業機械方面(mian)的教學與研(yan)究。

　　型熱(re)電(dian)(dian)(dian)偶(ou)(ou)的(de)精(jing)度(du)(du)分為(wei)三(san)級(ji)：I級(ji)：測溫(wen)(wen)范(fan)圍01000C，誤差1.5C，為(wei)測量溫(wen)(wen)度(du)(du)的(de)0.4%：圖i系(xi)統硬件結構框圖K型熱(re)電(dian)(dian)(dian)偶(ou)(ou)材料性(xing)能指標(biao)：正級(ji)為(wei)鎳(nie)硅，負(fu)極為(wei)鎳(nie)鋁，正極和負(fu)極熔點分別(bie)為(wei)1427°C和1399C；電(dian)(dian)(dian)阻率（0C）分別(bie)為(wei)70.6D/cni和29.4nD/cni，熱(re)膨脹系(xi)數(shu)分別(bie)為(wei)13.1xl-6時(shi)的(de)熱(re)導率分別(bie)為(wei)655Mpa和586Mpa.由于熱(re)電(dian)(dian)(dian)偶(ou)(ou)的(de)輸(shu)(shu)出(chu)靈(ling)敏度(du)(du)很低，每(mei)°<：只(zhi)有幾(ji)十pV的(de)電(dian)(dian)(dian)壓輸(shu)(shu)出(chu)，故要求放大電(dian)(dian)(dian)路的(de)溫(wen)(wen)漂必須很小，另外熱(re)電(dian)(dian)(dian)偶(ou)(ou)都具(ju)有非(fei)線性(xing)誤差，這就要求有非(fei)線性(xing)校正電(dian)(dian)(dian)路，同時(shi)還需考慮冷端補償。

