MODUS SVS Sound Velocity Sensor Section 2 - Software

© Valeport Limited
MODUS SVS Sound Velocity Sensor
Section 2 - Software Operation
MODUS SVS Operating Manual
Section 2, Page 1
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© Valeport Limited
CHAPTER
DESCRIPTION
PAGE
1 INTRODUCTION.................................................................................................................................4
1.1 Installation
4
2 OPENING DATALOG 400...................................................................................................................5
3 ESTABLISHING COMMUNICATIONS.................................................................................................6
4 INSTRUMENT SETUP...........................................................................................................................8
4.1 Standard
8
4.1.1 Set Button
8
4.1.2 Pressure Tare Setting............................................................................................................9
4.1.3 Quick Setup 10
4.1.3.1 Saving a Quick Setup Regime....................................................................................10
4.1.3.2 Selecting a Quick Setup Regime................................................................................10
4.1.4 Sampling Modes & Patterns...............................................................................................10
4.1.4.1 Single Mode...............................................................................................................11
4.1.4.2 Hold Mode 11
4.1.4.3 Continuous Mode......................................................................................................12
4.1.4.4 Trip Mode 12
4.1.4.5 Burst Mode 13
4.1.4.6 CMA (Continuous Moving Average)..........................................................................14
4.1.5 Output Mode 15
4.1.5.1 Valeport
15
4.1.5.2 AML
16
4.1.5.3 CSV
16
4.1.5.4 SVP16
16
4.1.5.5 NMEA
17
4.1.5.6 WESTGEO 17
4.1.5.7 HYPACK 17
4.1.5.8 SEABIRD 17
4.2 Sensor Setup 18
4.2.1 Trip Mode
19
4.2.2 Tare Option 19
4.2.3 User Calibration.................................................................................................................20
4.3 Advanced
21
4.3.1 Output Separator................................................................................................................21
4.3.2 Local Conditions................................................................................................................21
5 RUNNING THE INSTRUMENT..........................................................................................................22
5.1 Software Switch On ..................................................................................................................22
5.1.1 Method 1
22
5.1.2 Method 2
22
5.1.3 Run
22
5.2 Real Time Data 23
5.2.1 Real Time Data Logging.....................................................................................................23
5.2.2 Select Max Viewable Data Points......................................................................................23
5.2.3 AML Emulation Mode........................................................................................................24
6 DATA VIEWING 25
6.1 Opening Stored Data Files.........................................................................................................25
6.2 Simple Display 26
6.3 Scroll Display 27
6.4 Graphical Display......................................................................................................................28
6.4.1 Scroll & Focus....................................................................................................................31
6.4.2 Rotate
32
6.4.3 Move
32
6.4.4 Zoom
33
6.4.5 Depth
33
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7 CALCULATION 34
8 ABOUT
35
9 CALCULATION FORMULAE..............................................................................................................36
9.1 SAlinity
36
9.2 Density Anomaly Gamma.........................................................................................................38
9.3 Speed Of Sound........................................................................................................................39
9.3.1 Standard Formulae............................................................................................................40
9.3.1.1 Pressure/Depth Relationship......................................................................................40
9.3.1.2 Wood (1949).............................................................................................................40
9.3.1.3 Wilson (October 1960)..............................................................................................41
9.3.1.4 Medwin (1975).........................................................................................................42
9.3.1.5 Chen and Millero (1977)...........................................................................................43
9.3.1.6 Del Grosso (1974)......................................................................................................44
9.3.1.7 MacKenzie (1981).....................................................................................................45
9.3.2 Discussion 46
9.3.2.1 Development of Formulae.........................................................................................46
9.3.2.2 Comparison of Formulae...........................................................................................46
9.3.2.3 The Pressure/Depth Algorithm...................................................................................47
9.3.3 Conclusions 48
10 APPENDIX 1 CONFIGURATION CODES.......................................................................................49
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1
INTRODUCTION
DataLog 400 is the user interface program supplied with all 400 Series systems from Valeport Ltd,
including the MODUS SVS Sound Velocity Sensor. The program is written in Delphi, and will run on all
PCs operating Windows 95 or above. As is the nature of all software, the faster the computer, the better
the software will perform. As an absolute minimum, we recommend the following PC specification:
•
•
•
•
•
Pentium 100MHz (or equivalent)
32Mbyte RAM
CDROM Drive
1 spare comm port
100Mbyte Disk Space
Note that installation of DataLog 400 itself requires only 5.4Mbyte of disk space. However, Windows will
utilise a large amount of disk space as “virtual memory” (upwards of 20Mbyte), which must be taken into
account.
This manual will guide the operator through all the functions that DataLog 400 and the MODUS SVS have
to offer, including the wide variety of sampling regimes and data viewing. Please note that although
DataLog 400 offers a variety of data display modes, users may wish to utilise a standard spreadsheet
package such as Microsoft Excel for data manipulation.
The MODUS SVS has no capability for internal data storage, or “logging”, only for real time data output.
Any references in this manual to internal data logging or data upload do not relate to this product, but to
other Valeport instruments that also operate with the DataLog 400 software. The capability to record
real time data output on the operating PC is retained.
1.1 INSTALLATION
As with all installation programs, we recommend that all other applications be closed before commencing
installation.
DataLog 400 is supplied on a single CDROM. It does not feature an Auto-run facility, so users will be
required to insert the CDROM into their CD drive, and run the Setup.exe program manually. This can be
done either by selecting Run from the Start menu, and browsing for the Setup.exe file under the CD drive
(typically drive D or E), or by clicking on the Setup.exe program under the CD drive in Windows Explorer.
The Setup.exe program will launch a wizard that will guide the user through the remainder of the
installation process. By default, the installation program will create a new directory in which to install
DataLog 400, although you may change this if you wish:
C:\Program Files\DataLog 400
On completion of installation, a window will appear with a shortcut icon to
the program. This may be dragged onto the desktop if required:
Note that DataLog 400 software is distributed free with the equipment – therefore no password or software
key is required for installation.
To Run the software, simply double click the Desktop icon. The following pages describe the operation of
the software.
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2
OPENING DATALOG 400
Double clicking the desktop icon (
), or running the DataLog 400.exe program through Windows
Explorer, will reveal the following screen, which allows access to all major DataLog 400 functions. Note
that all features are accessed through a selection of tabs at the top of the page – there is no menu bar. Also
note that at any point in the software, only tabs which are relevant will be visible. The Calculation and
About tabs, which are less important in terms of instrument operation and data viewing, are covered in
later Chapters.
If the user wishes to close down DataLog 400 at any time, simply
click on the Exit button:
If for any reason communications are lost, the “Stop Trying” button
may be used. Clicking on this button will return the user to this
point in the software:
The major functions that DataLog 400 will allow at this point are as follows. Each function is described
fully at subsequent chapters in this manual. Note also the section of the screen titled “Real Time Data”.
Please refer to Chapter 5 for details of this section.
Establishes communications with the instrument, and causes the unit to wait for
further instructions. See Chapter 3.
Puts the instrument into Run mode. This button should only be used if the user is
confident of the current instrument settings. See Chapter 5.
View an existing data file, either previously uploaded and translated, or
saved from the real time output. See Chapter 7.
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3
ESTABLISHING COMMUNICATIONS
After connecting the instrument to the PC using
the 500mm Y lead as described in Section 1 of
this manual, the first step in establishing
communications with the instrument is to select
the correct communications (comm) port. A
drop down menu allows the user to select from
up to 4 available comm ports.
Selecting the incorrect comm port is the most
likely reason for any failure to communicate.
Note that all Valeport 400 Series instruments (i.e. instruments designed to work with DataLog 400) are
fitted with three standard digital data outputs – RS232, RS485 and RS422. The larger “MIDAS” instruments
also have one optional output, FSK modem. This option is not available on the smaller “Monitor” &
“MODUS” instruments. RS232 format can be read directly by a PC comm port. If using any of the other
methods, the PC will need to be fitted with a suitable interface, which will either be a special adaptor unit
supplied by Valeport, or in the form of an additional circuit board added to the PC. If using RS485 or FSK
communications, please check the box next to the comm port selection box. This will slightly alter the
protocol that DataLog 400 uses to communicate with the instrument (note that FSK comms defaults to
19200 baud rate). It is important that the boxes are left unchecked if just standard RS232 communications
or RS422 communications are being used.
The next step in establishing communications is
to select the required baud rate. Note : The
MODUS SVS will only work at up to 38400
baud.
