Siemens FC700A manual 6.2.1Diagram, Zc =, Bus systems

Bus systems

6.2.1Diagram

Ri [Ohm]

200
190
180
170
160
150
140
130
120
110					Standard
100
90
80					Lifeline
70
60					Radox
50
					MICC
40
30
20
10
0 0	20	40	60	80	100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740

Rd [Ohm]

2.Procedure

Request characteristic impedance of the cable from manufacturer (45Ω ... 200Ω) Select the value of the Ri the same as the value of the cable characteristic im-

pedance and insert the four end-of-line resistors on the p.c.b. Insert two driver resistors Rd = Ri x 3.65 on the p.c.b. Each C-Bus user must be adapted

If only the inductance and the capacitance are known for a cable, the impedance can be calculated with the aid of the following formula:

Zc =	Lc
	Cc

Zc:	Cable impedance [Ω]
Lc:	Cable inductance [∝H]
Cc:	Cable capacitance [∝F]

3.Mixing of different types of cable

In a C-Bus loop (or stub line) only one type of cable may be used.

4.Operation as a stub line

If the C-Bus is operated as a stub line, two end-of-line resistors (values as for Ri) must be inserted externally at both ends of the line (default 110Ω). In the choice of other cables the above rules apply (the Ri are in this case the external end-of-line resistors).

For further information, see document 007831

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Siemens Building Technologies	007836_a_en_--.doc
Fire & Security Products	03.2004