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本帖最后由 td456 于 2010-3-25 08:06 编辑
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$ c# z: A; \ z2 m: N5 T0 i 1# 移民电工
7 Y' O+ ~0 S; k; s" gHart protocol is something between analog and digital,it is a digitally enhanced 4-20mA smart instrument communication.2 o o1 L, G8 d& z% W8 X
& J r7 ~. s( `2 h"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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! n2 C: r: W& B6 P: \, J6 `% Y: hIn DCS, HART is still treated as AI(Analog In) signal.; z2 w& ?! U% a
Anyway it is only a transitional protocol and it is being replaced by Fieldbus or Profibus.
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' J9 N# L3 E9 h, kDevicenet is only a plant base network(底层网络). It deal with BYTE level information.% h7 p3 q% B3 V H3 n; X
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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