The instrument will automatically detect which
baud rate is being used, but note that the longer
the cable being used, the slower the rate that
will be required. A guide to suitable baud rates
is given in the drop down menu. Note also that
even some new PCs may be fitted with low
quality comm ports – users may find that a lower baud rate is necessary.
Next, ensure that the power supply is turned on.
All Valeport 400 Series instruments (i.e. instruments designed to work with DataLog 400) can be
interrupted at any point during their operation, whether they are actually in the process of sampling or in a
sleep mode between bursts.
Finally, click on the Interrupt button:
During operation, DataLog 400 will show the current status of the software at the bottom of the screen:
The left hand section shows the software status, the centre section shows the last response from the
instrument, and the right hand section shows the PC date and time.
The Autobauding procedure by which the instrument detects which baud rate is being used may take up to
15 seconds to complete – please be patient while the software shows “Attempting to Communicate”. After
the baud rate has been established, the instrument will send various pieces of information to the software,
including Serial Number, type and number of sensors fitted, current sampling setup and so on. Again, this
may take some seconds to complete, so please be patient!
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Once DataLog 400 has communicated with the instrument, an information screen appears detailing
connection information, and basic sensor information such as serial number, code and name of all fitted
sensors, and software version. To clear this screen, simply click on OK.
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4
INSTRUMENT SETUP
Once the Connection Data screen has been cleared, the Sampling Setup page will appear.
The Sampling Setup tab allows the user to set the instrument’s sampling regime. The MODUS SVS will
allow six different sampling modes. There are four sub-menus, labelled Standard, Sensor Setup, Advanced
and Instrument Settings.
4.1 STANDARD
This page gives acces to all the basic setup functions required to control the instrument operation – The
more advanced setup features are accessed through the Sensor Setup and Advanced tabs.
DataLog 400 will only allow the user to set sampling parameters relevant to the selected mode – for
example, in continuous sampling mode (CONT, above), the user is not required to select an interval for
BURST sampling, so that section is not displayed. Later pages explain the different sampling patterns
available, and show the parameters which the user will need to set for each mode. However, there are
some functions which apply to all sampling modes, and these are discussed first:
4.1.1
SET BUTTON
Any parameters
which are
changed in this
screen will not
be sent to the instrument unless the SET button is
pressed, with the exception of Pressure Tare
Setting and Set Time.
MODUS SVS Operating Manual
If the user leaves this
screen without
confirming any
changes with the SET
button then the
following warning
will be displayed:
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4.1.2
PRESSURE TARE SETTING
The user may wish to set a Pressure Tare value. In underwater instruments, pressure sensors are usually of
the absolute type – that is to say, they measure the total pressure exerted on the transducer face, including
atmospheric pressure.
It is often the case that the user wishes to disregard the atmospheric pressure, particularly in short term
deployments where it is unlikely to change significantly over the deployment period. If this is the case,
then a Tare value can be set. This is done by positioning the instrument at sea level, and taking a pressure
reading. This reading is recorded in the instrument as being the atmospheric pressure at time of
deployment, and may be subtracted from all subsequent pressure readings.
Press the Set Pressure Tare button to take a Pressure Tare reading. The
current Pressure Tare value is indicated in the text box below the button.
Alternatively, the user may enter their own desired value for the Pressure
Tare by simply typing in the text box and then clicking the Set Pressure
Tare button. This is particularly useful for resetting the Tare value to
zero.
Having taken a Pressure Tare reading, the user still has the choice of whether or not to actually subtract
this value from the subsequent pressure readings, or just keep it as a record of the atmospheric pressure at
time of deployment. Please refer to the Sensor Setup tab to confirm whether the Tare value should actually
be used or not (Chapter 4.2.2)
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4.1.3
QUICK SETUP
Many work schedules require that standard customer specified sampling regimes are used. To allow for
this, DataLog 400 will store up to three such regimes, as well as Valeport’s own factory default setup.
4.1.3.1
SAVING A QUICK SETUP REGIME
Select one of the Customer Setup buttons as shown. Then setup the
required sampling regime – note that all setup parameters are recorded,
with the exception of the Pressure Tare value. When the screen shows
the required sampling regime, click on the Save Current Setup button.
The displayed setup will be recorded under whichever Customer Setup
button is currently highlighted.
NB: Save Current Setup BEFORE using the SET button.
Note that the user cannot alter the Valeport Setup configuration.
4.1.3.2
SELECTING A QUICK SETUP REGIME.
Simply select any of the four Quick Setup buttons. The screen will automatically display the saved Setup.
Then simply click on the SET button to confirm.
4.1.4
SAMPLING MODES & PATTERNS
The MODUS SVS has 6 different basic sampling modes. These are explained in detail over the next few
pages.
One of the key features of the MODUS SVS (and indeed all other Valeport 400 Series instruments) is the
synchronised sampling pattern. Most other similar products on the market (including older Valeport
products) sample the fitted sensors in sequence – that is to say, the microprocessor samples data from
Sensor 1, then Sensor 2, then Sensor 3 etc., before repeating the sequence. As technology advances, these
sampling sequences are becoming more and more rapid, but they still result in non-synchronised data.
The Valeport system works differently. It sends a single command to all fitted sensors at exactly the same
time, meaning that each sensor samples at exactly the same time. The microprocessor then collects data
from the sensors to produce the full data record. This pattern is repeated up to 8 times per second, and the
result is absolutely synchronised data. This synchronised sampling pattern is a feature of all the sampling
modes available.
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To select a sampling mode, simply highlight the required mode in the drop down menu under Sampling
Parameters, as shown:
4.1.4.1
SINGLE MODE
The Single sampling mode means that when the unit is set to Run, it takes a single measurement of all
parameters fitted, and outputs the single data string in real time. This operation will happen every time the
Run command is sent to the instrument (Run command is described in Chapter 5.1.3)
When using the Single mode, no other functions under the Sampling Parameters section are required, and
are therefore not visible.
4.1.4.2
HOLD MODE
Hold mode is similar to Single in that it will take a single set of measurements each time the Run
command is used. However, the data is held in instrument RAM until requested by a separate command
(Get Held Data command is described in Chapter 5.1.3.2).
Again, no other functions need be set under Sampling Parameters.
In Hold mode, data is only available in real time. Data may, however, be recorded on PC as described in
Chapter 5.2.1.
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4.1.4.3
CONTINUOUS MODE
Continuous Mode (CONT) causes the instrument to sample data at a
fixed rate until it is interrupted, or power is removed. As can be seen,
the user is also required to select the sampling rate.
All data is available in Real Time.
4.1.4.4
TRIP MODE
Trip mode is an event triggered mode, typically used during profiling. In this mode, data will be sampled
only once a trigger value on a chosen sensor has been reached, and then again at regular incremental
changes of that parameter. A good example is using a Pressure Trip on a profile. The instrument may be
set to monitor the Pressure sensor, and when the output reaches the Trip Level (i.e. the instrument reaches
a certain depth), sampling will begin. Subsequent samples will then be taken every time the pressure
changes (i.e. instrument descends or ascends) by the Trip Increment (maximum sampling rate is 8Hz).
When Trip mode is selected, a separate section of the screen will become visible, showing the Trip
Parameter (Pressure in this case), Trip Level, and Trip Increment. In the above screen, the Trip Level is 12
dBar (approx 12m), and the Trip Increment is 0.25dBar (approx 0.25m). Note that the Trip Level takes
account of any pressure tare that has been set.
The user should simply type the desired Trip Level and Trip Increment values in the text boxes.
Note that use of the Trip mode is not restricted to the Pressure Sensor, even though it is the most
commonly used. Any sensor fitted to the instrument may be used as the Trip Parameter; the desired sensor
may be selected in the Sensor Setup screen (Chapter 4.2).
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4.1.4.5
BURST MODE
Burst Mode offers the user the greatest flexibility in sampling setup. Generally speaking, the sampling
programme causes the instrument to take a set number of samples at a chosen rate, then go into sleep
mode for a defined period of time before waking up and repeating the sequence. The user may set the
desired sampling rate, the number of samples in the burst, and the interval between bursts. In this way, the
deployment time of the instrument may be greatly extended. Burst mode is particularly suitable for long
term studies, where specific parameters do not change rapidly and overall trends are more significant.
Parameters that the user must set are therefore:
Sample Rate
Select 1, 2, 4 or 8Hz from the drop down menu
Period
This is the number of samples in the Burst (minimum 1).
In this example, 20 samples at 4 Hz will take 5 seconds.
Interval
This is how often a burst will occur, in seconds. Note
that the instrument requires a minimum of 20 seconds
between the end of one burst and the start of the next –
DataLog 400 will not allow an interval less than this to
be set. If the user tries to set a shorter interval than this,
the minimum interval possible with the present Sampling
Rate and Period will be entered automatically.
