Distribution and short circuit protection of the h

2022-07-31
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Distribution and short circuit protection of FF Fieldbus and its explosion-proof

Foundation Fieldbus Generally referred to as FF fieldbus, it is divided into H1 and H2 buses. H1 adopts fieldbus physical layer conforming to IEC standard; H2 uses high-speed Ethernet as the physical layer. This paper only discusses the power distribution, short circuit protection and explosion-proof technology of FF H1 fieldbus

The main electrical characteristics of the physical layer of the

h1 fieldbus are as follows:

data transmission mode: digital, bit synchronization; Transmission baud rate: 31.25kbit/s; Driving voltage: 9 ~ 32vdc; Signal current: ± 9ma; Cable type: shielded twisted pair; Wiring topology: linear, tree, star and composite; Cable length: less than or equal to 1900m (without repeater); Length of branch cable: 30 ~ 120m; Number of hitching equipment: less than or equal to 32 (without repeater); Number of available repeaters; Less than or equal to 4 sets; Applicable explosion-proof methods: intrinsically safe explosion-proof methods, etc

Distribution of

2ff Fieldbus

h1 fieldbus completes power supply and two-way digital communication for multiple field instruments on a shielded twisted pair cable. The H1 card equipped in the control system, which makes the battery system unable to work for a long time, is usually only responsible for two-way communication with field instruments. The bus power distribution shall be undertaken by the special FF power distribution, as shown in Figure 1

h1 bus consists of bus network in the unit of "segment". Each H1 card usually has two or four ports. Each bus section shall be equipped with one FF distributor. Both ends of each bus section shall be equipped with one end (also known as terminal resistance) to eliminate the echo of high-frequency signal. Since the bus adapter circuit in the FF distributor usually contains one terminal, the user also needs to equip one terminal at the end of each bus

after equipped with H1 card, FF distributor and terminal, FF field bus instrument can be connected to this section of bus. According to the relevant interoperability provisions of FF protocol, any field instrument registered by bus foundation shall be able to be connected to H1 bus

how many field instruments can be connected to each H1 bus, and how long can the bus cable be set? Generally, the supplier of H1 card will specify the limit quantity (e.g. 16 sets) and recommended quantity (e.g. 8 sets) of instruments attached to each section. However, the distribution capacity of FF distributor will also affect the number of meters that can be hooked up and the length of bus cable. For example, the distribution current of FF distributor limits the total power consumption current of field instruments. The greater the distribution current, the more instruments can be connected. When the number of connected instruments is constant, the higher the distribution voltage is, the longer the bus cable can be set. This is an example to illustrate the estimation of the number of connected field instruments and cable length in the application of field bus distributor

distribution capacity of the set distributor: 24vdc/400ma

ff bus period, Wharton's products are widely used in industrial water purification, household water purifier, seawater desalination and other fields with strong demand. Transmitter power consumption: 9v/17.5ma

ff bus valve positioner power consumption: 9v/26ma

ff fieldbus type a cable distribution resistance: 44 Ω/km

1) number of field instruments attached

transmitters: 400 ÷ 17.5=22.8 (sets)

positioners: 400 ÷ 26=15.3 (sets)

therefore, 22 transmitters or 15 valve positioners can be attached to each bus. In practice, each H1 bus section is usually connected with 16 field instruments, including 4 to 8 valve positioners

2) cable length: it is assumed that 8 transmitters and 8 valve positioners are connected to the bus

then the total power consumption of field instruments is

(8 × 17.5)+(8 × 26) =348 (MA)

the allowable voltage drop of the bus cable is

24 - 9 = 15 (V)

the allowable total cable resistance is

15v ÷ 348mav=43.1 Ω

the cable length is

43.1 ÷ 44=0.980 (km)

therefore, when 8 transmitters and 8 valve positioners are attached to the bus, the cable length can reach 980m

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