Rockwell Automation 1797-OE8H FLEX Ex HART Analog Modules User Manual - Manual (Page 21)

Publication 1797-6.5.3 - March 2006
About the FLEX Ex HART Analog Modules 1-7
How to Use the
HART Capabilities Before using the HART capabilities, be sure that:
• the I/O module and the associated field device are working properly in
the analog 4 to 20 mA mode.
• the I/O module is configured for 4 to 20 mA range.
• the field device is HART capable.
• no more than one HART field device is connected to each channel.
• input filtering is set to a valid (defined) value.
HART Implementation
Overview The FLEX Ex HART modules act as intelligent HART multiplexers. Basically,
the module learns which HART devices are attached to its channels and then
routes HART messages, as appropriate, between the HART field devices and
the Flexbus. Since the HART modules act as intelligent HART multiplexers,
HART commands can be issued to the HART modules themselves.
Communication on the Flexbus occurs between the adapter and the HART
module. The adapter converts these messages to the appropriate network
format for communication with the controlling controller. The controlling
controller gets its command from the user program, storing the responses in
its memory.
In its basic form, your ladder-logic program issues an MSG instruction
containing a HART command. The MSG instruction is routed to the
appropriate adapter and FLEX Ex I/O module. Upon receiving the message,
the HART module routes the message to the appropriate channel and gathers
the HART field device response. To retrieve this response, your ladder-logic
program issues another MSG instruction.
Controller
User Program
Adapter FLEX Ex HART
I/O Module HART
Field Device
Command
Response
For Example,
ControlNet
Flexbus 4 to 20 mA