Average Type
Finally, the user has a choice of three data averaging
modes, which require further explanation:
When using Burst mode, the MODUS SVS is capable of calculating the mean value of data during a
measurement burst, for each parameter fitted. The user has the following options:
NONE
No data averaging is performed over the burst. The instrument will log and output every
measurement made during the burst.
FIXED
The instrument will wait until the end of the burst, and will then calculate the mean value of
each parameter over the burst. If the burst is cut short by the user attempting to communicate
with the instrument, then the average of that burst will be calculated as the mean of all
measurements that were made.
MOVING
The user can also create a Moving Average window. A new
text box will appear asking the user to choose the moving
average length required, which may be any number up to the
number of samples in the burst. The instrument will log and
output the mean value of the previous ‘x’ measurements made
in the burst, where ‘x’ is the Moving Average length. The
output will be updated with every sample until the end of the
burst. For example, in the above screen, if a Moving Average length of 5 samples were set,
the output would be as follows:
Sample No.
1
2
3
4
Output
Mean of Sample 1
Mean of Samples 1,2
Mean of Samples 1,2,3
Mean of Samples 1,2,3,4
Sample No.
5
6
19
20
Output
Mean of Samples 1,2,3,4,5
Mean of Samples 2,3,4,5,6
Mean of Samples 15,16,17,18,19
Mean of Samples 16,17,18,19,20
Finally, if either the Fixed or Moving Average option is selected, the instrument will also calculate the
Standard Deviation of the data. This value will always be output in real time, but the user may decide that
in order to conserve memory, it does not need to be logged.
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4.1.4.6
CMA (CONTINUOUS MOVING AVERAGE)
This mode is a specific configuration of the Burst mode, where data is
output continuously. Users may wish to use this output instead of the
standard Continuous mode if data averaging or Standard Deviation data
is required.
The user is simply required to enter the Sample Rate (1,2,4 or 8Hz), and
the length of the Moving Average window in samples.
In this mode, the instrument will run indefinitely, always outputting the
mean of the last ‘x’ samples, where ‘x’ is the number of samples in the
Moving Average window.
Note that a continuous moving average regime can be setup manually by
the user using the Burst mode. This mode is simply a shortcut to such a
setup.
Note also that the instrument interprets CMA mode as a Burst mode. If an
instrument is setup in CMA mode, the sampling regime will be recorded in
the instrument as a Burst mode. This means that when the instrument is
subsequently interrogated, the screen will show that the instrument is set in
Burst mode, as shown left.
Note that the screen shows the key points for setting a Continuous Moving
Average manually:
1. The sampling period must be the same as the sampling rate, giving a
duration of 1 second.
2. The Sampling Interval must be set to 1 second.
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4.1.5
OUTPUT MODE
A feature of the MODUS SVS is its ability to emulate data output
formats of other manufacturer’s sensors. This feature is included to
allow the MODUS SVS to be easily swapped for existing sensors, and
to give compatibility with third party loggers and instrumentation.
DataLog 400 is only capable of displaying data which is generated
in Valeport’s own output mode, but it may be used to setup the sensor in these other modes.
Available output modes, together with descriptions are below. Note that the MODUS SVS also has
a separate mode for total emulation of an Applied Microsystems Ltd Smart Sensor, in which the
instrument will respond to AML type commands as well as output data in that format. This mode
is settable through a Terminal program such as Hyperterminal (section 5.2.3), and is distinct from
the AML Output mode as set in this section, which only causes data to be output in AML mode,
with all commands remaining as standard Valeport commands.
4.1.5.1
VALEPORT
This is the factory set Valeport output mode. Data output in this mode may be viewed by DataLog
400.
1484.401<space>M/SEC
1484.402<space>M/SEC
1484.401<space>M/SEC
Or, if pressure sensor fitted:
1484.401<space>M/SEC<space>0001.00<space>DBAR
1484.402<space>M/SEC<space>0001.10<space>DBAR
1484.401<space>M/SEC<space>0001.20<space>DBAR
If the unit is running in Burst sample mode, the output string will include the standard deviation
after each parameter, as follows:
1484.401<space>M/SEC<space>0.001
1484.402<space>M/SEC<space>0.001
1484.401<space>M/SEC<space>0.002
Or, if pressure sensor fitted:
1484.401<space>M/SEC<space>0.001<space>0001.00<space>DBAR<space>0.050
1484.402<space>M/SEC<space>0.001<space>0001.10<space>DBAR<space>0.061
1484.401<space>M/SEC<space>0.002<space>0001.20<space>DBAR<space>0.042
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4.1.5.2
AML
The data is output in the format of the Applied Microsystems ltd “Smart Sensor”, as a six-digit
number. Sound velocity is in metres / second expressed as the following format: XXXX.XX followed
by a carriage return and line feed:
1503.21
1503.25
1503.26
4.1.5.3
CSV
CSV output (Comma Separated Variable) is:
mm/dd/yy, hh:mm:ss, VVVV.V,D.D,TT.T
VVVV.V is the sound velocity data, D.D is the measurement depth for each record, and TT.T is the
unit temperature. Since this format is a simulation of a standard output, temperature must be
included in the string. However, the Modus SVS contains no temperature sensor, so this value is
fixed at 00.0.
A typical output would therefore look like:
04/20/00, 15:36:20, 1506.2,2.0,00.0
04/20/00, 15:36:20, 1506.3,2.5,00.0
04/20/00, 15:36:21, 1506.2,3.0,00.0
04/20/00, 15:36:21, 1506.1,3.5,00.0
4.1.5.4
SVP16
This configuration outputs the data in the same format as the Applied Microsystems Ltd SVP16
Sound Velocity Profiler.
“CALC, DBxxxx, 09/16/99, 1, Meters”
OHSI Sound Velocity Profiler S/N DBxxxx
Date: 99259 Time: 1133
Depth Offset (M): 0
Depth (M) Velocity (M/S) Temp (C)
1.5 1503.0 8.5
2.0 1504.2 9.0
2.5 1504.4 9.0
xxxx signifies the serial number of the instrument. In the first line of the header, the date format is
mm/dd/yy, and in the third line of the header it is yyddd, where ddd is the Julian day.
The header is included at the start of the output to allow the data to be compatible with certain
third party devices.
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4.1.5.5
NMEA
This output string complies with the sentence structure of the NMEA standard for manufacturers
proprietary strings.
$PSSV, 1503.0, 1.5,M*54 (for Units = Meters)
$PSSV, 4860.0, 4.0,F*52 (for Units = feet)
The “$” character denotes start of sentence.
“P” Proprietary sentence ID
“SSV” Manufacturer’s mnemonic code
“,” The comma delimiter character starts each field except address and checksum
<ccc> Velocity, Depth, Measurement units data fields
“*” Checksum delimiter
<Checksum field> The absolute value calculated by exclusive-OR’ing the 8 data bits of each
character in the sentence between, but not including the “$” and “*”.
<CR><LF> End of sentence
4.1.5.6
WESTGEO
This sentence complies with the requirements of the current WG-1100 velocimeter output string.
634 01503
635 01503
636 01504
The string is composed of a 3-digit sequential event number, followed by a space, and then 5
characters of velocity data. Each record is delimited by a <CR><LF>.
4.1.5.7
HYPACK
Selection of the Hypack SV Format causes the sensor to output a header: FTP New followed by the
cast data in two columns (depth velocity). All readings are in meters.
FTP New
002.5 1500.0
003.0 1503.1
003.5 1503.2
4.1.5.8
SEABIRD
The MODUS SVS can also output data in the format of a Seabird CTD probe. The data has no
header information.
<LF><tab>TTT.TTTT,CC.CCCCC,PPPP.PPP,SSSS.SSSS,VVVVV.VVV<CR>
where,
TTT.TTTT = Temperature in Celsius
CC.CCCCC = Conductivity Siemens per meter
PPPP.PPP = Pressure in Decibars
SSSS.SSSS = Salinity in Parts per Thousand
VVVVV.VVV = Sound Velocity in Meter per second
Parameters which are not measured by the SoundBar are output as zeros.
Note that DataLog 400 is not able to display data in formats other than Valeport format.
