其上所加的2 伏电压是由10 伏精密电压基准芯片REF102 将输入24 伏电压转换为10 伏电压基准后, 再经过电阻分压和电压跟随器隔离后产生的, 电压十分的稳定。待测电阻RX 两端的电压再经过一个电压跟随器隔离, 如图3 上OP07 所示电路, 以防止电路右边的阻抗对测量的影响, 然后再经过一个一阶滤波后传输给了ADS1110, 这样就排除了外界对检测的干扰, 保证了待测电阻RX 两端电压稳定, A/D 转换的精度极高。 
3电阻分选仪系统组成及工作原理
本电阻分选仪系统功能由硬件和软件两大部分协调完成, 电阻分选仪硬件部分主要完成各个传感器信号的采集、转换, 电磁阀的动作, 数据的存储及各种信息的显示; 软件主要完成信号的处理和控制, 数据的管理等功能。软件方面首先由PIC 芯片的程序完成信号的转换和控制, 同时在C8051F022 芯片上移植入Small RTOS 嵌入式操作系统, 使其运行的迅速性、实时性和稳定性更高, 更好的进行数据的管理和存储。电阻分选仪整个系统的工作原理是首先将待测NTC 浸泡在油中来保持其恒温, 然后将其两端电压通过串行模/数转换器件ADS1110 转换成数字信号后传送给 PIC16F877A 单片机, 接着PIC16F877A 将所得的数值与先测得的标准电阻的数值相比较后进行分档, 再通过74LS595 移位寄存器输出控制电磁阀的动作, 从而将NTC 正确的分选出来。同时PIC16F877A 将分档值通过485 通讯传输给C8051F022 芯片。C8051F022 将数据实时的显示在液晶屏, 并把数据存入串行EEPROM 芯片24AA512 中, 操作人员随时可以用U 盘将数据拷走保存。C8051F022 也可以将输入的一些参数, 比如速度, 分档值等, 保存并传送给PIC16F877, 来控制它的运转。
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NTC Thermistor Sorter description
NTC negative temperature coefficient of the English abbreviation, the so-called NTC thermistor Sorter is the negative temperature coefficient thermistor. It is based on manganese, cobalt, nickel and copper and other metal oxides as the main material, made of ceramic manufacturing process. These metal oxide materials have semiconductor properties, because the way completely similar to the conductive germanium, silicon and other semiconductor materials. Low temperature, these oxides materials, carriers (electrons and cavities) the number of small, so its resistance value is higher; as the temperature increases, the number of carriers increased, so resistance value decreased. Advantage of this feature, NTC thermistor can be measured by its resistance value to determine the appropriate temperature, so as to achieve the purpose of detection and control of temperature. A different method of production processes, structure, shape, access to a wide range of NTC thermistors, which are widely used in temperature measurement, temperature compensation and other fields. NTC came out in the production, each change in the characteristics of resistance with temperature is not uniform, which need to NTC resistance changes according to different scope of sorting. The system PIC16F877A chip as the next position control NTC separation process, using 8-bit high-speed MCU C8051F022 upper machine as the core data management, serial EEPROM chip to record the data; and use CH375 chip will record data security and accurate to dump to the U disk, it can be convenient for data storage and management, and coupled with liquid crystal display, human-computer interaction more friendly. The instrument has a sorting accuracy, stable operation, easy to operate man-machine interface is friendly, easy management advantages.
1. Resistor sorter under position control module
PIC series of microcontrollers is introduced in the United States Microchip CMOS Microcontroller, the family reduced instruction set chip (RISC), Harvard bus architecture, 2-stage pipeline to take orders, with a practical, low-cost, instruction set is small, easy to learn, low-power, high speed, small size, functionality and other properties, reflect the development of a new trend microcontroller. PIC16F877A is the use of Microchips 14-bit RISC instruction set of the intermediate products. The chip includes A / D, the internal EEPROM memory, compare the output, capture input, PWM output, I2C and SPI interfaces, LCD driver, FLASH program memory read and write and other functions, is widely used. PIC16F877A first through the I2C bus from the A / D conversion part of the access to data. ADS1110 chip used here, A / D conversion. ADS1110 is a precision, continuously self-calibrating analog / digital (A / D) converter with differential inputs and up to 16 bits of resolution package for small SOT23 - 6. On-chip 2.048V reference voltage range of ± 2.048V to provide the input differential voltage. ADS1110 using the I2C-compatible serial interface at 2.7V to 5.5V single supply. ADS1110 can be 15,30,60 or 240 samples per second, times to be converted. On-chip programmable gain amplifier (PGA) gain of up to eight times, and allows high-resolution measurement of smaller signals. In the single-cycle conversion modes ADS1110 in a converted auto-power down during idle periods, after greatly reducing current consumption. ADS1110 connection circuit shown in Figure 2. RX diagram for the DUT resistance, R0 as a standard resistor, in order to ensure measurement accuracy, on which the increase of 2 volts from 10 volt precision voltage reference chip REF102 convert the input voltage of 24 V to 10 V voltage reference, after that, through the resistor divider and voltage follower arising after separation, the voltage is very stable. RX voltage across the resistor under test and then through a voltage follower isolation, as shown in Figure 3 on the OP07 circuit in order to prevent the right of the impedance of the circuit measuring the impact, and then filtered through a first-order transmitted to the ADS1110, so that exclude the interference of the outside world testing to ensure voltage stability across RX resistor under test, A / D conversion precision.
3 Resistance sorter system composition and working principle
The resistor sorter system function consists of hardware and software, coordinating the completion of two parts, resistor sorter hardware, some of the major individual sensor signals the completion of the acquisition, conversion, electromagnetic valve movement, data storage and display all kinds of information; software key the completion of signal processing and control, data management and other functions. Software, first of all procedures are completed by the PIC chip signal conversion and control, while C8051F022 chip implanted into Small RTOS embedded operating system to run as fast, real-time and stability of higher and better data for management and storage. Resistance Sorter works by the entire system under test NTC first immersed in oil to maintain its temperature, and then both ends of voltage through a serial A / D converter ADS1110 devices convert the digital signal transmitted to the PIC16F877A microcontroller then PIC16F877A values obtained for the first measured with the standard resistance values compared with after the sub-file, and then through the 74LS595 shift register output control solenoid valve action, thus sorting out the correct NTC. At the same time the value of PIC16F877A file will be transmitted through the 485 communications to the C8051F022 chip. C8051F022 data in real time displayed on the LCD screen, and the data into the serial EEPROM chip, 24AA512, the operator can readily use U disk to copy the data stored away. C8051F022 can also enter a number of parameters, such as speed, sub-file value, etc., save and send to the PIC16F877, to control its operation. For more please log on is to instrument network 010-63745117/63746117