　　2.1.1冷端補(bu)(bu)償(chang)和(he)放(fang)(fang)大(da)(da)(da)電(dian)路(lu)(lu)K型熱(re)(re)電(dian)偶(ou)的(de)(de)(de)(de)(de)(de)函(han)數(shu)(shu)(shu)(shu)的(de)(de)(de)(de)(de)(de)形式(shi)(shi)為(wei)(wei)：+上(shang)指數(shu)(shu)(shu)(shu)表達式(shi)(shi)的(de)(de)(de)(de)(de)(de)有(you)(you)關系(xi)數(shu)(shu)(shu)(shu)，此(ci)函(han)數(shu)(shu)(shu)(shu)覆蓋(gai)C1372C溫區，由(you)上(shang)式(shi)(shi)可(ke)看出(chu)(chu)(chu)熱(re)(re)電(dian)偶(ou)的(de)(de)(de)(de)(de)(de)熱(re)(re)電(dian)勢輸(shu)(shu)(shu)出(chu)(chu)(chu)數(shu)(shu)(shu)(shu)值較小(xiao)且和(he)溫度(du)(du)之間的(de)(de)(de)(de)(de)(de)關系(xi)為(wei)(wei)非(fei)(fei)線(xian)性(xing)(xing)(xing)：同(tong)時(shi)熱(re)(re)電(dian)偶(ou)測溫時(shi)還要(yao)(yao)(yao)求(qiu)冷端保持為(wei)(wei)（冰(bing)點(dian)），否則(ze)會(hui)帶(dai)(dai)來較大(da)(da)(da)的(de)(de)(de)(de)(de)(de)誤差，但這給(gei)使(shi)用(yong)(yong)帶(dai)(dai)來很大(da)(da)(da)的(de)(de)(de)(de)(de)(de)不便，因此(ci)，為(wei)(wei)解決上(shang)述問題在這里選用(yong)(yong)了(le)一(yi)(yi)片(pian)(pian)(pian)美(mei)國(guo)(guo)（AnalogDevicesInc）生產的(de)(de)(de)(de)(de)(de)帶(dai)(dai)冷端補(bu)(bu)償(chang)的(de)(de)(de)(de)(de)(de)單(dan)片(pian)(pian)(pian)熱(re)(re)電(dian)偶(ou)放(fang)(fang)大(da)(da)(da)器(qi)集(ji)成芯片(pian)(pian)(pian)AD595，該芯片(pian)(pian)(pian)的(de)(de)(de)(de)(de)(de)特點(dian)如下(xia)：低陰抗(kang)電(dian)壓輸(shu)(shu)(shu)出(chu)(chu)(chu)，10mV/C，即將(jiang)非(fei)(fei)線(xian)性(xing)(xing)(xing)的(de)(de)(de)(de)(de)(de)熱(re)(re)電(dian)勢輪(lun)換(huan)(huan)(huan)為(wei)(wei)線(xian)性(xing)(xing)(xing)電(dian)壓輸(shu)(shu)(shu)出(chu)(chu)(chu)，具(ju)有(you)(you)片(pian)(pian)(pian)內(nei)冰(bing)點(dian)補(bu)(bu)償(chang)電(dian)路(lu)(lu)，具(ju)有(you)(you)斷偶(ou)報警(jing)功(gong)能(neng)，K型熱(re)(re)電(dian)偶(ou)電(dian)動勢經(jing)AD595放(fang)(fang)大(da)(da)(da)后其(qi)輸(shu)(shu)(shu)出(chu)(chu)(chu)電(dian)壓為(wei)(wei)：根(gen)據上(shang)式(shi)(shi)由(you)熱(re)(re)電(dian)偶(ou)的(de)(de)(de)(de)(de)(de)分度(du)(du)表即可(ke)得到(dao)10mV/C的(de)(de)(de)(de)(de)(de)電(dian)壓輸(shu)(shu)(shu)出(chu)(chu)(chu)。由(you)AD595構(gou)成的(de)(de)(de)(de)(de)(de)正負電(dian)源(yuan)熱(re)(re)電(dian)偶(ou)放(fang)(fang)大(da)(da)(da)電(dian)路(lu)(lu)如所示為(wei)(wei)滿足本(ben)系(xi)統(tong)控溫精度(du)(du)的(de)(de)(de)(de)(de)(de)要(yao)(yao)(yao)求(qiu)，本(ben)系(xi)統(tong)選用(yong)(yong)較高(gao)辯(bian)率(lv)的(de)(de)(de)(de)(de)(de)美(mei)國(guo)(guo)MAXIM公司12位(wei)的(de)(de)(de)(de)(de)(de)串(chuan)行(xing)A/D轉(zhuan)換(huan)(huan)(huan)器(qi)MAX171.MAX171是帶(dai)(dai)光電(dian)隔(ge)離的(de)(de)(de)(de)(de)(de)串(chuan)行(xing)輸(shu)(shu)(shu)出(chu)(chu)(chu)12位(wei)ADC，其(qi)內(nei)部(bu)具(ju)有(you)(you)一(yi)(yi)個12位(wei)ADC，一(yi)(yi)個低漂移掩埋式(shi)(shi)齊(qi)納電(dian)壓基準源(yuan)和(he)三個光電(dian)耦合器(qi)，因此(ci)該芯片(pian)(pian)(pian)在其(qi)模擬輸(shu)(shu)(shu)入和(he)數(shu)(shu)(shu)(shu)字(zi)接(jie)口(kou)之間實現(xian)了(le)電(dian)氣(qi)隔(ge)離，其(qi)隔(ge)離電(dian)壓超(chao)過1500V，因此(ci)大(da)(da)(da)大(da)(da)(da)提(ti)高(gao)了(le)數(shu)(shu)(shu)(shu)據采(cai)集(ji)的(de)(de)(de)(de)(de)(de)安全性(xing)(xing)(xing)和(he)可(ke)靠性(xing)(xing)(xing)。MAX171的(de)(de)(de)(de)(de)(de)主要(yao)(yao)(yao)特性(xing)(xing)(xing)及技術指標如下(xia)：分辨率(lv)12位(wei)轉(zhuan)換(huan)(huan)(huan)時(shi)間5-8nS輸(shu)(shu)(shu)出(chu)(chu)(chu)方式(shi)(shi)串(chuan)行(xing)非(fei)(fei)線(xian)性(xing)(xing)(xing)誤差1LSB檢測通道電(dian)路(lu)(lu)原理(li)圖采(cai)用(yong)(yong)串(chuan)行(xing)式(shi)(shi)A/D轉(zhuan)換(huan)(huan)(huan)器(qi)可(ke)使(shi)單(dan)片(pian)(pian)(pian)機(ji)工作于內(nei)總(zong)線(xian)方式(shi)(shi)，而無需擴(kuo)展外部(bu)三總(zong)線(xian)結構(gou)，這可(ke)大(da)(da)(da)大(da)(da)(da)簡(jian)化單(dan)片(pian)(pian)(pian)機(ji)應用(yong)(yong)系(xi)統(tong)設計(ji)，同(tong)時(shi)又提(ti)高(gao)了(le)系(xi)統(tong)可(ke)靠性(xing)(xing)(xing)。MAX171和(he)單(dan)片(pian)(pian)(pian)機(ji)的(de)(de)(de)(de)(de)(de)接(jie)口(kou)電(dian)路(lu)(lu)如圖二所示。