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4.2 SENSOR SETUP
The Sensor Setup screen gives the user access to certain controls that are applicable to individual sensors
rather than the instrument as a whole. For example, the user may add their own calibration and units to
any particular sensor, and control whether the pressure sensor is to be subjected to the Pressure Tare value
(See Chapter 4.1.2)
The screen shows a table listing all the sensors fitted to the instrument. The user should use the mouse to
highlight the sensor of interest – the chosen sensor will be displayed in the
text box in the centre of the screen. Once selected, the user may alter the
setup of that particular sensor, as detailed on the following page:
If the user makes any changes to an individual sensor setup, these changes
must be confirmed by clicking on the Sensor Setup button. This button
must be pressed for each sensor – if a second sensor is selected before this
button is pressed, then the changes to the first sensor will not be sent to the
instrument. A warning message will confirm this.
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4.2.1
TRIP MODE
As described in Chapter 4.1.4.4, the MODUS SVS can be programmed to operate in a TRIP mode, where
regular changes in output from a particular parameter will cause data to be sampled. There are two types
of trip mode, Absolute and Relative:
Absolute
This should be used where the selected parameter will be
changing from zero (or another known value), for example, a
pressure based profile through the water column. The pressure
sensor will be reading zero at sea level, and the output will
increase as the instrument is lowered through the water column.
Also, the user is able to select whether the Trip Level will be
reached as data Increases or Decreases. Select the required
direction using the drop down menu. For standard pressure
profile, the Direction should be set to INCREASE.
Relative
This should be used where the initial value of the Trip parameter is
unknown. For example, the user may wish to take a reading
whenever the temperature of the water changes by 0.1°C.
However, the temperature of the water will not be known until the
instrument begins sampling. The relative trip function will therefore use the first
measurement as its baseline, and refer the trip increment to this initial reading. Neither Trip
Direction nor Trip Level (standard setup screen) are required if RELATIVE trip mode is set, and
are therefore not visible.
Note that only one parameter may be selected for use as a Trip sensor – as soon as another sensor has a
Trip mode assigned to it, the currently selected Trip Sensor will cease to be so.
4.2.2
TARE OPTION
As mentioned previously the user has the option to decide whether or not
the pressure sensor is subjected to the Pressure Tare value. The pressure
sensor will show either TARE or NOT_TARE in the right hand column. To
change this, simply highlight the sensor, and select either TARE or
NOT_TARE in the section at the right hand side of the screen. Note that this
section of the screen is only visibly when the Pressure sensor is selected.
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4.2.3
USER CALIBRATION
Data from all sensors on the MODUS SVS is output in calibrated format – however, the calibrations are
factory set. If the user wishes to input their own calibration data, or even change the units in which the
data is presented, this can be done by means of a secondary calibration (or USER calibration).
To enter the new required units, simply type into the Set User Units text box (all characters will be stored
in CAPITALS).
The new calibration string must be entered in a specific format. First of all, the user must determine the
equation that will convert the standard output format into the desired units. A good example is converting
pressure data in deciBar (DBAR) into data in metres. This can be performed to a good level of
approximation by a quadratic equation:
y = 2 * 10 −6 x 2 + 0.9943x
The instrument will accept up to a fifth order polynomial equation as a secondary calibration:
y = ax 5 + bx 4 + cx 3 + dx 2 + ex + f
The calibration string must be entered in the format
15;a;b;c;d;e;f
The format of the secondary calibration string for converting deciBars to metres is therefore:
15;0;0;0;2e-6;0.9943;0
NB: The initial figure 15 indicates to the instrument that the following information is a calibration string.
It must be included in the string. Note that the separators are all semi-colons (;). The instrument assumes
that all equations are fifth order polynomials – blank values must therefore be padded out with zeros.
Since data from Pressure sensors is often required in metres or
feet, these secondary calibrations are included as options in a
pull down menu (visible only when selected sensor is a Pressure
sensor).
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4.3 ADVANCED
The Advanced page of the Sampling Setup tab is laid out as shown. Note that any changes made in this
page:
page must be confirmed by using the Set button in the Standard page
4.3.1
OUTPUT SEPARATOR
The standard data strings from the MODUS SVS are output in the format of tab separated data, that is to say
each data value is separated from the next by a TAB. However, the user may
wish to use an alternative separator so that data is compatible with other
systems. A choice of separators is available, selectable from the drop down
menu. Choose between:
TAB
SPACE
: (colon)
; (semi-colon)
, (comma)
_ (underbar)
4.3.2
LOCAL CONDITIONS
These values are included for reference only, and are not included in any
onboard calculations. The Gravity value shown is the local Gravity at
Valeport’s premises in m/s². The Density value is the Density of Standard
Seawater at 35 Salinity and 15°C. The user may alter these values if required
by simply typing in the text boxes.
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5
RUNNING THE INSTRUMENT
Once the user has set the instrument up as required, the instrument may be set into Run mode. There are
two methods of doing this:
5.1 SOFTWARE SWITCH ON
5.1.1
METHOD 1
If the user is confident of the current instrument settings, and wishes to Run the
instrument whilst it is connected to PC, then the Run button may be pressed as
soon as DataLog 400 is opened. The software will communicate with the
instrument automatically, in order to determine which sensors are fitted, and in
which mode the instrument is set up.
5.1.2
METHOD 2
If the user has used the Interrupt button to communicate with the instrument, and subsequently viewed
and/or Set the sampling regime, then the Communicate tab to should be selected to allow access to the
Run button.
5.1.3
RUN
Note that once DataLog 400 has established communications
with the instrument, a separate section will become visible in the
Communicate screen, indicating some brief details about the
current setup. Users will only notice this once they press the
Run button, or when they return to the Communicate screen
after Setup.
As soon as the instrument is set into Run mode, DataLog 400 will
display this screen. The graphical display facility within the
software can plot any of the parameters against any of the other
parameters on the x axis, or against time. The user is required to
select which parameter should be used as the x axis before any
data viewing is possible. Then click on OK to proceed.
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What happens next depends on the sampling mode that has been selected:
Single Mode
Display screens will be updated every time the Run button is pressed.
Hold Mode
If the instrument is set in Hold mode, a new button will be shown on the
Communicate screen, just under the Run button. As with Single mode, data is
available for display in all screens, but update will occur every time the Get
Held Data button is pressed. The sequence of operation should therefore be
Run button, Get Held Data button, Run button, Get Held Data button, etc.
All Other Modes
Display screens will be updated automatically as data is received
All display screens will be available under separate tabs – to view data, simply click on the desired tab.
Refer to Chapter 7 for a description of each screen.
5.2 REAL TIME DATA
From the opening screen of DataLog 400, the user will have been
aware of a section titled “Real Time Data”. This section has two
functions – allowing the recording of real time data to disk as it is
received, and limiting the amount of data that will be displayed at any
one time.
5.2.1
REAL TIME DATA LOGGING
All data is received in real time in ASCII text format. This data may be
logged as a text file for subsequent viewing within DataLog 400, or for importing into another software
package.
To record real time data as it is received, simply click on the Real time Data Logging button:
A standard Windows type dialogue box will be shown, asking the user to enter a file name under which to
save the data. The default extension is *.txt. Once the user clicks on OK, all data received will be added
to this file, until the instrument is stopped.
Note that the software will allow existing files to be overwritten. However, the immediately previous
contents of any overwritten file will be stored as another text file titled *.bak.
5.2.2
SELECT MAX VIEWABLE DATA POINTS
This feature has been included to prevent the potentially large amounts of incoming data from adversely
affecting PC performance. As each line of data is received through the PC comm port, it is held in PC
RAM, and also added to the Scroll and Plot display pages (each of which also uses PC RAM). On the Plot
page particularly, some older, slower PC’s may struggle to cope with plotting these large amounts of data.
The Real Time Data feature therefore allows the user to set the maximum number of data lines that will be
viewable in the graphical display of DataLog 400. Once this limit is reached, the oldest data will be
removed, so that only the most recent data points are visible. To choose the required number of visible
data points, simply type into the text box, and click the Set button.
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5.2.3
Note that the number of lines of data in the Scroll screen is automatically set to 16360. Again, once full,
the oldest data will be removed.
AML EMULATION MODE
The MODUS SVS has an alternative operating mode, where it exactly emulates an Applied
Microsystems Ltd Smart Sensor. In this mode, the Modus SVS will only respond to AML type
commands, which are listed in Appendix 1.
To operate in this mode, enter the command #012;AML<cr>
Note: the instrument will now only respond to the AML codes listed on page 49.
To return to Valeport operating mode, the Modus SVS will respond to the command VALE<cr>
Note: the instrument will now only respond to the Valeport codes listed on page 48 & 49
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6
DATA VIEWING
DataLog 400 offers three different display modes. All are available for both real time data and for files that
have been saved.
6.1 OPENING STORED DATA FILES
Stored data files may be opened by clicking on this button in the
Communicate screen. The following dialogue box will appear,
asking the user to select which file to open. Note that only one file
may be opened at a time.
