Emerson Rosemount 644 Reference Manual page 75

Reference Manual
00809-0200-4728, Rev RA
4.3.4 Wiring with a Rosemount 333 HART Tri-Loop
mA only)
Use the dual-sensor option 644 transmitter that is operating with two sensors in conjunction
with a 333 HART Tri-Loop HART-to-Analog Signal Converter to acquire an independent 4–20 mA
analog output signal for each sensor input. The 644 transmitter can be configured to output
four of the six following digital process variables:
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

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
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 333 HART Tri-Loop HART-to-Analog Signal Converter Reference
Manual (document number 00809-0100-4754) for complete installation information.
Power supply
An external power supply is required to operate the 644 and is not included. The input voltage
range of the transmitter is 12 to 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 2% 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.
Electrical Installation
Sensor 1
Sensor 2
Differential temperature
Average temperature
First good temperature
Transmitter terminal temperature
Section 4: Electrical Installation
™
(HART/4–20
Figure 2-6 on page 19 for basic installation
April 2015
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