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本帖最后由 td456 于 2010-3-25 08:06 编辑 2 j/ p; X, n' a! Z$ F5 F3 t
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Hart protocol is something between analog and digital,it is a digitally enhanced 4-20mA smart instrument communication.% ^6 z" I H( \, e
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"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.1 N3 c Z4 a/ g* x4 }: ~2 r
Anyway it is only a transitional protocol and it is being replaced by Fieldbus or Profibus.2 \2 ^# H* {/ a0 w; v0 H4 H
% A7 r, {- e9 f$ N3 r0 pDevicenet is only a plant base network(底层网络). It deal with BYTE level information.
/ {. o' p' d) x; f: dDevicenet 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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发表于 2010-3-24 22:43
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