m340 plc和編碼器串行rs485通信采用modbus rtu通信規(guī)約，這個通訊協(xié)議已廣泛被國內(nèi)外各行業(yè)作為系統(tǒng)集成的一種通用工業(yè)標(biāo)準協(xié)議，有利于系統(tǒng)的維護和擴展。plc為主站，編碼器為從站。

　　查編碼器技術(shù)手冊，水位測值的modbus地址是4x0000，根據(jù)modbus通信規(guī)約信息幀結(jié)構(gòu)讀取地址 1 傳感器的水位測量值，應(yīng)發(fā)送以下通信碼：m340 plc讀取水位信息主要用read_var功能模塊：140CRA21110分布式I/O  

廈門仲鑫達自動化設(shè)備有限公司

：李素云

企業(yè)QQ：，2851195466

手機：

：

　　01 03 0000 0001 840a

　　站地址 　功能碼 　　首地址 　　個數(shù)　　 crc校驗碼

　　功能模塊說明[1]

　　adr

　　通信地址：語法為 addm (`r.m.c.node`機架號.模塊號.通道號.站地址) 類型。

　　obj 要讀取的對象類型

　　’%m’：內(nèi)部位

　　’%mw’：內(nèi)部字

　　’%s’：系統(tǒng)位

　　’%sw’：系統(tǒng)字

　　num 讀取的個對象的索引。

　　nb 要讀取的對象的數(shù)量。

　　recp輸出參數(shù)包含所讀取對象的值的字表。

　　gest交換管理表：4個字的數(shù)組。

　　表1 交換管理表

Omega FMA5416ST Gas Mass Flow Controller, Gas: N2, Max Gas Pressure: 500psi

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　　New In Box Pentair SF0524414 Filter Fan, Power: 24VDC 0.17A, Speed: 3050RPM