Emerson 8800A, Руководство по эксплуатации продукта

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2-27
Installation
Wiring Procedure
The signal terminals are located in a compartment of the electronics
housing separate from the flowmeter electronics. Connections for a
HART-based communicator and a current test connection are above the
signal terminals. Figure 2-19 illustrates the power supply load
limitations for the flowmeter.
Power Supply
The dc power supply should provide power with less than two percent
ripple. The total resistance load is the sum of the resistance of the
signal wiring and the load resistance of the controller, indicator, and
related pieces. Note that the resistance of intrinsic safety barriers, if
used, must be included.
NOTE
A minimum loop resistance of 250 ohms is required to exchange
information with a HART-based communicator. With 250 ohms
of loop resistance, the flowmeter will require a minimum power supply
voltage (V
ps
) of 16.8 volts to output 24 mA.
If a single power supply is used to power more than one Model
8800C flowmeter, the power supply used and circuitry common
to the flowmeters should not have more than 20 ohms of
impedance at 1200 Hz.
Figure 2-19. Power Supply Load Limitations
Table 2-18. Wire Resistance per 1,000 Feet (305 m)
Gage Number
A.W.G.
Ohms per 1,000 ft (305 m)
at 68 °F (20 °C) Equivalent
14 2.525
16 4.016
18 6.385
20 10.15
22 16.14
24 25.67
1500
1000
500
0
42 10.8
R
max
= 41.7(V
ps
– 10.8)
V
ps
= power supply voltage (volts)
R
max
= maximum loop resistance (ohms)
Power Supply (volts)
Lo
a
d
(
O
hm
s
)