　　MAX171模擬電(dian)(dian)壓(ya)(ya)輸(shu)入范圍為(wei)(wei)0-5V而AD595的電(dian)(dian)壓(ya)(ya)輸(shu)出為(wei)(wei)10mV/C，其滿刻度輸(shu)出電(dian)(dian)壓(ya)(ya)（1200C）為(wei)(wei)10mVxl200=12V，己遠遠超(chao)出A/D轉(zhuan)換器的電(dian)(dian)壓(ya)(ya)輸(shu)入范圍，故需采用電(dian)(dian)阻分(fen)壓(ya)(ya)電(dian)(dian)路(lu)進行分(fen)壓(ya)(ya)。本設(she)計中由R，和R2組成(cheng)分(fen)壓(ya)(ya)器電(dian)(dian)路(lu)。1=7=51當溫度為(wei)(wei)1200C時，輸(shu)出電(dian)(dian)壓(ya)(ya)為(wei)(wei)VQ1=V.R2/（R，+R2）=5V，可滿足A/D轉(zhuan)換器模擬輸(shu)入電(dian)(dian)壓(ya)(ya)要求（0-5V）。

　　MAX171和單(dan)(dan)片機可直(zhi)接接口，前(qian)提是(shi)MAX171時鐘頻率必需低于1MHZ，本系統中(zhong)MAX171的(de)輸出信(xin)號(hao)(hao)直(zhi)接接到AT89C5〗單(dan)(dan)片機的(de)RXD端，同時TXD端則(ze)為MAX171提供(gong)時鐘信(xin)號(hao)(hao)，可見MAX171時鐘信(xin)號(hao)(hao)是(shi)由單(dan)(dan)片機提供(gong)的(de)，單(dan)(dan)片機利(li)用其(qi)串(chuan)行(xing)口與(yu)A/D轉(zhuan)換器(qi)(qi)通(tong)信(xin)，將(jiang)串(chuan)口設置為工作方式(shi)0，即(ji)同步移(yi)位寄存器(qi)(qi)方式(shi)，此方式(shi)下RXD用于接收數(shu)據(ju)，TXD輸出同步脈沖。一次(ci)A/D轉(zhuan)換結(jie)果(guo)(guo)分(fen)兩次(ci)計(ji)讀入(ru)到單(dan)(dan)片機中(zhong)，再合成12位A/D轉(zhuan)換結(jie)果(guo)(guo)。

　　本系統(tong)單(dan)片機的(de)(de)晶振頻率并選為12MHZ，則串行(xing)工(gong)作方式0的(de)(de)波待率固定為f；se/12=lMHZ，可滿(man)足MAX171對時鐘頻率的(de)(de)要求(qiu)。

　　2.2控(kong)制(zhi)通道本(ben)設(she)計選(xuan)用(yong)過零(ling)觸發(fa)固態繼電(dian)器為主控(kong)制(zhi)元件，用(yong)以控(kong)制(zhi)電(dian)阻(zu)爐的加溫與斷開。

　　固(gu)(gu)態(tai)繼(ji)電器(qi)特點如下(xia)：1控(kong)制電壓(ya)低（314V），驅動電流小（315mA）；2輸(shu)(shu)入(ru)控(kong)制電壓(ya)與TTL、CMOS電平兼容；3輸(shu)(shu)出與輸(shu)(shu)入(ru)間采用光電隔離；4輸(shu)(shu)出無(wu)觸(chu)(chu)點、無(wu)噪音、無(wu)火花，開關頻率高，固(gu)(gu)態(tai)繼(ji)電器(qi)可由單(dan)片機的(de)P27口通過TTL反相器(qi)直接驅動，采用過零觸(chu)(chu)發(fa)方式即(ji)改變(bian)一個(ge)溫(wen)度控(kong)制周期(qi)內(nei)施(shi)加(jia)到電阻(zu)爐正弦波的(de)個(ge)數(shu)，即(ji)可改變(bian)電阻(zu)爐輸(shu)(shu)入(ru)的(de)平均(jun)功率，從而達到控(kong)溫(wen)的(de)目的(de)，同時過零觸(chu)(chu)發(fa)避免波形非正弦而對電網造(zao)成的(de)公害。

