8. OPERATION VIA HART COMMUNICATOR
8.1 Conditions of Communication Line
8.1.1Interconnectwion between AXFA11 and HART Communicator
I + | I - |
AXFA11
The HART Communicator can interface with the AXFA11 from the control room, the AXFA11 site, or any other wiring termination point in the loop, provided there is a minimum load resistance of 230 between the connection and the receiving instrument. To communi- cate, it must be connected in parallel with the AXFA11, and the connections must be non- polarized. Figure 8.1.1 illustrates the wiring connections for a direct interface at the AXFA11 site. The HART Communicator can be used for remote access from any terminal strip as well.
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| Control room | |
| 4 to 20 mA DC signal line | Terminal board | ||
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| Relaying |
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| terminals |
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| Receiving instrument | |
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| load resistance: | |
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| 230 Ω to 600 Ω | |
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| HART | HART | |
| HART | Communicator | Communicator | |
| Model 275 | Model 275 | ||
Communicator | ||||
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Model 275
F0802.EPS
Figure 8.1.1 Interconnection Diagram
8.1.2Communication Line Requirements
Specifications for Communication Line: |
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Load resistance: | 230 to 600 (including cable resistance) | |
Minimum cable size: 24 AWG, (0.51 mm diameter) | ||
Cable type: | Single pair shielded or multiple pair with overall shield | |
Maximum | 6,500 ft (2,000 m) | |
Maximum multiple
Use the following formula to determine cable length for a specific application:
L = | 65⋅ 106 | – | (Cf+10,000) |
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(R⋅ C) |
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| where: | L = length in feet or meters | ||
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| R = resistance in ohms, current sense resistance | |
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| C = cable capacitance in pF/ft or pF/m | |
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| Cf = 50,000 pF | |
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