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Rosemount Model 444 Alphaline Temperature Transmitters
2-4
ELECTRICAL
CONSIDERATIONS
This section contains information that you should consider when preparing to
install Model 444 transmitters. Read this section carefully before going on to the
installation procedures. Metal conduit should be used to enclose cabling for best
results in electrically noisy environments.
Power Supply
The dc power supply should provide power with less than 2% ripple. The input
voltage versus load limitation relationship for 4–20 mA transmitters is shown in
Figure 2-3. Figure 2-4 shows field wiring for a standard Model 444 transmitter.
Figure 2-5 shows field wiring for Models 444LL and 444LM low-power voltage
output units, which require 100K ohms minimum load. The total R-load is the
sum of the resistance of the signal leads and the load resistance of the controller,
indicators, and related devices. Note that the resistance of intrinsic safety
barriers, if used, must be included in the total load.
FIGURE 2-3. Model 444
Load Limits.
Field Wiring
All power to the transmitter is supplied over the signal wiring. Signal wiring
need not be shielded, but use twisted pairs for best results. Do not run
unshielded signal wiring in conduit or open trays with power wiring, or near
heavy electrical equipment. To power the transmitter, connect the positive power
lead to the terminal marked “+” and the negative power lead to the terminal
marked “–” (see Figures 2-4 and 2-5). Tighten the terminal screws to ensure
adequate contact. No additional power wiring is required.
Load (Ohms)
Operating
Region
1650
1500
1000
500
0
Power Supply Load Limitations
R
LOAD (MAX.)
=50ϫ (V
(MIN.)
– 12)
12 20 30 40
Power Supply (V dc)
Voltage
Too Low
Explosions may result in death or serious injury.
Do not remove the instrument cover in explosive
atmospheres when the circuit is alive.
High voltage that may be present on leads can cause
electrical shock. Avoid contact with leads and terminals.
Do not apply high voltage (e.g. ac line voltage) to the
transmitter terminals. Abnormally high voltage can damage
the unit.