Emerson Rosemount 644 Reference Manual page 82

Electrical Installation
March 2021
4.3.4 Wiring with a Rosemount 333 HART Tri-Loop (HART/4–
20 mA only)
Use the dual-sensor option transmitter that is operating with two sensors in conjunction
with a Rosemount 333 HART
independent 4–20 mA analog output signal for each sensor input. The transmitter can be
configured to output four of the six following digital process variables:
• Sensor 1
• Sensor 2
• Differential temperature
• Average temperature
• First good temperature
• Transmitter terminal temperature
The HART Tri-Loop reads the digital signal and outputs any or all of these variables into as
many as three separate 4–20 mA analog channels. Refer to
information. Refer to the Rosemount 333 HART Tri-Loop HART-to-Analog Signal Converter
Reference Manual
Power supply
An external power supply is required to operate the transmitter and is not included. The
input voltage range of the transmitter is 12–42.4 Vdc. This is the power required across
the transmitter power terminals. The power terminals are rated to 42.4 Vdc. With 250
ohms of resistance in the loop, the transmitter requires a minimum of 18.1 Vdc for
communication.
The power supplied to the transmitter is determined by the total loop resistance and
should not drop below the lift-off voltage. The lift-off voltage is the minimum supply
voltage required for any given total loop resistance. If the power drops below the lift-off
voltage while the transmitter is being configured, the transmitter may output incorrect
information.
The DC power supply should provide power with less than two percent ripple. The total
resistance load is the sum of the resistance of the signal leads and the load resistance of
any controller, indicator, or related piece of equipment in the loop. Note that the
resistance of intrinsic safety barriers, if used, must be included.
Note
Permanent damage to the transmitter could result if the voltage drops below 12.0 Vdc at
the power terminals, when changing transmitter configuration parameters.
82
®
Tri-Loop HART-to-Analog Signal Converter to acquire an
for complete installation information.
Reference Manual
00809-0200-4728
Figure 2-7 for basic installation
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