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Electrical Installation
July 2016
4.3.4
Wiring with a Rosemount 333 HART Tri-Loop
only)
Use the dual-sensor option Rosemount 644 Transmitter that is operating with two sensors in
conjunction with a Rosemount 333 HART Tri-Loop HART-to-Analog Signal Converter to acquire an
independent 4–20 mA analog output signal for each sensor input. The Rosemount 644 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
Refer to the Rosemount 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 Rosemount 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.
Figure 4-3. Load Limits
Maximum Load = 40.8 X (Supply Voltage - 12.0)
1240
1100
1000
750
500
250
0
60
4–20 mA dc
Operating
Region
10
20
30
40 42.4
12.0
Supply Voltage (Vdc)
Figure 2-6 on page 17
for basic installation information.
Reference Manual
00809-0100-4728, Rev MB
™
(HART / 4–20 mA
Electrical Installation
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