Files containing data that have been stored from a real time input will have the extension .txt, as described
in Chapter 5.2.1.
Once the desired file has been selected, click on
the Open button. As with viewing data in real
time, the user will be asked which parameter to
use as the x axis in graphical displays. Select the
required parameter, and click on OK.
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6.2 SIMPLE DISPLAY
The simple display is designed primarily for real time use. It is available for use with uploaded data files,
but will simply display each data point in turn as it is read from memory, and then fix on the final data
recorded in the file.
The function of the simple display is to provide the user with a readout of the last set of data received by
the PC.
The display gives the date and time of the last data point, and then the last output of each fitted parameter.
In Burst modes, the standard deviation of the data is also given.
Note the check box at the top right corner of the screen – while this is checked, the screen will continue to
be updated. Some older PCs may struggle to update all displays at fast data rates, so disabling unwanted
displays may help. To disable the display, simply uncheck the box. To re-enable, re-check the box – the
next data point received will be displayed as normal.
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6.3 SCROLL DISPLAY
The scroll display provides the user with a record of all data received by the software (subject to the
maximum number of lines, 16360).
The screen shows the date and time at the left-hand side, followed by data from each fitted parameter.
Again, if in Burst mode, standard deviation data will be included.
Note that the columns of data are sizeable, after the first two lines of data have been received. Simply
position the mouse over the edge of a column title, and use the left mouse button to drag the column to a
suitable size.
As with the Simple display, this screen can be disabling by unchecking the Enable check box at the top
right corner. Re-checking the box re-enables the display, and data will continue to be added when the
next data line is received.
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6.4 GRAPHICAL DISPLAY
The graphical display facility in DataLog 400 is an integral feature of the Delphi programming language in
which DataLog 400 is written. Consequently, there are many features of this display type that are beyond
what is absolutely necessary for functional data display. Such features include adding a picture to the
background of the graph, and changing the size of the border around the image.
This manual does not cover the majority of these features, but instead concentrates on those features that
are necessary to enable standard data displays. Users familiar with standard Windows functions and
common programmes such as Microsoft Excel will be able to customise their graphical displays as they
wish, simply by exploring the many features available.
When the user first views the graphical display, they will be presented with a blank page:
All graph functions are controlled with the various buttons at the top of the screen. The first
button to use is the Graph Edit button – this allows the user to decide which parameters are
to be graphed, and in which format. Clicking on this button reveals the following screen:
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All the fitted parameters are shown as being available for graphing against time. Simply click on the check
box against each parameter to indicate whether it is to be graphed or not.
To alter the colour of any parameter, simply double click on the coloured line adjacent to each parameter,
and select from the variety of available colours. Further modifications to line style can be made by
selecting the upper Series tab, followed by Format, and the Border button.
Finally, users may double click on the icon to the left of each parameter to alter the graph type. DataLog
400 is best able to display data at rapid rates using the “Fast Line” style, which is the default. However,
users may wish to select other styles to suit their own preference.
As can be seen from the screen on the previous page, there are several other tabs available to alter the
appearance of the graph. This manual does not cover all these options, but be assured that DataLog 400
will revert to its default style if closed down and reopened.
The example screen below shows only a single parameter checked for display, simply for reasons of
clarity. Note that secondary y axes will appear for each parameter checked, and each will autoscale to
show the full range of data. The scale may be manually set under the Chart, Axis, Scale tab. The x axis
will also autoscale as new data is received, and will then slide as the maximum number of viewable data
points is reached (Chapter 5.2.2).
Note that once the graph has been set up, the function buttons are inactivated and greyed out. This
inactivation is simply to conserve PC RAM for data display, and the buttons may be reactivated simply by
clicking on the toolbar.
The functions of the other buttons are as follows:
Clicking on this button will allow the user to print the graph. A preview page is shown, allowing the user
to alter page size, margin size and printer. Simply press Print when the page is shown as required.
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This button copies the graph as currently displayed to the PC clipboard, for import into other programs as a
bitmap.
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The remainder of the icons on the graphical display page allow the user
to control certain features of the graph using the mouse.
6.4.1
SCROLL & FOCUS
The first icon (default icon when the screen opens) gives the mouse two functions. By holding
down the right mouse button, it is possible to scroll both axes of the graph, simply by dragging the
mouse in the appropriate direction.
By holding down the left button, the
user may focus onto a particular section
of the graph. Simply drag and draw a
box over the required section of data,
starting at the top left corner.
To focus out again, drag and draw a
box on the graph starting at any other
corner.
The remaining icons alter the 3 dimensional properties of the graphical display.
If any are selected, the graph will automatically switch into 3D mode, but at
any time, 3D mode can be toggled on and off by using the 3D button.
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6.4.2
ROTATE
This icon allows the user to rotate the graph so that it may be viewed from any position either
above or to the right of the current perspective. Simply use the left mouse button to drag the
graph to the desired orientation.
6.4.3
MOVE
This icon allows the user to alter the position of the graph on the page. Use the left mouse button
to drag the graph around the page to the desired position. This picture shows the graph moved to
the left hand side of the screen.
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6.4.4
ZOOM
As can be guessed from the icon, this button allows the graph to be zoomed in or out. Holding
down the left mouse button, drag the mouse upwards to zoom in, or downwards to zoom out.
This picture shows the graph zoomed out:
6.4.5
DEPTH
This button controls the three dimensional depth of the graph. It is best seen in graphs that have
been rotated to view from a different perspective.
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7
CALCULATION
The Calculation function is provided as a tool for the user to carry out standard oceanographic
calculations.
Simply input Conductivity/Salinity, Pressure Temperature (in IPT68 or IPT 90 scales) and Latitude (if
known), and click on the Calculate button. The program will calculate and display the following
parameters:
•
Density Anomaly Gamma (difference between calculated Density and Density of Pure Water)
•
Conductivity or Salinity (whichever the user did not enter).
•
Sound Speed calculated using the chosen Speed of Sound
Formula.
•
Depth in metres calculated using the UNESCO standard formula. This is an approximation, and does
not account for variations in density distribution throughout the water column. Its accuracy has been
estimated at better than 0.1m.
All formulae, including the various Speed of Sound formulae are given in full in Chapter 10
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8
ABOUT
The About tab, available for selection at all times, shows Valeport’s contact details and software version. If
the About tab is selected after the user has interrupted the unit operation, then the instrument serial
number and internal firmware version will also be shown.
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9
CALCULATION FORMULAE
The following extracts are taken and adapted from "Processing of Oceanographic Station Data", published
by UNESCO in 1991.
9.1 SALINITY
The Practical Salinity Scale (PSS-78)
The fundamental step in constructing the practical salinity scale PSS-78 consisted of defining a single
reference point (S=35) on the scale as having the same electrical conductivity as a reference potassium
chloride (KCl) solution at 15°C and atmospheric pressure. The transition from the previous scale was
made by selecting a single batch (P79) of Standard Seawater and equating the new scale to the old through
the chlorinity relationship S = 1.80655 Cl for that particular batch. As the salinity on the practical scale is
defined to be conservative with respect to addition and removal of water, the entire salinity range is
accessible through precise weight dilution or evaporation without additional definitions. However, the
practical scale is defined in terms of conductivity ratio and not by its conservative properties. Thus the
second part of the definition was constructed by measuring the conductivity ratio to the KCl standard or an
equivalent secondary standard over the entire range of salinities (1 to 42) of samples prepared by
evaporation or dilution of batch P79 SSW and computing an empirical formula S = S(R15), where R15 is the
conductivity ratio 15°C and atmospheric pressure to the KCl standard. Thus salinities on the PSS-78 scale
are defined by conductivity ratios alone. Salinities determined by any other method would not necessarily
coincide with the PSS-78 scale and would have to be identified separately. Lewis and Perkin (1981) and
Mamayev (1986) discuss differences between PSS-78 and previous scales and provide algorithms and
tables to convert existing data to the new scale.
The algorithm for converting conductivity ratio to salinity is constructed in terms of the conductivity ratio R
defined as:
R = C(S, t, p)/C(35, 15, 0)
(1)
where C(S, t, p) is the electrical conductivity as a function of salinity S, temperature t and pressure p. The
ratio is factored into the functions:
R = rt(t).Rt(S, t).Rp(R, t, p)
(2)
where
rt(t) = C(35, t, 0)/C(35, 15, 0)
Rt(S, t) = C(S, t, 0)/C(35, t, 0)
Rp(R, t, p) = C(S, t, p)/C(S, t, 0)
Salinity is given by the function
5
∆t
[a
S=
n=0
n
+
1+ k ∆t
bn ] ⋅ Rtn/2
(3)
with coefficients
a0 =
a1 =
a2 =
a3 =
a4 =
a5 =
+0.0080
-0.1692
+25.3851
+14.0941
-7.0261
+2.7081
b0 =
b1 =
b2 =
b3 =
b4 =
b5 =
+0.0005
-0.0056
-0.0066
-0.0375
+0.0636
-0.0144
k=
∆t =
+0.0162
t - 15
At t = 15°C (3) reduces to the formula defining the practical salinity scale (Perkin and Lewis 1980).
