HART Communication
5
TI 12A01A02-60E
l
Unique Features of HART Communication
(1) Multi-drop mode
Up to 15 field devices put in multi-drop mode can be connected in parallel on a single
twisted-pair cable. To enable the multi-drop mode, set the device address to a unique
number from 1 to 15.
Enabling the multi-drop mode fixes the outputs of the corresponding field devices to 4 mA
DC and thus disables the 4–20 mA analog output signals as well as burn-out outputs.
NOTE
When the FLXA202/FLXA21 is used in the multi-drop mode, the output signal is changed
from 12.5 mA DC to 4 mA DC just after the power is turned on. Enough power supply for the
instruments is to be provided.
NOTE
Multi-drop mode communication requires the devices on the link to be given unique device
addresses for polling (polling addresses). If the same address is set in two or more devices,
correct communication is disabled.
Communication actions in multi-drop mode:
a. To use multi-drop mode communication, an address needs to be set for each device for
polling. To enable searching for the devices working in the multi-drop mode, setup tools
usually require search address settings, too.
b. When the HART setup tool starts or carries out a device search, it searches through device
addresses that should be set uniquely. The tool then shows a list of devices thus searched
by polling address, allowing for communication with selected devices.
c. To add a device and enable communication with it, restart the setup tool or carry out a
device search to make the tool recognize the added device.
Canceling multi-drop mode:
To release a device from the multi-drop mode, set the polling address to zero.
(2) Burst mode
Burst mode allows a field device to be configured to transmit digital process values
(selected from the PV, output percent, and 4–20 mA output) continuously three times every
second. Burst mode can be initiated from a HART setup tool. In order to use burst mode,
however, the setup tool and receiver equipment such as a distributed control system must
support burst mode.
Burst made is set in the following menu.
Online
+– Sensor 1
+– Setup
+– Commissioning
+– Advanced Setup
+– Communication
Jun. 29, 2017-00
