SYNCHRONIZING THE SYNCHRONIZING THE COMPUTER CLOCKCOMPUTER CLOCK

Who Should Synchronize?Who Should Synchronize?

• Recommended Recommended onlyonly if you have another computer system if you have another computer system delivering datagrams with UTC time stamps.delivering datagrams with UTC time stamps.

• Among the systems requiring time synchronization:Among the systems requiring time synchronization:– POS MV/Octopus F180 (Delayed Heave)POS MV/Octopus F180 (Delayed Heave)– Atlas Fansweep 20Atlas Fansweep 20– Simrad EMSimrad EM– Reson 7125Reson 7125– R2SonicR2Sonic– GeoswathGeoswath– Elac Seabeam Elac Seabeam – Tritech Sea KingTritech Sea King– Benthos C3DBenthos C3D

Clock Synchronization: Clock Synchronization: How it worksHow it works

When the ZDA sentence arrives: (1 Hz only!)When the ZDA sentence arrives: (1 Hz only!) HYPACK SURVEY compares the UTC time from the GPS (corrected HYPACK SURVEY compares the UTC time from the GPS (corrected

with the time zone offset) with the time from the VERITIME clock with the time zone offset) with the time from the VERITIME clock model (HYPACK SURVEY).model (HYPACK SURVEY).

It can speed up the VERITIME clock model, or slow it down so that it It can speed up the VERITIME clock model, or slow it down so that it matches UTC.matches UTC.

You should wait one or two minutes after starting HYPACK SURVEY You should wait one or two minutes after starting HYPACK SURVEY before starting to survey to allow the VERITIME clock model to before starting to survey to allow the VERITIME clock model to synch to UTC.synch to UTC.

When the GGA sentence arrives (any rate):When the GGA sentence arrives (any rate): HYPACK SURVEY uses the time tag in the GGA sentence (corrected HYPACK SURVEY uses the time tag in the GGA sentence (corrected

for local time zone offset) as the position time tag.for local time zone offset) as the position time tag.

When a message arrives from your echosounder, When a message arrives from your echosounder, MRU or other non-GPS device:MRU or other non-GPS device:

HYPACK SURVEY gets a time tag from the VERITIME clock model, HYPACK SURVEY gets a time tag from the VERITIME clock model, which has been ‘synched’ to UTC less the local time zone offset.which has been ‘synched’ to UTC less the local time zone offset.

Clock Synchronization – Part IIClock Synchronization – Part II

• Clock synchronization Clock synchronization is only available when using the is only available when using the GPS.DLL, GPS.DLL, thethe POSMV.DLL, POSMV.DLL, and the and the F180.DLL.F180.DLL.

• GGA and GGK sentences contain their UTC measurement time.GGA and GGK sentences contain their UTC measurement time.• These times are adjusted to local time zone, along with any latency offset These times are adjusted to local time zone, along with any latency offset

entered by the user and used as the time tag for the position.entered by the user and used as the time tag for the position.

Device MessageDevice Message Veritime ActionVeritime Action Time TagTime Tag

‘‘ZDA’ from GPSZDA’ from GPS VERITIME Clock VERITIME Clock Model AdjustedModel Adjusted

Difference recorded Difference recorded in RAW recordin RAW record

‘‘GGA’ or ‘GGK’ from GGA’ or ‘GGK’ from GPSGPS

NothingNothing From GGA/GGK From GGA/GGK sentencesentence

Echosounder, gyro Echosounder, gyro and other devicesand other devices

NothingNothing From VERITIME From VERITIME modelmodel

Clock Synchronization – Part III Clock Synchronization – Part III 1PPS Box1PPS Box

GPS

ComputerRS-232 Out (GGA, VTG, ZDA)RS-232 Out (GGA, VTG, ZDA)

GPS ComputerRS-232 Out (GGA, VTG, ZDA)RS-232 Out (GGA, VTG, ZDA)

1PPS Box

1 PPS Out1 PPS Out

RS-232 Out (GGA, RS-232 Out (GGA, VTG, ZDA)VTG, ZDA)

With 1PPS Info on With 1PPS Info on CTS LineCTS Line

Without 1 PPS BoxWithout 1 PPS Box

With 1 PPS BoxWith 1 PPS Box

12VDC

Without a 1PPS Box:Without a 1PPS Box: Time of ZDA sentence is based on the arrival of Time of ZDA sentence is based on the arrival of first character of ZDA transmission. first character of ZDA transmission.

With a 1PPS Box:With a 1PPS Box: Time of ZDA sentence is based on arrival of 1PPS Time of ZDA sentence is based on arrival of 1PPS pulse. pulse.

The 1 PPS BoxThe 1 PPS Box

12VDC In12VDC In

RS232 Out RS232 Out (to computer)(to computer)

1 PPS In 1 PPS In

(from GPS) (from GPS) BNC BNC

ConnectorConnector

RS232 InRS232 In

(from GPS) (from GPS) Requires ZDA at 1 Hz Requires ZDA at 1 Hz May also carry 1PPS May also carry 1PPS

pulse on Pin 8 or 9pulse on Pin 8 or 9

1 PPS Receipt 1 PPS Receipt StrobeStrobe

Alternates Alternates REDRED//GREENGREEN every 1 every 1

second when second when operating correctlyoperating correctly

Time Synchronization TestsTime Synchronization Tests

Make sure you Make sure you monitor the monitor the difference between difference between the VERITIME and the VERITIME and GPS clocks!GPS clocks!

The difference The difference should be small should be small (<20mSec) and (<20mSec) and should work its way should work its way towards 0.0 after a towards 0.0 after a spike.spike.

If it gets large and If it gets large and stays large, stays large, something is wrong.something is wrong. Stop SURVEY.Stop SURVEY. Figure it outFigure it out !!!!

ZDA OnlyZDA Only

ZDA and 1 PPS BoxZDA and 1 PPS Box

Synch the Computer Clock: Synch the Computer Clock: HARDWARE SettingsHARDWARE Settings

Select ONE GPS device to use to synchronize the computer clock to UTC in the HYPACK Configuration page.

1PPS Configuration: 1PPS Configuration: Settings in the GPS.DLLSettings in the GPS.DLL

Always Display the Always Display the Synchronization Synchronization GraphGraph

Specify use of a Specify use of a 1PPS box (under 1PPS box (under Setup).Setup).

ZDA – 1PPS Testing: ZDA – 1PPS Testing: Utilities - Calibration - ZDA TESTUtilities - Calibration - ZDA TEST

Provides a test of the consistency of your ZDA message for Provides a test of the consistency of your ZDA message for synchronization.synchronization.

Located under ‘Utilities – Calibration’ menu item.Located under ‘Utilities – Calibration’ menu item.

Graph shows ‘Sync Error’ in mSecs. Sync Error equals the difference Graph shows ‘Sync Error’ in mSecs. Sync Error equals the difference between VERITIME and the time of arrival of the ZDA messagebetween VERITIME and the time of arrival of the ZDA message