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本帖最后由 td456 于 2010-3-25 08:06 编辑
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1# 移民电工
( Y+ R* T, P! s7 U% vHart protocol is something between analog and digital,it is a digitally enhanced 4-20mA smart instrument communication.$ }) ^! C% B' P
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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"* ?; |. f% w. ~/ r" A" }8 A
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In DCS, HART is still treated as AI(Analog In) signal.3 C1 L- o% q4 a, h
Anyway it is only a transitional protocol and it is being replaced by Fieldbus or Profibus.
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8 f/ N" U. p1 s4 {. t+ nDevicenet is only a plant base network(底层网络). It deal with BYTE level information.; x$ D/ V1 Q6 r9 q9 O1 y8 B1 l
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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