MULTIDROP WITH HART FIELD CONTROLLERS
HART field controllers can also be wired in a multidrop network (Figure 9). Each analog output signal from the transmitter/controllers is isolated
from every other output signal, which
provides a cost-effective
HART network configuration.
In this case, the analog signals are not fixed and are used for the output signal to the controlled device.
Figure 9: HART
Controllers with Multidrop
Connecting HART field devices in a multidrop network can provide significant installation savings. The total cable length in a multidrop network is typically less than the maximum cable length in point-to-point connections because the capacitance of the additional devices reduces the distance that the HART signal can be carried (see Wiring and
Installation on page 17).
Using the polling address
structure of the HART protocol, up to 15 devices can be connected in a multidrop network. The analog current of a HART device can be fixed by setting its polling address to a number other than zero.
With the HART protocol, each field instrument should be configured with different polling addresses or tag numbers before being connected to a multidrop network—otherwise, the master will not be able to establish communication with the slave devices.