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The factors rt and Rp are given by
4
Cn t n
rt =
(4)
0
where
C0 =
C1 =
C2 =
+0.6766097
+2.00564E-2
+1.104259E-4
C3 =
C4 =
-6.9698E-7
+1.0031E-9
and
Rp = 1 +
e1 p + e2 p 2 + e3 p 3
1 + d 1t + d 2 t 2 + ( d 3 + d 4 t ) ⋅ R
(5)
= 1+
C
B + AR
with
e1 =
e2 =
e3 =
+2.070E-5
-6.370E-10
+3.989E-15
d1 =
d2 =
d3 =
d4 =
+3.426E-2
+4.464E-4
+4.215E-1
-3.107E-3
for temperature in °C and pressure in dBar.
Given a measurement of R, t and p, salinity is computed by solving (2) for Rt; Rt = R/(rtRp) and evaluating S
from (3). If conductivity ratio R is required given S, t and p, the ratio Rt can be found by numerical
inversion of (2), and R can be found by solving the quadratic equation
R = rt ⋅ Rt ⋅ Rp = rt ⋅ Rt ⋅[1 +
C
AR + B
]
or
R=
[( Ar R − B )
t
t
2
+ 4 rt Rt A( B + C )]1/2 + [ Art Rt − B ]
2A
(6)
This description of PSS-78 has been adapted from Fofonoff (1985)
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9.2
DENSITY ANOMALY GAMMA
Equation of State of Seawater (EOS-80)
The equation of state of seawater is the mathematical expression to calculate density from measurements
of temperature, pressure and salinity. Virtually all the computations of density of seawater made since the
beginning of the century have been based on the direct measurements of density, chlorinity and salinity
made by Knudsen, Forch and Sörensen (1902), and of compression of seawater made by Ekman (1908).
This equation was obtained from measurements of density of natural seawater in which the proportions of
the various ions are not exactly constant. To be consistent with the new definition of the Practical Salinity,
1978, the new equation of state is based on measurements of density of standard seawater solutions
obtained by weight dilution with distilled water and by evaporation. As the absolute density of pure water
is not known with enough accuracy, the density of distilled water used for these measurements was
determined from the equation of the SMOW (Standard Mean Ocean Water) whose isotopic composition is
well defined.
The new equation of state (EOS-80) which was adopted by JPOTS in 1981 (UNESCO, 1981c) is:
v ( S , t , p ) = v ( S , t , 0)[1 − p / K ( S , t , p )]
3/ 2
ρ( S , t , 0) = 1 / v ( S , t , 0) = A + BS + CS + DS
3/2
2
3/ 2
K ( S , t , p ) = E + FS + GS + ( H + IS + JS ) p + ( M + NS ) p
2
}
(7)
where the coefficients A, B, .....N are polynomials in temperature t. Units: salinity, PSS-78; temperature,
°C; pressure (p), bar; density (ρ), kg/m3; specific volume (v), m3/kg. These coefficients are given below.
t0
t1
t2
t3
t4
t5
A
+999.842594
+6.793952E-2
-9.095290E-2
+1.001685E-4
-1.120083E-6
+6.536332E-9
B
+8.24493E-1
-4.0899E-3
+7.6438E-5
-8.2467E-7
+5.3875E-9
C
-5.72466E-3
+1.0227E-4
-1.6546E-6
t0
t1
t2
t3
t4
E
19652.21
+148.4206
-2.327105
+1.360477E-2
-5.155288E-5
F
+54.6746
-0.603459
+1.09987E-2
-6.1670E-5
G
+7.944E-2
+1.6483E-2
-5.3009E-4
t0
t1
t2
t3
H
+3.239908
+1.43713E-3
+1.16092E-4
-5.77905E-7
I
+2.2838E-3
-1.0981E-5
-1.6078E-6
J
+1.91075E-4
t0
t1
t2
M
+8.50935E-5
-6.12293E-6
+5.2787E-8
N
-9.9348E-7
+2.0816E-7
+9.1697E-10
D
+4.8314E-4
Density Anomaly γ is defined as the Density of the water minus 1000 kg/m3.
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9.3
SPEED OF SOUND
The following information, discussion and conclusions are taken from Special Publication No.34 of the
Hydrographic Society, prepared by JM Pike and FL Beiboer of METOCEAN plc. The report is entitled "A
Comparison Between Algorithms for the Speed of Sound in Seawater".
The following abbreviations and units are used:
V
T
S
φ
g(φ)
Pb
Pk
D
MODUS SVS Operating Manual
Computed speed of sound in seawater (m/s)
Temperature (°C)
Salinity
Latitude in degrees
Gravitational acceleration at the given latitude (m/s2)
Hydrostatic pressure (bar) (1bar = 105Pa = 10/g(φ) (kg/cm2)
Hydrostatic pressure (kg/cm2)
Depth (m)
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9.3.1
STANDARD FORMULAE
9.3.1.1
PRESSURE/DEPTH RELATIONSHIP
Several relationships are identified by Robertson(l), ranging from the approximate ("1 km of seawater
generates a pressure of 101 bar"), to the precise (use of the MacKenzie or UNESCO algorithms).
The accurate relationships require computation of the gravitational field at the latitude in question using an
appropriate formula for the gravitational field.
The UNESCO pressure/depth relationship has not been the subject of significant academic debate since its
introduction, and is stated as follows:
D=
( C1 * ( Pb * 10) + C2 * ( Pb * 10) 2 + C3 * ( Pb * 10) 3 C4 * ( Pb * 10 ) 4 )
+ ∆d / 9.8
( g ( φ ) + 12 g '* Pb )
where:
g(φ)
G'
C1
C2
C3
C4
Pb
∆d
= 9.780318 * (1.0 + 5.2788E-3 * sin2φ + 2.36E-5 * sin4φ+ )
= +2.184E-5 m.s-2. bar-1
= +9.72659
= -2.2S 12E-5
= +2.279E-10
= -1.82E-15, and
is the hydrostatic pressure (bar)
is the geopotential anomaly, expressed in J/kg. This term is zero for
standard seawater (S = 35, T = 0°C).
The geopotential anomaly term (∆d) contains the correction for the actual density distribution within the
water column, and can be evaluated for precise computation (or where there are extremes of temperature
or salinity) by integrating the specific volume anomaly over the required pressure range. The procedures
for this are also included in UNESCO Technical Paper #44.
The DataLog 400 program, however, does not feature the ability to input ∆d (which is therefore assumed
to be 0).
This assumption is recognised as being legitimate, with the resultant pressure depth algorithm called
'Simple UNESCO Depth':
D=
( C1 * ( Pb * 10) + C2 * ( Pb * 10 ) 2 + C3 * ( Pb * 10) 3 C4 * ( Pb * 10) 4 )
( g ( φ ) + 12 g '* Pb )
This value of D is used in all formulae within DataLog 400.
9.3.1.2
WOOD (1949)
V = 1410 + 4. 21 * T − 0. 037 * T 2 + 1.14 * S + 0. 018 * D
This formula was recognised before 1960 as being inadequate, and was replaced (at least in US Navy
Hydrographic Office operations) in 1962 by the Wilson formula. It is thus not used in DataLog 400.
