MAN-RTM-0003 - Real-time Clock Operator`s Guide

MAN-RTM-0003 - Real-time Clock Operator`s Guide
CMG-RTM Real-time
Clock/GPS Emulator
Operator's Guide
Document No: MAN-RTM-0003
Issue B, March 2016
Designed and manufactured by
Güralp Systems Limited
3 Midas House, Calleva Park
Aldermaston RG7 8EA
England
CMG-RTM Real-time Clock/GPS Emulator
Contents
Table of Contents
1 Preliminary Notes.................................................................................................................... 3
1.1 Proprietary Notice...................................................................................................... 3
1.2 Warnings, Cautions and Notes...................................................................................3
1.3 Manuals and Software............................................................................................... 3
2 Introduction.............................................................................................................................. 4
3 Operation................................................................................................................................... 5
4 Connector pin-outs................................................................................................................. 9
4.1 GPS Output, Power Input (right-hand connector).....................................................9
4.2 GPS Input (left-hand connector)..............................................................................10
5 Specifications.......................................................................................................................... 11
6 Revision history..................................................................................................................... 12
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Preliminary Notes
1 Preliminary Notes
1.1 Proprietary Notice
The information in this document is proprietary to Güralp Systems Limited and may
be copied or distributed for educational and academic purposes but may not be used
commercially without permission.
Whilst every effort is made to ensure the accuracy, completeness and usefulness of
the information in the document, neither Güralp Systems Limited nor any employee
assumes responsibility or is liable for any incidental or consequential damages
resulting from the use of this document.
1.2 Warnings, Cautions and Notes
Warnings, cautions and notes are displayed and defined as follows:
Warning: A black cross indicates a chance of injury or death if the
warning is not heeded.
Caution: A yellow triangle indicates a chance of damage to or failure
of the equipment if the caution is not heeded.
Note: A blue circle indicates indicates a procedural or advisory note.
1.3 Manuals and Software
All manuals and software referred to in this document are available from the Güralp
Systems website: www.guralp.com unless otherwise stated.
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Introduction
2 Introduction
The CMG-RTM is a battery backed, high-precision, thermally-compensated, real-time
clock module with simulated GPS output. It obtains its initial synchronisation from
a GPS receiver and, once locked, starts generating NMEA sentences and a PPS (pulse
per second) signal, making it suitable for use as a time-source for GPS-synchronised
equipment in situations where GPS receivers are impractical. A large liquid crystal
display provides status information.
Once the initial synchronisation source is removed, the CMG-RTM continues to run
under battery power, maintaining timing through the use of a high-precision,
thermally-compensated, crystal-controlled oscillator. The CMG-RTM can then be
transported to the deployment site and connected to a digitiser, from which it
subsequently draws power. Once powered, it will generate the NMEA and PPS
signals which are required to synchronise the connected digitiser.
Each unit is individually factory-trained to calculate a temperature compensation
table with 0.1°C granularity, ensuring stability of operation in a wide range of
environments.
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Operation
3 Operation
The CMG-RTM has two 10-pin bayonet connectors: one, on the right, for attachment
to a power supply (during synchronisation) or to a digitiser (during operation) and
one, on the left, for attachment to a GPS receiver.
If the unit has been disconnected from power for some time, the internal battery will
be discharged. The unit automatically shuts down under these circumstances.
The unit should first be connected to either a digitiser or power supply, using the
right-hand connector. The following screen will be displayed:
The second line shows the date and time, according to the internal clock. The third
line shows that no GPS data are currently being received.
A GPS receiver should then be attached to the left-hand connector.
The third line of the display will change to show that GPS signals are being received.
The GPS receiver produces two sets of outputs: a stream of textual data know as the
NMEA (because it is in NMEA 0183v1.5 format) and a one-Hertz pulse train known as
the PPS. The NMEA provides coarse timing (to the nearest second) and the PPS
provides accurate sub-second timing.
Both signals are required for correct operation. If either is missing, there is a
problem with the receiver, the cable or the CMG-RTM itself.
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Operation
If the NMEA is missing, the following screen is displayed:
If the PPS is missing, the following screen is displayed:
If you see either of these screens, please check the GPS cable and connections. If no
fault is apparent, please contact GSL technical support for advice.
While the GPS receiver is looking for satellite signals, the display will change:
In the illustration above, the receiver does not know where it is (No Fix) and it can
see no satellites (SVs stands for “Space Vehicles”, which is standard GPS
terminology for the satellites used by the GPS system). As a result, the system is not
synchronised (Not Sync).
Over the next minute or so, the receiver will start to receive data from more satellites.
It will first calculate an automatic two-dimensional fix (A2D). This is not sufficient
for synchronisation purposes and if this condition persists, the receiver should be
moved to obtain a better view of the sky. For more information about the GPS system
and optimum receiver placement, please see our GPS installation guide at
http://www.guralp.com/howtos/setting-up-gps-equipment.shtml.
