BM00201-40型多路溫濕度變送器自動測量裝置的研制

秉(bing)承(cheng)“MEMS & MicSens”技術(shu)，淯源儀器近段時間一口氣推出(chu)了BM00201-40型(xing)溫濕(shi)度變送器巡(xun)檢儀、BM00101-2便攜(xie)式醫用(yong)輸液泵(beng)（注射泵(beng)）檢測儀、BM00301-（32-96）PCR儀溫度校(xiao)準儀、BM00401-8全站儀(yi)自動檢測儀(yi)四款小型儀(yi)器(qi)。這(zhe)四款儀(yi)器(qi)已(yi)經在(zai)諸多私人計量檢測(ce)公司得到應用(yong)。

BM00201-40型溫濕(shi)度變送器巡檢(jian)儀,可同時連接(jie)40臺溫(wen)濕(shi)度變(bian)送器（每臺待檢變(bian)送器由(you)一根(gen)獨立(li)的(de)易拔插信號線連接(jie)，防止連線出錯），自動完成(cheng)供電(dian)并有短(duan)路保(bao)護功能，自(zi)動讀取(qu)露點儀標準(zhun)值，10秒內完成40臺變送器的信號采集、數據處理、報表打印等工作。上位機應用軟件有各種參(can)數設置、數據自動計算、原始記(ji)錄查看、打印等(deng)功能。檢測流程(cheng)簡單，避免使用多種笨重(zhong)、復雜(za)的儀表，同時避免(mian)人工讀數、計算、記(ji)錄等(deng)低效(xiao)方(fang)式，從而大幅降低成本(ben)，效(xiao)率提高了10倍(bei)。

BM00201-40型(xing)溫(wen)濕度變送(song)器巡(xun)檢儀以其精密的(de)測量、便(bian)捷的(de)操作獲得成都(dou)計(ji)量院等省、市計(ji)量院青睞，下面四川淯源儀器詳細分析這(zhe)款儀器的研發。

 

引言(yan)

溫(wen)(wen)(wen)濕(shi)度(du)(du)變(bian)送(song)器(qi)(qi)(qi)(以下簡稱變(bian)送(song)器(qi)(qi)(qi))廣(guang)泛應用于工(gong)業(ye)生產、科學實驗(yan)、檢(jian)(jian)驗(yan)檢(jian)(jian)測、倉(cang)貯等作業(ye)環境的溫(wen)(wen)(wen)濕(shi)度(du)(du)測量(liang)(liang)。其(qi)輸(shu)出信(xin)(xin)號一般(ban)為(wei)(wei)(4～20)mA的直流信(xin)(xin)號或(0～l0)V的電壓(ya)(ya)信(xin)(xin)號。變(bian)送(song)器(qi)(qi)(qi)校準(zhun)采用高(gao)精(jing)度(du)(du)溫(wen)(wen)(wen)濕(shi)度(du)(du)校驗(yan)箱或發(fa)生器(qi)(qi)(qi)作為(wei)(wei)溫(wen)(wen)(wen)、濕(shi)度(du)(du)源(yuan)，采用精(jing)密露點儀(yi)為(wei)(wei)標(biao)準(zhun)器(qi)(qi)(qi)，校準(zhun)時(shi)，首先需要對其(qi)施加(jia)24V直流電源(yuan)，然后用高(gao)精(jing)度(du)(du)電壓(ya)(ya)或電流表測量(liang)(liang)其(qi)信(xin)(xin)號值，再由(you)人工(gong)計(ji)算和(he)記錄溫(wen)(wen)(wen)濕(shi)度(du)(du)數據。一次(ci)只(zhi)能測量(liang)(liang)一路信(xin)(xin)號，每(mei)次(ci)人工(gong)切換檢(jian)(jian)測信(xin)(xin)號都要重新連接(jie)儀(yi)表。當(dang)被檢(jian)(jian)變(bian)送(song)器(qi)(qi)(qi)較(jiao)多時(shi)，測量(liang)(liang)過(guo)程(cheng)非常(chang)繁瑣，加(jia)上大量(liang)(liang)的讀(du)數和(he)計(ji)算過(guo)程(cheng)，使校準(zhun)工(gong)作效率低、成(cheng)本(ben)高(gao)、勞動強度(du)(du)大。為(wei)(wei)此，研制一體(ti)化多路溫(wen)(wen)(wen)濕(shi)度(du)(du)變(bian)送(song)器(qi)(qi)(qi)測量(liang)(liang)裝置。