MODUS SVS Operating Manual
Section 2, Page 40
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9.3.1.3
WILSON (OCTOBER 1960)
Full Version
The full version of this formula is:
V = 1449.14 + VT + VP + VS + VSTP , where
VT = 4.5721 * T − 4. 4532 E − 2 * T 2 − 2. 6045 E − 4 * T 3 + 7. 9851E − 6 * T 4
V P = 1. 60272 E − 1* Pk + 1. 0268 E − 5 * Pk2 + 3.5216 E − 9 * Pk3 − 3. 3603 E − 12 * Pk4
VS = 1. 39799 *( S − 35) + 1. 69202 E − 3 * ( S − 35) 2
VSTP = ( S − 35) *( −1.1244 E − 2 * T + 7. 7711E − 7 * T 2 + 7. 7016 E − 5 * Pk − 1. 2943 E − 7 * Pk2 + 3.1580 E − 8 * Pk * T + 1.5790 E − 9 * Pk * T 2 )
+ Pk *( −1.8607 E − 4 * T + 7. 4812 E − 6 * T 2 + 4.5283 E − 8 * T 3 )
+ Pk2 *( −2.529 E − 7 * T + 1.8563 E − 9 * T 2 )
+ Pk3 * ( −1. 9646 E − 10 * T )
Wilson states that the formula is valid to within ± 0.3 m/s in the ranges:
-4°C < T < 30°C; 0 < S < 37 1 kg/cm2; < Pk < 1000 kg/cm2.
where Pk = Pb ⋅
10
g ( φ)
Simplified Version
A simplified version of this formula, which is believed to have been used for a number of offshore surveys,
is:
V = 1. 449.14 + 4. 5721 * T − 4. 4532 E − 2 * T 2 − 2. 6045 E − 4 * T 3 + (1. 39799 − [1.1244 E − 2 * T ]) * ( S − 35) + 1. 643 E − 2 * D
The range of validity is likely to be comparable to the full version, with simplification (and inaccuracy)
introduced by replacing the pressure terms with a depth term (of unknown provenance), and ignoring 4th
order temperature terms (inter alia).
MODUS SVS Operating Manual
Section 2, Page 41
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9.3.1.4
MEDWIN (1975)
This simple formula was based on the Del Grosso equation and is:
V = 1449. 2 + 4. 6 * T − 0. 055 * T 2 + 0. 00029 * T 3 + (1. 34 − 0. 010 * T ) * ( S − 35) + 0. 016 * D
Medwin states the formula is valid "for realistic combinations of T, S, P" in the ranges 0 < T < 3S°C,
0 < S < 45, 0 < D < 1000 m. The fact that the equation was based on the Del Grosso equation, however,
leads to the conclusion that the range of validity cannot be superior to the Del Grosso formula itself, which
is deemed to be valid only in a limited temperature and salinity range.
The more likely validity of the Medwin formula is indicated in the matrix below, in which the maximum
valid pressure (in bar) is indicated for each temperature and salinity:
T (°C)
S
0
5
10
15
33
34
35
36
38
100
100
100
100
69
100
100
100
100
69
100
100
100
100
100
69
100
100
69
100
MODUS SVS Operating Manual
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9.3.1.5
CHEN AND MILLERO (1977)
This formula was adopted by UNESCO in 1983 and is as follows:
V = Cw ( t , p ) + A( t , p ). S + B( t , p ). S 3/ 2 + D( t , p ). S 2
where,
CW ( t , p ) = C00 + C01 . T + C02 . T 2 + C03 . T 3 + C04 . T 4 + C05 . T 5 +
( C10 + C11 . T + C12 . T 2 + C13 . T 3 + C14 . T 4 ). Pb +
( C20 + C21 . T + C22 . T 2 + C23 . T 3 + C24 . T 4 ). Pb2 +
( C30 + C31 . T + C32 . T 2 ). Pb3
A( t , p ) = A00 + A01 . T + A02 . T 2 + A03 . T 3 + A04 . T 4 +
( A10 + A11 . T + A12 . T 2 + A13 . T 3 + A14 . T 4 ). Pb +
( A20 + A21 . T + A22 . T 2 + A23 . T 3 ). Pb2 +
( A30 + A31 . T + A32 . T 2 ). Pb3
B ( t , p ) = B00 + B01 . T + ( B10 + B11 . T ). Pb
D ( t , p ) = D00 + D10 . Pb
with the coefficients defined in the following matrix:
Subscript
00
01
02
03
04
05
10
11
12
13
14
20
21
22
23
24
30
31
32
A
B
+1.389
-1.262E-2
+7.164E-5
+2.006E-6
-3.21E-8
-1.922E-2
-4.42E-5
+9.4742E-5
-1.2580E-5
-6.4885E-8
+1.0507E-8
-2.0122E-10
-3.9064E-7
+9.1041E-9
-1.6002E-10
+7.988E-12
+7.3637E-5
+1.7945E-7
+1.100E-10
+6.649E-12
-3.389E-13
C
+1402.388
+5.03711
-5.80852E-2
+3.3420E-4
-1.47800E-6
+3.1464E-9
+0.153563
+6.8982E-4
-8.1788E-6
+1.3621E-7
-6.1185E-10
+3.1260E-5
-1.7107E-6
+2.5974E-8
-2.5335E-10
+1.0405E-12
-9.7729E-9
+3.8504E-10
-2.3643E-12
D
+1.727E-3
-7.9836E-6
The Chen & Millero expression is based upon comprehensive observations on seawaters in the ranges
0<T<40°, 0<S<40, 0<Pb<1000. Some concern has been expressed, however, at the accuracy of the
formula at pressures exceeding 100 bar.
MODUS SVS Operating Manual
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9.3.1.6
DEL GROSSO (1974)
V = C000 + DCT + DCS + DC P + DCSTP , where
C000
= 1402. 392
DCT
= 0. 501109398873 E + 1 * T − 0. 550946843172 E − 1 * T 2 + 0. 221535969240 E − 3T 3
DCS
= 0.132952290781E + 1 * S + 0.128955756844 E − 3 * S 2
DC P
= 0.156059257041 * Pk + 0. 244998688441E − 4 Pk2 − 0.883392332513 E − 8 * Pk3
DCSTP
= −0.127562783426 E − 1 * T * S + 0. 635191613389 E − 2 * T * Pk
+ 0. 265484716608 E − 7 * T 2 * Pk2 − 0.159349479045 E − 5 * T * Pk2
+ 0.522116437235 E − 9 * T * Pk3 − 0.438031096213 E − 6 * T 3 * Pk
− 0.161674495909 E − 8 * S 2 * Pk2 + 0. 968403156410 E − 4 * T 2 * S
+ 0. 485639620015 E − 5 * T * S 2 * Pk − 0. 340597039004 E − 3 * T * S * Pk
The formula is deemed to be valid only in the temperature and salinity ranges, and up to the pressures
(bar), indicated in the matrix below:
T (°C)
S
0
5
10
15
33
34
35
36
38
1034
1034
1034
1034
69
1034
1034
1034
1034
69
275
207
414
275
414
69
207
207
69
414
MODUS SVS Operating Manual
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9.3.1.7
MACKENZIE (1981)
Based upon widespread oceanographic measurements, the MacKenzie formula is:
V = 1448. 96 + 4.591 * T − 5. 304 E − 2 * T 2 + 2 . 374 E − 4 * T 3
+ 1. 340 * ( S − 35) + 1. 630 E − 2 * D + 1. 675 E − 7 * D 2
− 1. 025 E − 2 * T * ( S − 35) − 7.139 E − 13 * T * D 3
and is stated to be valid for naturally occurring seawaters in the intervals indicated in the matrix below:
Pk
T (°C)
S
0
50
100
0-30
0-20
0-14
0-16
10-16
0-12
0-16
8-16
0-5
12-14
0-5
30-40
32-40
32-34
35-38
39-40
32-36
37
38-39
33-36
38-39
34-35
200
500
800
MODUS SVS Operating Manual
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9.3.2
DISCUSSION
9.3.2.1
DEVELOPMENT OF FORMULAE
A useful overview of the history of seawater speed of sound measurements and formulae is provided by
Dulshaw et al.
All formulae given above (and the majority of others referred to in the course of this study) were
empirically derived from measurements of acoustic velocity of seawater samples whose temperature,
salinity and pressure were measured in the oceans and/or varied in the laboratory. The Robertson equation
is one of the few attempts to base the equations for the speed of sound on theoretical considerations alone.
The Wood formula, while in use even now, was considered as early as 1960 to be unreliable for the
advancing technology and requirements of that era, and was superseded by the Wilson formula in 1961.
The recognition of defects in the experimental methods of Wilson, together with the adoption of the
practical salinity scale and the international equation of state for seawater (EOS-80) resulted in the Wilson
formula being superseded for oceanographic purposes by the Chen & Millero formula, which still
represents the formal standard for oceanographic purposes.
The limitations of the Chen & Millero formula in turn were revealed by precise in situ observations of
acoustic velocity with depth, and by the advent of tomographic methods to determine seawater physical
properties along very large path-lengths (across oceans) and to great depths.
These observations have led in recent years to the realisation that the Chen & Millero formula has distinct
limitations at high pressures, and that the Del Grosso equation may be more realistic for such specialist
purposes. The wide validity range for salinity and temperature of the Chen & Millero formula is of value for
measurements on the continental shelf, however. The quality of fit of the Del Grosso equation to the
modern high-pressure data sets (and the corrections that should consequently be applied to the Del Grosso
equation) is currently the subject of some debate.
