SMAR DFI302, Руководство пользователя

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DFI302 – Adding Power Supplies
7.9
DF49 / DF53 – Power Supply Impedance for Fieldbus
Description
These modules were specially designed to provide ideal impedance for Fieldbus networks. The only
difference between them is the quantity of Fieldbus ports supported:
DF49 (2 ports)
DF53 (4 ports)
The purpose of an impedance is to implement an output circuit where impedance is greater than 3
K
Ω
and in parallel with two terminators of 100
Ω
± 2% each, resulting a line impedance of
approximately 50
Ω
. This impedance can be implemented in a passive mode (50
Ω
resistance in
series with a 100 mH inductance) or in an active mode, through an impedance control circuit.
The Fieldbus Power Supply Impedance is an active non-isolated impedance control device, in
according to the IEC 1158-2 Standard. This device presents an output impedance, which in parallel
with the two bus terminators (a 100
Ω
resistor in series with a 1
µ
F capacitor) required by the
standard, resulting in a purely resistive line impedance for a broad frequency range.
The
DF49/DF53
cannot be used directly in areas with intrinsic safety specifications.
The figure below shows the Device Block Diagram. The
DF49/DF53
can be used in redundancy,
connecting their output (+ and -) in parallel. When this configuration is used, an external bus
terminator (BT302) is needed to allow the change of
DF49/DF53
in case of failure, without
interrupting the Fieldbus.
DF49/DF53
DF49/DF53
The
DF49/DF53
have LEDs to indicate power supply and overcurrent. The input terminal block has
two terminals (1A e 2A) that are connected to the external 24 Vdc. The power supply indication LED
is green and it is energized while there is external 24 Vdc power supply.
The overcurrent indication LED is red and it must be energized only in case of overcurrent, caused
by a short-circuit in the plant or by an excessive number of connected devices. The following figure
shows a DF49 / DF53 layout.
DF49
:
Four terminals
(3 to 6 A) implementing
2
independent Fieldbus ports,
2
Dip Switches for Bus
Termination activation,
1
green LED for power status and
2
red LEDs indicating overcurrent.