MAVS Current Measurement
Nobska Development, Inc.
Albert J. Williams 3rd
Archie Todd Morrison III
Current Measurements
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Mechanical Sensors
Electro-Magnetic Sensors
Doppler Sensors
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LDV
Acoustic Doppler
Acoustic Doppler Profiling
Acoustic Travel-Time Sensors
Mechanical and EM Sensors
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Mechanical
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Rotor, vane – operate at very low power but have
poor response in low flows and in oscillatory
motion
Fan type – operate at low power, have good
response in oscillatory flow but exhibit dead band
in low flows
Electro-Magnetic

2-D, no dead band but response is poor to
accelerating flow, far field of electric field makes
calibration awkward in a tow tank
Doppler Sensors
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LDV – Laser Doppler velocimeters
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Narrow range of particle densities over which it has good
signal, requires many realizations to obtain low velocity
noise
Acoustic Doppler single point sensors
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df=(f1-f0)=2f0(u/c)cos(a), where a is the angle between the
acoustic beam and the current
ADV sensor is bistatic and measures velocity components at
a point. There are three acoustic paths
Acoustic Doppler current sensors suffer from weak returns if
there are few scatterers and may lock onto spurious returns
from supporting structures with zero velocity. Scattering
volume is remote from sensor head and fairly large
Doppler Sensors
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Acoustic Doppler profilers (ADCP)
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An entire profile of velocity is obtained
Monostatic, three or four acoustic axes diverge
from transducer head
Pulse burst must decay before next burst is
transmitted
Range depends on frequency, 300kHz gives about
150 meters range with good scatterers
Individual burst has large ambiguity in velocity,
many pings must be averaged to obtain speed
resolution desired
Doppler Sensors
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Acoustic Doppler profilers (continued)
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Velocity resolution*repetition rate = constant for
any particular frequency
Range*velocity resolution*repetition rate =
constant allowing frequency to be selected for
desired range. This tradeoff limits use of ADP for
turbulence measurements as well as large
ensonified volume
Broadband encoded bursts in BBADCP permit
effectively more pulses at once and this constant
is increased proportionally
Acoustic Travel-Time Sensors
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Defined acoustic path along which fluid
velocities are averaged
Depends only on the ability of the fluid
to transmit sound, no penalty for
moderate attenuation or for perfect
clarity
Linear velocity response through zero
velocity
Acoustic Travel-Time Sensors
u
c+u
c-u
L
t LR 
L
cu
2 Lu
2 Lu
t  2
 2
2
c u
c
t RL 

L
cu
c 2  t
u
2L
Applications of Current
Measurement, Requirements
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Transport
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Waves
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Average over waves and mooring motions, typically 20 seconds
Long deployment duration, typically 3 to 12 months
Excellent directional resolution and low velocity threshold, linearity
over large range in velocities
Bursts of duration capable of resolving spectrum at modest
sampling rate, typically 20 minutes at 2 Hz
Burst interval related to wave development, typically 2 hours
Boundary layer turbulence
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High frequency sampling, typically 20 Hz
Fine spatial resolution, typically 1/3 of distance from the boundary
Current Meter Moorings and Rigid
Supports
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Mooring cage
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Bottom Tripod
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Sensor inside tripod or
sticking up in cage, MAVS
illustrated
In-line support
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Carry mooring tension
around current sensor
Near bottom with float,
MAVS illustrated at Juan de
Fuca hydrothermal vent
Piling
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Rigid mount above bottom
in shallow water
Nobska - MAVS3
Modular Acoustic Velocity Sensor
3rd Generation
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"Standard" MAVS3
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with CTD option
Nobska
Memory
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TT8
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Flash (ROM)
RAM
EEPROM
SCP
Run-time
Configuration
Deployment Definition
MAVS
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Flash Card
Data
Configuration
Deployment Definition
Net Relative Velocity, Tilt,
Heading
HEADING
COD END
DIRECTION
OF TOW
MAVS Specifications
Sensitivity and linearity
0.05 cm/s sensitivity, 0.5% linearity (corrected to that in 2003)
Velocity reading [cm/s]
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MAVS3 10104 Red - original transistors, Green - 2N2369A, Blue - 2N2369A without capacitors
200
150
100
50
0
-50
-20
0
20
40
60
80
100
120
140
160
Velocity error [cm/s]
Delay [ns]
3
2
1
0
-1
-2
-20
0
20
40
60
80
100
120
140
160
180
120
140
160
180
Velcity reading [cm/s]
20
Error [%]

