13
IN
IN
IN
OUT
OUT
OUT
OUT
OUT
OUT
EXT
T/S
EXT
T/S
EXT
T/S
IN
IN
IN
1
1
1
2
2
2
3
3
3
4
4
4
5
5
5
6
6
6
ime Maste
ime Slave #1
ime Slave #2
ime Slave #3
RS485 Twisted
Pair Cable
IN OUT OUT EXT
T/S
IN
1
#1
TB6
#1
TB6
#1
TB6
#1
TB6
23456
DAU Interconnection for 1pps Synchronisation
Clock Synchronisation
Each IDM DAU has an internal free running clock for time
stamping recorded data. This clock can be synchronized to an
external source via a 1 pulse per second (1pps) applied on one
of three inputs:
# The BNC co-axial connector (TTL level)
# The ST fibre connector
# Pins 1 and 3 of #1TB6 (RS485 multidrop)
Master DAUs can be equipped with an internal GPS or IRIG-B
time decoder. The ANTENNA BNC socket is provided for the
connection of the GPS, or the 1PPS BNC for IRIG-B 003, DC
level, no carrier, BCD/SB data format signal.
Note:
The DAU can be equipped with either a GPS decoder
or an IRIG B decoder.
Where multiple DAUs are installed at one site, one DAU (the
Time Master) can be used to synchronize other DAUs (time
slaves) using a 1pps (one pulse per second) signal. In this way
all DAUs are synchronized to the same time, +/- 10
:s, even if
there is no accurate external time source.
The following figure shows how DAUs are interconnected for
1pps synchronisation via RS485.
Note:
For DAUs with clock synchronisation using RS485
multidrop, the last Slave in the chain has jumper J1a
on the Analog board inserted for correct RS485
termination.
The pin out for
#1TB6 is given in the following table. The
connections are via a screw terminal adapter block that plugs
into
#1TB6.
Pin 1 A (loop in)
Pin 2 A (loop out)
Pin 3 B (loop in)
Pin 4 B (loop out)
Pin 5 External Time Stamp
Pin 6 External Time Stamp
Using an External PPS
An external pulse, 0Vdc and rising to 8Vdc, may be connected
to the 1PPS BNC connector on the rear of the DAU. (BNC
centre = 8Vdc pulse, BNC outer = 0Vdc).
The pulse must be greater than a minimum of 10
:s wide. The
pulse must not exceed 20Vdc.
The second is marked as the rising edge of this pulse.
Note:
If an external pps is to be used then jumper J2 on
the Analog board must be set to the A position.
For DAUs using IRIG-B via the 1PPS BNC connector
ensure jumper J2 on the Analog board is set to
position B.
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