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本帖最后由 td456 于 2010-3-25 08:06 编辑 2 Q( [# [5 x9 k. m |0 Q7 m/ _( c2 ?
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1# 移民电工
1 G4 [3 C, M8 DHart protocol is something between analog and digital,it is a digitally enhanced 4-20mA smart instrument communication.- c( h: z: J8 }4 o0 X
/ ]# m9 O% d( g; j"The HART protocol makes use of the Bell 202 Frequency Shift Keying (FSK) standard to superimpose digital communication signals at a low level on top of the 4-20 mA. Since the digital FSK signal is phase continuous, it does not interfere with the 4-20 mA signal. A logical “1” is represented by a frequency of 1200 Hz and a logical “0” is represented by a frequency of 2200 Hz"
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In DCS, HART is still treated as AI(Analog In) signal.
7 a& b/ H1 {( P6 N/ L- ZAnyway it is only a transitional protocol and it is being replaced by Fieldbus or Profibus.
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! A; \3 u# u- D1 k; g; v; c. O4 k7 pDevicenet is only a plant base network(底层网络). It deal with BYTE level information.8 Q% H* a+ p% N% {8 b3 A
Devicenet can not be a backbone of a plant network but Fieldbus can. There is difference between Devicenet and Fieldbus. They deal with difference level of communication. |
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