Rosemount 248, Справочное руководство

Страница: 18 / 80

Reference Manual
00809-0100-4825, Rev BB
August 2005
Rosemount 248
2-8
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
SET THE SWITCHES
Failure Mode
As part of normal operation, each transmitter continuously monitors its own
performance. This automatic diagnostics routine is a timed series of checks
repeated continuously. If diagnostics detect an input sensor failure or a failure
in the transmitter electronics, the transmitter drives its output to low or high
alarm depending on the failure mode configuration. (Saturation levels are
3.90 mA for standard configuration (3.8 mA if configured for NAMUR-
compliant operation) on the low end and 20.5 mA for standard or NAMUR-
compliant configuration on the high end, if the sensor temperature is outside
of range limits.) These values are also custom configurable by the factory or
using the 375 Field Communicator or AMS. See “Alarm and Saturation” on
page 3-11 for instructions on how to change the alarm and saturation levels
with the 375 Field Communicator.
NOTE
Microprocessor failures cause high alarm regardless of alarm direction (high
or low) choice.
The values to which the transmitter drives its output in failure mode depend
on whether it is configured to standard, NAMUR-compliant, or custom
operation. See “Software Detected Failure Mode” on page A-2 for standard
and NAMUR-compliant operation parameters.
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. Verify that the operating
atmosphere of the transmitter is consistent with the appropriate hazardous
locations certifications. Use extreme caution when making contact with the
leads and terminals.
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
3044-0131A
Between 250
Ω
and 1100
Ω
if no load resistor.