FloBoss 407 Instruction Manual
3-28 Rev 5/00
3.4.16 HART Interface Module
The HART Interface module allows the ROC/FloBoss to interface with up to 10 HART devices per I/O
slot. The HART module provides “loop source” power (+T) on terminal A and two channels for
communications on terminals B and C. The +T power is regulated by a current limit. If the power
required by all connected HART devices exceeds 40 milliamps (more than an average of 4 milliamps
each), the total number of HART devices must be reduced.
The HART module polls one channel at a time. If more than one device is connected to a channel in
a multi-drop configuration, the module polls all devices on that channel before it polls the second
channel. The HART protocol allows one second per poll for each device, so with 5 devices per channel
the entire poll time for the module would be ten seconds.
In a point-to-point configuration, only one HART device is wired to each HART module channel.
In a multi-drop configuration, two to five HART devices are connected to a channel. In either case,
terminal A (+T) is wired in parallel to the positive (+) terminal on all of the HART devices, regardless
of the channel to which they are connected. Channel 1 (terminal B) is wired to the negative (-) terminal
of a single HART device, or in parallel to the negative terminals of two to five devices. Likewise,
channel 2 (terminal C) is wired to the negative (-) terminal of a single HART device, or in parallel to
the negative terminals of a second group of two to five devices. Refer to Figure 3-26.
HART MODULE
C
DOC0295A
B
A
+
-
HART DEVICE 1
ROC-POWERED
+T
I LIMIT
-
+
-
+
MUX
MODEM
ROC-POWERED
HART DEVICE 2
ROC-POWERED
HART DEVICE 5
HART DEVICE
ROC-POWERED
-
+
CHANNEL 1, MULTI-DROP MODE CHANNEL 2, POINT-TO-POINT MODE
Figure 3-26. Field Wiring for a HART Interface Module
To Next Page
Loading...