When sufficient satellites have been in view for enough time, the GPS receiver will
establish a full three-dimensional fix (A3D) and the display will change to the
following:
Here, five satellites are in view (5 Svs).
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Operation
After a minute or so with a stable three-dimensional fix, the clock control system
will start the synchronisation process and the display will change to the following:
The internal clock will be coarsely adjusted until it is in line with the GPS time, and
then the offset (the difference between internal clock time and GPS time) and drift
(the first derivative of the offset) are monitored while the pulse width modulation
value is altered to minimise both. This process is known as training.
In the display above, the first line gives the drift, or frequency error (-5E-8) as -5×10-8.
Note that the drift value is unit-less, representing seconds per second. The third line
shows the elapsed time since synchronisation (0d00:03), which is zero days, zero
hours and three minutes, and the current offset from PPS, which is 12.3µs. The last
line shows the date and time.
The CMG-RTM should now be left until both offset and drift reach sensibly small values.
In a thermally stable environment with good satellite visibility, this process should take
less than an hour.
The GPS receiver and power supply (or digitiser) can then be disconnected. The display
will change to show that GPS data are no longer being received:
The second line shows the elapsed time since synchronisation (0d01:23) and the offset
from GPS time, which is now an estimate (EST). The bottom line shows the state of
charge of the internal battery. If the battery were fully charged, the display would look
like this:
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Operation
The unit can now be completely disconnected from external power. It enters a lowpower sleep mode, turns off the display back-light and stops transmitting GPS signals.
The display shows the time since synchronisation and the estimated offset from GPS
time; the date and time from the internal clock; the battery status; the sleep indicator and
the time during which it has been sleeping. If the battery is fully charged, the unit will
run for approximately eight days in this mode.
The unit is now free-running under battery power and can be transported to the
deployment site, where the target digitiser should be plugged into the right-hand
connector, which will then provide power. The CMG-RTM will provide accurate timing
to the digitiser.
Note: The CMG-RTM will not provide positional information to the
digitiser. Only timing information is generated.
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Connector pin-outs
4 Connector pin-outs
4.1 GPS Output, Power Input (right-hand connector)
This is a standard 10-pin, military-specification,
bayonet plug, conforming to MIL-DTL-26482 (formerly
MIL-C-26482). A typical part-number is 02E-12-10P
although the initial “02E” varies with manufacturer.
Suitable mating connectors have part-numbers like
***-12-10S and are available from Amphenol, ITT
Cannon and other manufacturers.
Pin
Function
A
Power 0 V input
B
Power +5 V to +36 V DC input
C
1pps signal output to digitiser
D
not connected
E
Console RS232 TxD (for factory use only)
F
Console RS232 RxD (for factory use only)
G
Ground (for factory use only)
H
not connected
J
not connected
K
NMEA RS232 transmit to digitiser
Wiring details for the compatible socket, ***-12-10S,
as seen from the cable end.
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Connector pin-outs
4.2 GPS Input (left-hand connector)
This is a standard 10-pin, military-specification,
bayonet plug, conforming to MIL-DTL-26482 (formerly
MIL-C-26482). A typical part-number is 02E-12-10P
although the initial “02E” varies with manufacturer.
Suitable mating connectors have part-numbers like
***-12-10S and are available from Amphenol, ITT
Cannon and other manufacturers.
Pin
Function
A
Power 0 V output
B
Power +V output
C
1pps signal input
D
not connected
E
not connected
F
not connected
G
Ground
H
not connected
J
not connected
K
NMEA RS232 receive from GPS
Wiring details for the compatible socket, ***-12-10S,
as seen from the cable end.
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Specifications
5 Specifications
Physical
Length (casing)
150 mm
Length (including connectors)
162 mm
Width
80 mm
Depth
45 mm
Material
Polystyrene
Display
21 character, 4 line
Weight
305 g
Electrical
Power supply input voltage
5 V to 36 V DC
Power supply input current
(without receiver connected)
20 mA at 12 V DC
Battery capacity
1.84 Ah
Battery backup
7 – 10 days
Timing
NMEA output sentences
$GPGSA and $GPZDA
Trained Temperature range
-10 °C to +50 °C
in 1 °C increments
(extrapolated for out-of-range values).
Operating Temperature range
-10 °C to +60 °C *
* Battery and display performance are
both compromised at the extremes of this
range but timing performance is
unaffected.
Accuracy
<3×10-8
(<100 ms per month)
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Revision history
6 Revision history
2015-03-31
2015-04-15
2016-03-10
MAN-RTM-0003
A
B
New document
Revised graphics and improved specifications
Facelift with no significant content changes
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