Reference Manual
00809-0100-4793, Rev CA
August 2004
Rosemount 8742C
2-6
Supply Wire Requirements
Use 12 to 18 AWG wire rated for the proper temperature application. For
connections in ambient temperatures above 140 °F (60 °C), use a wire
rated for 176 °F (80 °C). For ambients greater than 176 °F (80 °C), use a
wire rated for 230 °F (110 °C).
Disconnects
Connect the device through an external disconnect or circuit breaker.
Clearly label the disconnect or circuit breaker and locate it near
the transmitter and per local electrical control.
Installation Category
The installation category for the Rosemount 8742C is
(Overvoltage) Category II.
Overcurrent Protection
The Rosemount 8742C Flowmeter Transmitter requires overcurrent
protection of the supply lines. Maximum ratings of overcurrent devices are as
follows:
Transmitter
Communication Input
The F
OUNDATION
fieldbus communication requires a minimum of
9 V dc and a maximum of 32 V dc at the transmitter communication terminals.
NOTES
•
Do not
exceed 32 V dc at the transmitter communication terminals.
•
Do not
apply ac line voltage to the transmitter
communication terminals.
Improper supply voltage can damage the transmitter.
Power Conditioning
Each fieldbus power supply
requires
a power conditioner to decouple the
power supply output from the fieldbus wiring segment.
Field Wiring
Power independent of the coil power supply must be supplied for F
OUNDATION
fieldbus communications. Use shielded, twisted pair for best results. For new
installations or to get maximum performance, twisted pair cable designed
especially for fieldbus should be used. Table 2-1 details cable characteristics
and ideal specifications.
Table 2-1.
Ideal Cable Specifications
for Fieldbus Wiring
Power System
Fuse Rating
Manufacturer
110 V ac
250 V; 1 Amp, Quick Acting
Bussman AGCI or Equivalent
220 V ac
250 V; 0.5 Amp, Quick Acting
Bussman AGCI or Equivalent
See “Safety Messages” on page 2-1 for complete warning information.
Characteristic
Ideal Specification
Impedance
100 Ohms ± 20% at 31.25 kHz
Wire Size
18 AWG (0,8 mm
2
)
Shield Coverage
90%
Attenuation
3 db/km
Capacitive Unbalance
2 nF/km
Содержание 8700 Series
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