10
0
-10
-20
-30
-20
0
20
40
60
80
100
Velcity reading [cm/s]
MAVS Specifications
Velocity zero offset
stability
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0.5 cm/s per
deployment, no net
drift with time
Demonstrated
sensitivity to
pressure and
temperature on
deployment in gel to
2000 m
Filtered Velocity, Averaging Length: 100
1
0.8
0.6
0.4
0.2
cm/s

0
-0.2
-0.4
-0.6
-0.8
-1
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Record Number
MAVS Specifications
Vertical Cosine Response
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Horizontal cosine
response within
5% through 360°
Vertical cosine
response within
10% to 30° and
within 20% to 45°
On-axis response
is 20% low but
turbulence is
minimum
Tow tank shows
test run with
sensor at +45°
Scale
Error
1.05
15%
1.00
10%
0.95
5%
0.90
0%
0.85
-5%
0.80
-10%
0.75
-15%
0.70
-20%
0.65
-25%
0.60
-30%
-90
-70
-50
-30
-10
10
Elevation Angle
30
50
70
90
Percent error
Cosine response
Corrected speed reading/tow speed
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MAVS Specifications
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Compass
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Three magneto inductive
axes in orthogonal array
Tilt measured with two
axis solid state
accelerometer for
resolution of earth
magnetic field onto
horizontal plane
Second socket for
remounting of tilt sensor
for horizontal deployment
of MAVS
MAVS Specifications
Tilt
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Linearity within 1°
out to 50°
Temperature
compensated to 0.3°
of tilt between 5°C
and 45°C
Works equally well
inverted or on 90°
bracket for
horizontal mounting
50
Pitch degrees

