Emerson Rosemount 644h, Reference Manual

Page: 19 / 78

Reference Manual
00809-0100-4728, Rev HA
December 2002
2-9
Models 644H and 644R
Multichannel
Installations
Several transmitters can be connected to a single master power supply, as
shown in Figure 2-5. In this case, the system may be grounded only at the
negative power supply terminal. In multichannel installations where several
transmitters depend on one power supply and the loss of all transmitters
would cause operational problems, consider an uninterrupted power supply or
a back-up battery. The diodes shown in Figure 2-5 prevent unwanted
charging or discharging of the back-up battery.
Figure 2-5. Multichannel
Installations
WIRING
All power to the transmitter is supplied over the signal wiring. Use ordinary
copper wire of sufficient size to ensure that the voltage across the transmitter
power terminals does not drop below 12.0 V dc.
If the sensor is installed in a high-voltage environment and a fault condition or
installation error occurs, the sensor leads and transmitter terminals could
carry lethal voltages. Use extreme caution when making contact with the
leads and terminals.
NOTE
Do not apply high voltage (e.g., ac line voltage) to the transmitter terminals.
Abnormally high voltage can damage the unit. (Sensor and transmitter power
terminals are rated to 42.4 V dc.)
For multichannel installations, see above. The transmitters will accept inputs
from a variety of RTD and thermocouple types. Refer to Figure 2-6 on
page 2-10 when making sensor connections.
Use the following steps to wire the power and sensor to the transmitter:
1. Remove the terminal block cover (if applicable).
1. Connect the positive power lead to the “ + ” terminal. Connect the
negative power lead to the “ – ” terminal (see Figure 2-7).
2. Tighten the terminal screws. When tightening the sensor and power
wires, the max torque is 6-in.-lbs (0.7 N-m).
3. Reattach and tighten the cover (if applicable).
4. Apply power (see “Power Supply”).
Transmitter
No. 1
Transmitter
No. 2
R
Lead
R
Lead
R
Lead
Readout or
Controller No. 1
Readout or
Controller No. 2
To Additional
Transmitters
dc
Power
Supply
Backup
Battery
3044
-013
1A
Between 250
Ω
and 1100
Ω
if no load resistor.