Rosemount 3491, Reference Manual, Page: 15 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
2-3
Rosemount 3490 Series
CONTROL UNIT
FUNCTIONS
For a full guide to programming the Rosemount 3490 Series Control Unit, see
“Programming” on page 4-9.
Standard functions
(Models 3491/3492/3493)
Using either the input from a 4-20mA or HART transmitter, all models of the
3490 Control Unit will provide the following standard functions:
•
Calculation and display of the 3490’s primary variable (PV).
The user can choose this to be the reading coming from the transmitter,
which may be any measurement. For example, the Rosemount 3100
Series of transmitters can measure the liquid level or distance-to-surface,
or calculate tank content or flow rate in an open channel structure
e.g. a flume or weir. A totaliser function is included.
The Control Unit is pre-programmed with standard volumetric and flow
equations to convert a level signal into contents or flow, and also has a
20-point user-programmable look-up table for non-standard applications.
• Output a 4-20mA signal.
The 4-20mA output is usually proportional to the displayed PV, and is
displayed in bargraph form (0% to 100%).
• Relay control functions.
There are five freely assignable relays. Relay 5 is a fault relay by default,
which may be assigned to control duty if required. The other relays are
available for the user to set them to operate at chosen values of the
displayed PV, or other calculated values.
The control unit is pre-programmed with a selection of popular pump
control routines for wet well and sump control, along with energy saving
overrides.
• Voltage-free (digital) contact close input.
Up to two voltage-free contact closure inputs may be connected, allowing
external override of control functions if desired.
• Programming a transmitter using the control unit
When a Rosemount 3100 or 3300 Series HART transmitter is connected,
the 3490 will recognize the transmitter, allow selection of variables to be
processed, and allow full access to and programming of the transmitter
configuration parameters, eliminating the need for any other HART
programming device.
Any other HART transmitter can be connected to the 3490 - in this case
the 3490 will recognize the transmitter as an "unknown instrument" and
will allow access to and programming of the Universal and Common
Practice HART commands.
Difference, sum and
product functions
(Model 3492)
Model 3492 has all the standard functions listed above, and extra functions
for calculating the difference, sum, or product of two separate inputs from
HART transmitters.
Logging functions
(Model 3493)
Model 3493 has all the standard functions listed above, and a 7000 event
logging facility.