Emerson Rosemount 644 Reference Manual page 77

Reference Manual
00809-0200-4728
Load limitation
The power required across the transmitter power terminals is 12 to 42.4 Vdc (the power
terminals are rated to 42.4 Vdc). To prevent damaging the transmitter, do not allow
terminal voltage to drop below 12.0 Vdc when changing the configuration parameters.
4.3.3 Ground the transmitter
Sensor shielding
The currents in the leads induced by electromagnetic interference can be reduced by
shielding. Shielding carries the current to ground and away from the leads and electronics.
If the ends of the shields are adequately grounded, only a small amount of current will
actually enter the transmitter. If the ends of the shield are left ungrounded, voltage is
created between the shield and the transmitter housing and also between the shield and
earth at the element end. The transmitter may not be able to compensate for this voltage,
causing it to lose communication and/or go into alarm. Instead of the shield carrying the
currents away from the transmitter, the currents will now flow through the sensor leads
into the transmitter circuitry where it will interfere with the circuit operation.
Emerson.com/Rosemount
Figure 4-4: Powering the Transmitter for Bench Configuration
Head mount and Field mount
C
A
A. Field communicator
B. Power supply
C. 248 Ω ≤ RL ≤ 1100 Ω
D. Recorder (optional)
E. Ammeter (optional)
Note
• Signal loop may be grounded at any point or left ungrounded.
• A Field Communicator may be connected at any termination point in the signal
loop. The signal loop must have between 250 and 1100 ohms load for
communications.
• Max torque is 6 in-lb (0/7 N-m).
D
E
B
Electrical Installation
March 2021
Rail mount
D
C
_
+
_
+
E
+
_
_
+
B
A
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