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
Ω
(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
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
600
400
200
0
Load
Resistance
(
Ω
)
Q’ty of connected field devices
* Maximum Load Voltage: 600
Ω ×
25 mA = 15 V
Figure 7.1.2 Load 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