9.3.2.2
COMPARISON OF FORMULAE
The Wood and Wilson formulae do not fit modem experimental and observational data well, and should
no longer be used for precise computations. This probably is the result of improvements in observational
and analytical techniques over the years, together with changes in computational methods of salinity and
depth.
The remaining algorithms show fairly close agreement with one another, diverging as pressure increases.
The Chen & Millero formula is commonly accepted for oceanographic use, and was derived from
measurements over a wide salinity, temperature and pressure range.
MODUS SVS Operating Manual
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At high pressures (>100 bar), however, recent research suggests that the Del Grosso equation is more
accurate, although this formula is valid only for a limited range of oceanic waters.
The Del Grosso formula has been used as a benchmark to appraise the accuracy of the other algorithms.
The following order of preference is suggested:
i)
ii)
iii)
iv)
Chen & Millero (only for water depths less than 1000m)
Del Grosso (only for water depths greater than 1000m)
MacKenzie (for rapid computations in oceanic waters to 8000m water depth)
Medwin (for rapid computations in oceanic waters to 1000m water depth)
The Medwin and Wilson (simplified) formulae diverge considerably from the remaining algorithms at
temperatures greater than 20°C. This is expected from two simple formulae lacking higher order
temperature terms.
There may be some advantages in using the MacKenzie and Medwin formulae where depth is known, and
where the computation of pressure for inclusion in the Chen & Millero or Del Grosso formulae would
become unnecessarily onerous. The user should be made aware, however, of the limited range of
conditions of temperature, salinity and pressure over which these formulae are valid.
9.3.2.3
THE PRESSURE/DEPTH ALGORITHM
An accurate expression for computing pressure from depth (and vice versa) may be desirable:
a)
for its own sake, to enable precise pressure and depth computations to be made for a variety of
purposes; and
b)
to enable precise speed of sound computations to be made.
When using speed of sound algorithms with a pressure term (Chen & Millero, Del Grosso), the water
pressure can be measured directly, estimated from a known depth and inversion of the UNESCO pressure/
depth algorithm (possibly based on a carefully calibrated conductivity/temperature/depth cast), or
calculated from standard tables. According to Saunders and Fofonoff, who were the originators of the basic
method adopted in the UNESCO formula, these estimates should be carried out at 5 bar pressure intervals
near the surface and at 200 bar intervals for greater depths.
When using speed of sound formulae with a depth term (MacKenzie or Medwin), the depth may be
estimated or measured by some independent means; or computed from a pressure measurement and a
conductivity/temperature depth cast. It is more likely, however, that these methods would not be used for
precise purposes; they are in any case valid only for oceanic waters in which the errors in the estimation of
depth, introduced through ignoring the geopotential anomaly, would not be excessive.
MODUS SVS Operating Manual
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9.3.3
CONCLUSIONS
1.
It is recommended that use of the Wood and Wilson formulae be discontinued for precise
purposes, as they do not provide good agreement with modern data sets and computational
methods of salinity and depth.
2.
It is of crucial importance to ensure that the formulae (of whatever origin) are used only for
observations made within the ranges of temperature, salinity and pressure for which each
expression is deemed valid.
3.
It is recommended that the Chen and Millero formula be used for seawaters on the continental
shelf. This incorporates a pressure term which should be measured directly; evaluated from a
known depth using the full UNESCO formula and data obtained either from oceanographic tables
or from a conductivity/temperature/depth cast; or the error in using the simplified UNESCO
formula deliberately accepted.
4.
In deep ocean waters, the Del Grosso formula is currently favoured, especially for long pathlengths. This also uses a pressure term.
5.
Where rapid computations are necessary, or where the depth is known (but not pressure), the
simple MacKenzie (9 terms) and Medwin (5 terms) formulations may prove of value. These
expressions are strictly valid only for normal oceanic waters. Where depth is computed from
pressure, the simplified UNESCO equation for the pressure/depth relationship could be used
without introducing significant error.
6.
Incorporation of the full UNESCO pressure/depth algorithm (incorporating the geopotential
anomaly) would be a useful addition to any software package, although there may be little
discernible benefit to the accuracy of the speed of sound computations. The complete formula
would, however, enable a full suite of precise applications to be available for use worldwide.
MODUS SVS Operating Manual
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10
APPENDIX 1
CONFIGURATION CODES
General control codes #000 - #099
Code
#000
Do Not Use
Followed By
Operation
Used as an error code
#001
;modus_address<CR>
Sets the modus address
#002
<CR>
Sends the modus address
#003
;mode;rate;period;interval;average;
moving_ave_length<CR>
Sets the sampling regime
#004
<CR>
Sends the sampling regime
#005
;ON<CR> or ;OFF<CR>
Turns ON or OFF address mode
#006
<CR>
Sends ON or OFF for address mode
#007
;RAW<CR> or ;CAL<CR>
Sets the output to be raw or calibrated values
#008
<CR>
Sends the output values raw or cal
#009
;TARE<CR>
Sets the tare value in systems with pressure fitted
(If no value entered a measured value is used)
Only if
pressure fitted
#010
<CR>
Sends the tare value
Only if
pressure fitted
#011
<CR>
Scans the I2C bus to see what devices are fitted
#012
;AML<CR>
Sets the unit to AML mode accepting only AML
commands
#013
;OUTPUT_MODE<CR>
Sets the output format used :AML,VALEPORT,CSV,SVP16,NMEA,
WESTGEO,SOUNDER,HYPACK,SEABIRD
#014
<CR>
Sends output format to be used
#015
<CR>
Sends last reading
#016
;ON<CR> or ;OFF<CR>
Turns on or off ident option
#017
<CR>
Sends ident option on or off
#018
;module_address;units;units<CR>
Sets valeport calibrated units label
#019
<CR>
Sends valeport calibrated units label
#020
;module_address;units;units<CR>
Sets user calibrated units label
( Space means no user cal to be used
@ means user cal to be used but no units)
MODUS SVS Operating Manual
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Not available
on SVP
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#021
<CR>
Sends user calibrated units label
#022
;
module_address;parameter_no(1or2);fi
t(15);coef5; coef4; coef3; coef2; coef1;
offset<CR>
Sets USER calibration in module module_address
parameter parameter_no to a fith order polynomial
defined by the coefficients.
#023
;module_address;parameter_no <CR>
Sends USER calibration in module module_address
parameter parameter_no
#024
;
module_address;parameter_no(1or2);fi
t(15);coef5; coef4; coef3; coef2; coef1;
offset<CR>
Sets VALEPORT calibration in module
module_address parameter parameter_no to a fifth
order polynomial defined by the coefficients.
#025
;module_address;parameter_no <CR>
Sends VALEPORT calibration in module
module_address parameter parameter_no
#026
;valeport_separator<CR>
Sets the valeport output string separator
#027
<CR>
Sends the valeport output string separator
#028
<CR>
Puts unit into run
#029
;pressure_trip;pressure_increment
<CR>
Sets the depth sampling parameters
Only if
Pressure fitted
#030
<CR>
Sends the depth sampling parameters
Only if
pressure fitted
#031
Continuously sends calibrated or raw data from
specific module as set by unit_address.
#032
;unit_address;RAW<CR>
or
;unit_address;CAL<CR>
<CR>
#033
;SERIAL_NUMBER<CR>
Sets the units serial number
#034
<CR>
Sends the units serial number
#035
;unit_address; parameter_no(1or2)
;gain;offset<CR>
Sets the gain and offset values for module
unit_address parameter parameter_no.
#036
;unit_address;
parameter_no(1or2)<CR>
Sends the gain and offset values for module
unit_address parameter parameter_no.
#037
;unit_address<CR>
Sends the module software version.
#038
;unit_address;AUTOorRESET<CR>
Performs SVP characterisation
#039
;unit_address;
parameter_no(1or2);gsr1;gsr2;tfr1
<CR>
;unit_address;
parameter_no(1or2)<CR>
Sets the gsr registers and tfr1 register in the module
selected for the parameter selected
#040
Sends the software version number.
SVP Only
Sends the gsr registers and tfr1 register in the module
selected for the parameter selected
AML COMMANDS
Code
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Operation
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R<CR>
Sets unit to operate in RAW data units
RE<CR>
Sets unit to operate in real or cal units
S<CR.
Performs single measurement
M<CR>
Performs multiple measurements forever (only cycling the power will restart the device)
VALE<CR>
Set to valeport command mode (AML commands are no longer accepted)
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