 

1 系統工作原理(li)

 

系統工作原(yuan)理(li)(li)如圖1所示(shi)。系統以(yi)ARM為核心。ARM控(kong)制(zhi)(zhi)變送器(qi)電源(yuan)導通(tong)(tong)(tong)后(hou)，根據其輸(shu)出信號(hao)類(lei)型自(zi)動(dong)將信號(hao)切換到相(xiang)應(ying)的(de)信號(hao)調理(li)(li)電路(lu)，模(mo)(mo)擬開關在ARM的(de)控(kong)制(zhi)(zhi)下(xia)將信號(hao)輸(shu)入A／D轉換器(qi)，將模(mo)(mo)擬信號(hao)轉換為數字(zi)信號(hao)，再通(tong)(tong)(tong)過(guo)無線模(mo)(mo)塊上傳至上位機(ji)處理(li)(li)。此外，ARM控(kong)制(zhi)(zhi)RS232和(he)I2C接口分別(bie)與露點儀和(he)EEPROM通(tong)(tong)(tong)信。上位機(ji)控(kong)制(zhi)(zhi)軟件基于可視化編程軟件Labview，實(shi)現數據的(de)讀取、計(ji)算、保存、顯示(shi)，以(yi)及(ji)原(yuan)始記錄自(zi)動(dong)生成等功能(neng)。

 

2 硬件電路設計

硬件電路(lu)主要包括：信號調(diao)理電路(lu)、模擬開(kai)關、A／D轉換(huan)器、ARM控制器、無(wu)線模塊、EEPROM、電源模塊等。

2．1 ARM控制器

ARM 控制器選用意法半導體公司生產的STM32F103C8，該處理器基于高性能的32位ARM Cortex—M3內核，高(gao)頻率達72MHz，內置64K FLASH 和20KSRAM。利用其豐富的接口實現對電源、信號類型切換、模擬開關、A／D轉換器的控制，以及同露點儀、上位機的通信。

2．2 信號(hao)調理電路

變(bian)送器(qi)(qi)輸(shu)(shu)出(chu)信(xin)(xin)號類型(xing)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)兩種，為(wei)(wei)了將變(bian)送器(qi)(qi)信(xin)(xin)號調整(zheng)到A／D轉換器(qi)(qi)的(de)輸(shu)(shu)入(ru)范(fan)圍，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)信(xin)(xin)號通過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)分壓(ya)(ya)，使其(qi)降到(0～5)V，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流信(xin)(xin)號通過(guo)取樣電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)使其(qi)變(bian)為(wei)(wei)(1～5)V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)信(xin)(xin)號。調整(zheng)后的(de)信(xin)(xin)號再由電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)跟隨器(qi)(qi)輸(shu)(shu)出(chu)至模(mo)擬開關。ARM通過(guo)控制繼(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)切(qie)換電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流或電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)調理電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，如圖(tu)2所示(shi)(shi)。為(wei)(wei)了控制34路(lu)(lu)繼(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)開關，系(xi)統采用74HC595移位寄(ji)(ji)存器(qi)(qi)作為(wei)(wei)驅動(dong)器(qi)(qi)。該芯(xin)片具有8位鎖存、8位串(chuan)行(xing)(xing)輸(shu)(shu)入(ru)、8位串(chuan)／并行(xing)(xing)輸(shu)(shu)出(chu)、串(chuan)／并移位寄(ji)(ji)存器(qi)(qi)和三態輸(shu)(shu)出(chu)等(deng)功能。8位并行(xing)(xing)輸(shu)(shu)出(chu)端可分別控制8路(lu)(lu)繼(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)，因此(ci)，系(xi)統共(gong)需要5片74HC595。如圖(tu)3所示(shi)(shi)，并行(xing)(xing)輸(shu)(shu)出(chu)端Q0～Q7同三極(ji)管B極(ji)連(lian)接，當輸(shu)(shu)出(chu)端為(wei)(wei)高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)平時繼(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)吸(xi)合，此(ci)時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)信(xin)(xin)號檢測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，反之為(wei)(wei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流信(xin)(xin)號檢測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。串(chuan)行(xing)(xing)數據輸(shu)(shu)入(ru)端Ds接收ARM發(fa)出(chu)的(de)串(chuan)行(xing)(xing)數據，Q7一連(lian)接下級的(de)Ds端，依次傳遞串(chuan)行(xing)(xing)數據。