　　固(gu)態繼電(dian)器(qi)的選用(yong)需滿(man)足固(gu)態繼電(dian)器(qi)Ul.2倍電(dian)源電(dian)壓。

　　固態繼電(dian)器IN21.5倍(bei)電(dian)阻爐(lu)額定電(dian)流。

　　2.3單(dan)片(pian)機(ji)(ji)應用(yong)(yong)系統單(dan)片(pian)機(ji)(ji)選用(yong)(yong)ATMEL公司AT89C52，該單(dan)片(pian)機(ji)(ji)屬MCS-51系列(lie)，因其(qi)內部含有8K字節Flash程序(xu)存儲(chu)器(qi)，故勿(wu)需外擴程序(xu)存儲(chu)器(qi)，由于(yu)本(ben)(ben)系統的(de)A/D轉換(huan)器(qi)采(cai)用(yong)(yong)串行(xing)(xing)結構也無需總(zong)線擴展(zhan)，故本(ben)(ben)單(dan)片(pian)機(ji)(ji)系統為內總(zong)線單(dan)片(pian)機(ji)(ji)系統，該設計(ji)(ji)方(fang)法符合近(jin)年來單(dan)片(pian)機(ji)(ji)設計(ji)(ji)單(dan)片(pian)化(hua)的(de)設計(ji)(ji)思想，使(shi)系統結構大(da)為簡化(hua)，同時(shi)可(ke)靠性也大(da)為提(ti)高(gao)。單(dan)片(pian)機(ji)(ji)的(de)硬件資源(yuan)也可(ke)全部提(ti)供給(gei)本(ben)(ben)系統使(shi)用(yong)(yong)，單(dan)片(pian)機(ji)(ji)的(de)P.口(kou)、P2口(kou)可(ke)做為通用(yong)(yong)I/O使(shi)用(yong)(yong)。系統配有25鍵小鍵盤，其(qi)中0-F十六個(ge)(ge)數(shu)字鍵和(he)八個(ge)(ge)功能鍵，一個(ge)(ge)REST鍵，由P，口(kou)構成(cheng)矩陣鍵盤，用(yong)(yong)于(yu)輸入(ru)控(kong)制算(suan)(suan)法的(de)參數(shu)及加(jia)熱方(fang)式曲(qu)線，由MC14489顯示(shi)驅(qu)動芯片(pian)構成(cheng)5位串行(xing)(xing)顯示(shi)器(qi)用(yong)(yong)于(yu)顯示(shi)輸入(ru)參數(shu)和(he)實(shi)際溫度值(zhi)，蜂鳴(ming)器(qi)用(yong)(yong)于(yu)加(jia)熱結束(shu)時(shi)的(de)聲音提(ti)示(shi)，E2PROM用(yong)(yong)于(yu)保存控(kong)制算(suan)(suan)法參數(shu)和(he)工藝曲(qu)線參數(shu)。

　　3控制算(suan)法電(dian)阻爐(lu)是一(yi)個純(chun)滯(zhi)后(hou)的一(yi)階大(da)慣性環(huan)節，其傳遞函(han)數為Wd（S）=KdeA/（TdS+l），其中對(dui)(dui)象時(shi)(shi)間常(chang)數Td=90mim純(chun)滯(zhi)后(hou)時(shi)(shi)間e=5min，廣義被控對(dui)(dui)象放大(da)系數反〗。

　　考慮到被控對象模(mo)型的(de)不精確(que)性和其(qi)參數(shu)隨時(shi)間(jian)(jian)的(de)漂移(yi)以及(ji)系(xi)統要(yao)求超調量小而允(yun)許調節(jie)時(shi)間(jian)(jian)過程(cheng)長(chang)，控制器的(de)控制算(suan)(suan)式(shi)可采用(yong)帶積(ji)分分離的(de)PID方式(shi)或大林算(suan)(suan)法。

　　采(cai)(cai)(cai)用(yong)大林(lin)算法時(shi)，其(qi)相應的(de)(de)數(shu)(shu)字控制器的(de)(de)Z傳遞函數(shu)(shu)為(wei)(wei)其(qi)中Td為(wei)(wei)閉環系(xi)統(tong)(tong)時(shi)間(jian)(jian)常數(shu)(shu)，T為(wei)(wei)采(cai)(cai)(cai)樣(yang)周(zhou)期(qi)，N為(wei)(wei)純滯(zhi)后(hou)時(shi)間(jian)(jian)G與采(cai)(cai)(cai)樣(yang)周(zhou)期(qi)間(jian)(jian)的(de)(de)整(zheng)數(shu)(shu)倍數(shu)(shu)（0=NTN取整(zheng)數(shu)(shu)）對上式(shi)進行Z為(wei)(wei)提高(gao)控溫精(jing)度在升溫或降溫過(guo)程中當(dang)溫度偏(pian)差值大于(yu)5%時(shi)，自動(dong)調用(yong)PID算式(shi)：4系(xi)統(tong)(tong)軟件應用(yong)軟件由主程序(xu)(xu)Ta中斷服務程序(xu)(xu)、鍵輸入掃(sao)描程序(xu)(xu)及增(zeng)量式(shi)PID運算模(mo)塊(kuai)與大林(lin)運算模(mo)塊(kuai)等(deng)組成。主程序(xu)(xu)框圖見(jian)，其(qi)它程序(xu)(xu)從略(lve)。

　　5結束語本(ben)裝置具(ju)有較篼的控溫(wen)精度(du)同時可(ke)根據加(jia)熱特性(xing)曲線(xian)完成二個(ge)熱處理(li)加(jia)工(gong)生產周期，可(ke)取代(dai)現有的常(chang)規(gui)儀表接觸(chu)器控溫(wen)方式，因而具(ju)有較高(gao)的應用價(jia)值。