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本帖最后由 td456 于 2010-3-25 08:06 编辑 ( l7 N: b8 t# N0 S# M0 g
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1# 移民电工
( ?$ D5 Y5 W6 Y, H( ZHart protocol is something between analog and digital,it is a digitally enhanced 4-20mA smart instrument communication.) O$ _& E/ D& l% |: m3 Z! R
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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". K' F& B' n/ a; D8 o. x
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In DCS, HART is still treated as AI(Analog In) signal.
+ s! I& t% a6 VAnyway it is only a transitional protocol and it is being replaced by Fieldbus or Profibus.; }; G" O! U7 Z# j
' t, H; O# H$ ^" p1 Q5 u! cDevicenet is only a plant base network(底层网络). It deal with BYTE level information.& N8 P9 k9 V4 F4 z! C' Q" |- R
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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