Yokogawa ADMAG AXF Instrukcja Użytkownika Strona 52

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IM 1E10C1-E
7-2
7. OPERATION VIA HART COMMUNICATOR
7.1.2 Communication Line Requirements
Specifications for Communication Line:
Load resistance: 230 to 600 (including cable resistance)
When multidrop mode, see Figure 7.1.2.
Minimum cable size: 24 AWG, (0.51 mm diameter)
Cable type: Single pair shielded or multiple pair with overall shield
Maximum twisted-pair length: 6,500 ft (2,000 m)
Maximum multiple twisted-pair length: 3,200 ft (1,000 m)
Use the following formula to determine cable length for a specific application;
L =
65×10
6
(R×C)
(C
f
+10,000)
C
where: L = length in feet or meters
R = resistance in ohms, current sense resistance
C = cable capacitance in pF/ft or pF/m
C
f
= 50,000 pF
800
230
571
500
444
400
363
333
307
285
266
12 345678910 11 12 13 14 15
600
400
200
0
Load
Resistance
()
Q’ty of connected field devices
* Maximum Load Voltage: 600Ω × 25 mA = 15 V
Figure 7.1.2Load Resistance and Quantity of Devices in Multidrop Mode
The above graph shows the load resistance in case that each current output of all
connected transmitters is 4 mA.
NOTE
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