 

2．3 模擬(ni)開關

模(mo)擬開(kai)(kai)關具有體積小(xiao)、速度快、功耗(hao)小(xiao)、無抖動等(deng)特點，在(zai)多(duo)路信號(hao)采集(ji)系統(tong)中有廣泛(fan)應用。本系統(tong)采用ADI公司的16選(xuan)I CMOS模(mo)擬開(kai)(kai)關ADG706。該芯(xin)片導通電(dian)阻為2．5Q，開(kai)(kai)關時間(jian)40ns，大輸入電(dian)壓5．5V。34路變送器共有68通道(dao)信號(hao)，因此需要5片ADG706。系

統工(gong)作時，ARM控制(zhi)模擬開(kai)關的地址選(xuan)通端和(he)輸出(chu)使能端，輸出(chu)需要檢(jian)測的信號(hao)。

2．4 A／D轉(zhuan)換(huan)器(qi)

采用TI公司生產的(de)高性能(neng)A／D轉換器(qi)ADS1256。其主要特點有(you)(you)：24位無(wu)(wu)數據丟失；非線(xian)性度：0．0010％ ；高達23比特的(de)無(wu)(wu)噪聲精度；數據采樣率可達30ksps；帶(dai)有(you)(you)模擬多(duo)路開(kai)關(guan)(MUX)；可配(pei)置為8路單極(ji)輸入或4路差動(dong)輸入；具有(you)(you)自校準(zhun)和系統校準(zhun)；帶(dai)有(you)(you)串行外設接口

(SPI)等(deng)。ADS1256提(ti)供(gong)了8路模(mo)擬輸(shu)入(ru)(ru)(ru)端，可使用(yong)模(mo)擬多路開(kai)關(guan)(MUX)寄存器(qi)來將其配置為(wei)四路差(cha)動(dong)輸(shu)入(ru)(ru)(ru)、八(ba)路單(dan)極(ji)(ji)輸(shu)入(ru)(ru)(ru)或差(cha)動(dong)輸(shu)入(ru)(ru)(ru)和(he)單(dan)極(ji)(ji)輸(shu)入(ru)(ru)(ru)的(de)(de)組合(he)。系(xi)統采用(yong)5路單(dan)極(ji)(ji)輸(shu)入(ru)(ru)(ru)i貝0量，將AIN0～AIN4作(zuo)為(wei)單(dan)極(ji)(ji)輸(shu)入(ru)(ru)(ru)端，AINCOM作(zuo)為(wei)公共輸(shu)人端。而未用(yong)的(de)(de)模(mo)擬輸(shu)入(ru)(ru)(ru)引(yin)腳懸空，這樣有

利(li)于減小輸(shu)人泄(xie)漏電(dian)流(liu)。ADS1256的主時鐘由一(yi)個7．68MHz外部(bu)晶(jing)振提供。在(zai)模擬(ni)電(dian)源和數(shu)字電(dian)源的輸(shu)入(ru)端并(bing)聯一(yi)個小的陶瓷電(dian)容(rong)和一(yi)個大的鉭電(dian)容(rong)。ADS1256外圍電(dian)路如圖4所示。

 

