Reference Manual
00809-0100-4664, Rev BA
January 2010
4-29
Rosemount 8712
Alarm Level
The alarm level allows you to drive the transmitter to preset values if an alarm
occurs. There are two options:
• Rosemount Alarm and Saturation Values
• NAMUR-Complaint Alarm and Saturation Levels
HART Output
Multidrop configuration refers to the connection of several flowmeters to a
single communications transmission line. Communication occurs digitally
between a HART-based communicator or control system and the flowmeters.
Multidrop mode automatically deactivates the analog output of the
flowmeters. Using the Field Communications protocol, up to 15 transmitters
can be connected on a single twisted pair of wires or over leased phone lines.
The use of a multidrop installation requires consideration of the update rate
necessary from each transmitter, the combination of transmitter models, and
the length of the transmission line. Multidrop installations are not
recommended where intrinsic safety is a requirement. Communication with
the transmitters can be accomplished with commercially available Bell 202
modems and a host implementing the HART protocol. Each transmitter is
identified by a unique address (1-15) and responds to the commands defined
in the HART protocol.
Variable Mapping
Variable mapping allows you to configure the variables that are mapped to the
tertiary and quaternary variables. The primary and secondary variables are
fixed and cannot be configured.
• PV is configured for flow
• SV is configured for pulse
Tertiary Variable
The tertiary variable maps the third variable of the transmitter. This variable is
a HART only variable and can be read off of the HART signal with a HART
enabled input card, or can be burst for use with a HART Tri-Loop to convert
the HART signal to an analog output. Options available for mapping to this
variable are:
•Forward Gross
• Forward Net
• Reverse Gross
• Electronics Temp
Field Comm. 1, 4, 2, 6
Table 4-3. Rosemount (Standard) Alarm and Saturation Values
Level 4-20 mA Saturation 4-20 mA Alarm
Low 3.9 mA 3.75 mA
High 20.8 mA 22.6 mA
Table 4-4. NAMUR-Compliant Alarm and Saturation Values
Level 4-20 mA Saturation 4-20 mA Alarm
Low 3.8 mA 3.5 mA
High 20.5 mA 22.6 mA
Field Comm. 1, 4, 2, 7
Field Comm. 1, 4, 2, 7, 1
Field Comm. 1, 4, 2, 7, 1, 1
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