Model: MC-1-DE
Doc Ref. No:-m05dom102
Issue No:-00
Page 53 of 76
User’s Manual
4) Input impedance of end device: -By connecting, multiple devices to GPS TIME SYNC UNIT
MC-1-DE results in decrease of drive voltage due to increase in load current. In many cases, model
MC-1-DE time code output are “fanned out” to a no of devices. The exact no of possible load can be
determine from input impedance of each connected devices. To know input impedance of connected
devices please refer specific device manual.
9.2.2.7.1 Connecting IRIG-B DCLS (TTL):
To drive multiple load from IRIG-B DCLS output connect all end devices in parallel. To determine load
current for one IRIG-B DCLS output
•
Determine no of load devices to be connected
•
Determine input impedance of each load devices (Rdev)
•
Calculate load current of each device (Idev = 5V ÷ Rdev)
•
Sum all the load device current and compare with model MC-1-DE load capacity current
9.2.2.7.2 Connecting IRIG-B AM:
The main difference in computing the load capacity for IRIG-B AM and IRIG-B DCLS is that some of
the modulated IRIG-B decoders are sensitive to the peak-to-peak voltage. Connecting multiple devic-
es with MC-1 IRIG-B AM output causes increase in current flow which affects the Pick-Pick output
voltage to decrease. GPS TIME SYNC UNIT MC-1-DE IRIG-B AM Time code signal output imped-
ance is 100
Ω
.
9.3 Timing Output – NTP
9.3.1 NTP Introduction:
NTP (Network time protocol) is a common method for synchronization of hardware clocks in local and
global Ethernet networks. The software package NTP is an implementation of the actual version 3
[Mills90], based on the specification RFC-1305 from 1990 (directory doc/NOTES). NTP protocol is
used to synchronize and maintain the time among distributed networks of servers and clients. NTP
protocol is evolved from Time protocol but is designed to maintain accuracy and robustness even on
the networks involving multiple gateways, high network path delays and unreliable nets. NTP protocol
is applied on the application layer on UDP based IP layer.
The purpose of NTP is to convey timekeeping information (in terms of UTC) from NTP servers to oth-
er time clients via the Internet and also to cross-check clocks and mitigate errors due to equipment or
propagation failures. In NTP basic model, NTP client device sends the NTP packet message over
wire to NTP server (time source) at prefixed/defined interval (as per NTP standard). The NTP server
interchanges IP addresses and ports, overwrites certain fields in the message, inserts current time-
stamp in packet, recalculates the checksum and returns the message immediately to NTP client. In-
formation included in the NTP message allows the client to determine the server time with respect to
local time and adjust the local clock accordingly. After NTP message is received, NTP client calcu-
lates time offset, own local clock frequencies and update in its database at regular intervals to main-
tain the clock time synchronization with NTP server time. This may result in either a step-change or a
gradual phase adjustment in time of the NTP client’s local clock to reduce the offset to zero or as min-
imum as possible. The accuracies achievable by NTP client depend strongly on the precision of the
local-clock frequency and stringent control of device and process latencies.
NTP architecture model consists of number of primary reference sources, synchronized by wire or ra-
dio clock. There are other several multiple secondary time sources/clients which are arranged in hie-
rarchal manner in network which request time from primary reference sources. Under normal cir-
cumstances it is intended that the synchronization subnet of primary and secondary servers assumes
