Instrument grounding system mainly include: protection grounding, work (
The Ann system grounding, COM)
And anti-static grounding and lightning protection grounding, etc.
1 protection grounding instrument and control system, protection grounding belongs to the low voltage power distribution system, so should be according to the relevant standards and methods of the electrical * *, and * * of low-voltage distribution system should be connected to the electrical grounding network.
In general, protective earthing resistance shall be no greater than 4 ohms.
2 work grounding (
The Ann system grounding, COM bus-bar)
Different forms of the instrument, its working earthing connections are not the same.
For example: three type instrument is a typical public grounding electric instrument.
Intrinsically safe system grounding is usually discussed zener type safety barrier.
Isolation type safety barrier with three isolation method, there is no need to system grounding line.
From the electrical wiring, zener safety barrier of intrinsically safe system grounding and instrument signal circuit grounding is inseparable, electrical grounding system.
has the special grounding ring, grounding ring through the grounding electrode direct contact with the media, and then through the grounding ring and the instrument flange, in order to achieve and equipotential, to eliminate interference.
3 static electrostatic discharge is characteristic of high voltage, low current, time is short.
To restrain or eliminate electrostatic discharge should adopt various measures, in addition to avoid generating electrostatic, timely discharge static electricity is one of the effective means.
Many corresponding specification, material static policy should be Shared with other grounding system grounding device.
Grounding when set 4 to have separate lightning protection system, the grounding resistance should not be greater than 1 & Omega;
The national standard GB50057 'building lightningproof design code' regulation: & other;
From the lightning protection point of view, is better is a common grounding device, it suits for all ground (
For example, lightning protection, low voltage power system, telecommunication system)
In 'petroleum chemical instrumentation grounding design code' also mentioned: according to the working principle of grounding and the relevant national standard and domestic standards, provisions of the instrument and control system, grounding, protective grounding, grounding device should be sharing a set.
Essential safety instrument system grounding should not be a separate grounding system, should be one with electrical grounding system.
Nonetheless, referred to in the grounding system of construction specifications: although grounding and protection work is linked together, but these two kinds of ground should be connected, forbid to hybrid junction (
See figure 2)
In this paper, published by the embellish of instrument science and technology co. , LTD. )
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