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本帖最后由 td456 于 2010-3-25 08:06 编辑
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. N A% c* E' S7 ]# Z$ q! X' ~, U 1# 移民电工 " d- S Z+ t. N6 e' q5 P, T
Hart protocol is something between analog and digital,it is a digitally enhanced 4-20mA smart instrument communication.1 b- G( [2 \/ _; ]
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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"9 k6 |1 g/ m$ [ t" V* ^
* ?" s& k, K' T+ t% h* `* d* `) c, \; |/ aIn DCS, HART is still treated as AI(Analog In) signal.
4 F8 D% i2 a) {2 }& b8 G% s" a4 ZAnyway it is only a transitional protocol and it is being replaced by Fieldbus or Profibus.2 J9 f/ o0 o: z# Z4 j1 c$ @
- U- M( w/ V; q& H. n# \/ tDevicenet is only a plant base network(底层网络). It deal with BYTE level information.
B0 @6 x7 ?2 [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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