3.2 Network topology
HART bus can operate in one of these two network configurations—point to point and multi-drop.
1. Point to Point Mode :
In point to point mode, the analog signal is used to communicate one process variable and the
digital signal gives access to secondary variables and other data that can be used for operations,
commissioning, maintenance and diagnostic purposes. Only one HART slave device can exist in
HART bus and the polling address must be zero.
Figure 16: “Point to Point” topology
2. Multi-drop Mode :
In multi-drop mode, all process values are transmitted digitally. The polling address of all field
devices must be bigger than 0 and between 1 ~ 15. The current through each device is fixed to a
minimum value (typically 4 mA). The maximum HART device number in HART bus is up to 15.
[ Note ]
1. The built-in resistor in HRT-710 is 250 Ohm with 1/4W. Therefore, HRT-710 supports to
connect the maximum 7 HART devices simultaneously. If the HART devices in multi-drop
mode are more than 7, then users need to disconnect the built-in resistor in HRT-710
(prevent to burn down) and use the external 250 Ohm resistor with 1W.
2. The built-in resistor in HRT-310 is 250 Ohm with 1W and it allows up to 15 HART devices
to be connected.
HRT-710 / HRT-310 User Manual
Version 1.31
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