2．5 變(bian)送器電源控制

變(bian)(bian)送器(qi)電源(yuan)(yuan)(yuan)一(yi)般為12～24VDC，要求每路(lu)(lu)電源(yuan)(yuan)(yuan)獨立可(ke)控(kong)且文(wen)波小于1％ 。因此，需要設計34路(lu)(lu)24V電源(yuan)(yuan)(yuan)。24V電源(yuan)(yuan)(yuan)由外接(jie)的(de)開關(guan)電源(yuan)(yuan)(yuan)提供，以34路(lu)(lu)達(da)林(lin)頓(dun)管(guan)作(zuo)為每路(lu)(lu)電源(yuan)(yuan)(yuan)的(de)開關(guan)。ARM控(kong)制達(da)林(lin)頓(dun)管(guan)就可(ke)控(kong)制變(bian)(bian)送器(qi)電源(yuan)(yuan)(yuan)。為減少干擾，輸出電壓經過LC濾波。為防止短路(lu)(lu)等情(qing)況，每路(lu)(lu)電源(yuan)(yuan)(yuan)增加可(ke)恢(hui)復(fu)保險絲。變(bian)(bian)送器(qi)控(kong)制電源(yuan)(yuan)(yuan)電路(lu)(lu)如圖(tu)5所示。

 

2．6 無線模塊

采(cai)用深(shen)圳(zhen)市安美通科技有(you)限公司(si)生產的(de)(de)APC320無線數據傳(chuan)輸(shu)模塊(kuai)。它嵌入(ru)了(le)高速低功耗單(dan)片機和高性能(neng)射(she)頻芯片SI4463，創新的(de)(de)采(cai)用高效的(de)(de)循環交織(zhi)糾(jiu)錯編碼，抗干(gan)擾能(neng)力(li)和靈敏度都大大提高。APC320模塊(kuai)工作電壓(ya)為2．1～3．6V，在接收(shou)狀態下電流僅(jin)15mA。

2．7 EEPROM

EEPROM用(yong)于(yu)存(cun)儲自動校準數據。采(cai)用(yong)ATMEL公司生產的AT24C512。該存(cun)儲器特點：64KB容量，I2C串行(xing)總線，16 位地址，100000 次編程／擦寫周期(qi)。AT24C512外(wai)圍電(dian)路(lu)如圖所(suo)示(shi)：A0一A2接(jie)地設置(zhi)存(cun)儲器地址為0，WP接(jie)地設置(zhi)為可讀寫，SCL和SDA接(jie)上(shang)拉電(dian)阻。外(wai)圍電(dian)路(lu)如圖6所(suo)示(shi)。

 

 

3 上位機設計

上位機(ji)控(kong)制(zhi)軟(ruan)件基(ji)于Labview和Access2007數(shu)據庫開發(fa)，實現系統(tong)管理與控(kong)制(zhi)、變送器數(shu)據采集、顯示、運(yun)算處理、存儲、數(shu)據查詢和自(zi)動生成word測試報(bao)告等功(gong)能。

 

4 結論

經測(ce)試(shi)，本裝置電(dian)壓測(ce)量(liang)范圍(wei)：0—10V；分辨率：0．1mV；大允(yun)許誤差：0．05％ ；電(dian)流(liu)測(ce)量(liang)范圍(wei)：0～20mA；分辨率：0．1uA；大允(yun)許誤差：0．05％。可同(tong)時滿足34臺變送(song)器即(ji)64路電(dian)信號的自動測(ce)量(liang)。具有操作簡(jian)單、效率高、成本低、智(zhi)能化程度高等特點，非常適合多臺溫濕度變送(song)器校準(zhun)工作。

 

參考文(wen)獻(xian)

[1]康赫男．溫(wen)濕度變送器輸出參數的校準方法[J]．計量與測試技術，2011(08)．

[2]梅榮(rong)．基于(yu)單片機(ji)的溫濕度(du)檢測與(yu)控(kong)制系(xi)統研(yan)究[J]．農機(ji)化研(yan)究，2012(01)．

[3]彭剛，春(chun)志強(qiang)．基于ARM Cortex—M3的STM32系列(lie)嵌入式微控制器應(ying)用實踐[M]．北(bei)京(jing)：電子工業出(chu)版社，2011．

 

作者簡介：曾博才(cai)，男，工程(cheng)師，碩士。工作單(dan)位：四川淯源儀器有限公司。