Schmid Watson Installation Guide Page 49

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LTU/NTU SZ-DOC-W5-1.pd
f
Operating Manual
V
ersion: 1.5
Revision: 2002-09-10 40
Caution:
A 48V
DC
battery supply must not be connected directly to the “AC/DC adapter” connector! High
voltage transients from the DSL line may damage other equipment connected to the battery. A
DC/DC converter with 4kV transient isolation voltage should be used in this case.
6.2.2 Power Failure Alarm
The power supply bit ps is used to indicate the status of the local power supply in the NTU. The
power status bit is set to ONE if power is normal and to ZERO if the power has failed;
On loss of power at the NTU, there is enough power left to communicate three "Power Loss"
messages towards the LTU. In case of a failure of the NTU's power supply, both LEDs will be
extinguished.
6.3 Remote Powering
Remote power feeding is supported. The remote NTU-R can be fully powered over the DSL
twisted wire-pairs from the LTU-R. The remote power-feeding concept has the following
characteristics:
Per pair remote feeding (no “phantom”-circuit)
Cross-wiring tolerant
Power feeding voltage within limits of TS 101 524 (max. 112V
DC
)
Independent current limiters on a per pair basis (microcontroller - controlled)
Tolerant against micro-interruptions
Automatic system restart after power failure
The remote power voltage of 111V
DC
is generated locally on each LTU-R and is referenced to
earth. In case of overvoltage ( |U| > 118V
DC
), the unit is immediately shutdown within 100ms and
can be reactivated only after an interruption of at least 500ms of its -48V
DC
supply / supplies. The
LTU is able to feed up to 56±3mA
DC
over each DSL pair.
The ability of providing remote power to the DSL line can be permanently switched off by setting
the R/L jumpers located on the PCB in position "RPWR OFF". In this case, the DSL line interface
is disconnected from the remote power circuitry and it behaves like the DSL interface of a NTU,
i.e. it is floating.
Caution:
If changing the remote powering condition the LTU must not be connected to the power supply.
For the LTU in minirack the external power supply must be disconnected first before opening the
cover!
Remote powering depends strongly on the power consumption of the NTU (which in turn
depends slightly on the supply voltage) as well as the loop resistance (wire diameter and cable
length).
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