60
40
30
Pitch
20
10
0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
Tilt degrees
Tilt1005 Inverted, Corrected
2
1.5
Degrees of tilt
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Tilt vs Pitch Reading
1
Pitch
Roll
0.5
0
-0.5
-1
5
15
25
Celsius
35
45
MAVS Specifications
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Toughness
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Carried by submarine
landslide 550 m down
Monterey Canyon. Still
recording pressure although
sensor rings sheared off and
tube bent 90°.
Fouling sensitivity
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Stops measuring only when
flow is totally blocked as in
illustration
Insensitive to particles,
bubbles, or perfectly clear
water. Only hard
obstruction or swim bladder
stops acoustic signal
MAVS Carried 550 m in Monterey
Canyon Landslide and Buried Alive
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MAVS on MBARI Frame with Homer acoustic beacon
ROV manipulated sand lifter exhuming frame
Upper portion of MAVS exposed
MAVS on deck, sensor stripped of rings and bent 90°
MAVS Operation
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Setup with PC and deck box: Menu mode
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Run a terminal emulator: Crosscut, Hyperterm,
TTOOLS, Kermit, etc.
Connect through the endcap to the deck box,
which provides power and a DB9 connector for
the PC’s RS232 serial comport
Configure the comport for 38,400 baud, 8 bits,
no parity
Turn on power and type Control C
MAVS Operation
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Setup with PC and deck box: MAVSoft
mode
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Bring up MAVSoft on the PC
Connect through the endcap to the deck
box, which provides power and a DB9
connector for the PC’s RS232 serial
comport
Turn on power
MAVS Operation
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Set time: Menu mode
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When screen says “Change time & date?”
type y <enter>
Type
month_day_year_hour_minute_second
<enter>
Set time: MAVSoft Mode
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Push button “SET TIME”
Push button “Send PC Time to MAVS”
MAVS Operation
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Calibration: Menu mode, select Calibration
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Select Velocity Offsets: V <enter>
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Select Compass Offsets: C <enter>
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Follow instructions
Select Tilt Offsets: T <enter>
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Place sensor in still water
Type M, <enter>, <enter>
Accept if STDV values are less than 0.15 cm/s
Follow instructions
Save constants and exit
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Type x, <enter>
MAVS Operation
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Calibration: MAVSoft mode, select MavsTerm
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Select Calibration: 3 <enter>
Select Velocity: V <enter>
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Select Compass Offsets: C <enter>
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Follow instructions
Select Tilt Offsets: T <enter>
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Place sensor in still water
Type M, <enter>, <enter>
Accept if STDV values are less than 0.15 cm/s
Follow instructions
Save constants and exit
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Type x, <enter>
MAVS Operation
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Deploy: Menu mode, select Deploy
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Frame, select MAVS, earth Cartesian, or earth speed and
direction
Logging enabled as append or overwrite
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Beware of overwriting data before reading it but beware of
starting with a partially filled compact flash
Measurement frequency, number of measurements per
sample
Samples per burst, burst interval
Delayed start (Start Time), duration of deployment
G <enter> to get analysis of battery and data storage
duration
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There are opportunities to revise deployment parameters
MAVS Operation
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Deploy: MAVSoft mode, from Control Panel select
Parameters, press UPLOAD
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Select frame (MAVS, earth Cartesian, or earth speed and
direction)
Enter measurement rate, number of measurements per
sample, samples per burst
Set burst interval and bursts per file
Establish the deployment schedule
Select Enable Logging to Flash Card and check append or
uncheck for overwrite
Press DOWNLOAD to put these parameters into MAVS
In Control Panel push DEPLOY
As data appear, select START LOGGING and name file for
capturing data on the screen.
MAVS Operation
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Offload: Menu mode
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Control C to get control (may need to do this three
times if MAVS is in a Low Power Sleep)
7 <enter>
Capture conversation with terminal (alt z in
Crosscut)
Offload: MAVSoft mode
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Select Offload
Name file to which the data will be captured
MAVS Operations
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Flash Card Ops: Menu mode
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Control C to get control
2 <enter>
Note data files with selection 2
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Data files contain data
Config.bin, Deploy.bin, and f_count.bin are required for
unpacking data
Select 4 <enter>, open MAVS case, and remove
compact flash card
Copy card contents to PC with Microsoft copy
command. Then return compact flash to MAVS
and type <enter> again.
MAVS Data Analysis
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MAVSPack
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Run MAVSPack selecting the folder into which the contents
of the compact flash were copied. This converts from binary
files to ASCII data files and ASCII configuration and deploy
files.
Plot
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Load into Excel
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Select columns for time, u, v, w and other ancillary parameters.
Time may be generated from hours, minutes, and seconds as
fractional hours
Select plot as scatter plot
Or load into Matlab
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Generate m files for data manipulation and plotting
MAVS Deployment Choices
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Low energy flow
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Wave “interference”
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Average over wave or mooring motion, measurement frequency
high enough to resolve motion
Wave spectra
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Long deployments, infrequent samples
Measurement frequency high enough to resolve highest frequency
wave
Burst long enough to resolve wave bands
Burst interval short enough to resolve change in wave climate
Turbulence
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Highest frequency to resolve turbulent eddies, burst to extend
duration of deployment
Batteries for MAVS
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Basic alkaline
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Lithium
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9.6 ah at 12 volts
Double lithium
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4.8 ah at 12 volts
19.2 ah at 12 volts
Power consumption is reduced by allowing
time between bursts so MAVS can go into low
power sleep
Data Storage for MAVS
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Compact flash memory
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16 MByte CF
64 MByte CF
256 MByte CF
Other capacities available to 1 GByte or
more
Industrial rating required for
temperature range of application
Real Time MAVS
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RS232 output
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RS485 output
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100 foot limit
Half duplex, not supported by MAVSoft
More than 1000 feet possible
Power source
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12 volt low impedance (must provide 2 amps for
15 ms each measurement)
24 volt with internal regulator, typically 60 ma
Ancillary Sensors for MAVS
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Pressure
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External temperature
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Aanderaa inductive head, range 0 to 75, resolution 0.02, and
accuracy 0.2 mS/cm
Optical turbidity
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Precision of 0.03°C and accuracy of 0.1°C
Internal temperature standard with precision of 0.03°C and
accuracy of 0.5°C
Conductivity
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Omega or Druck, 20 meters to 6000 meters full scale range
OBS, LBSS, or SeaPoint
Analog voltage from external source
Analog Output MAVS
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Integration with existing data systems
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Output voltage range +/- 5 v for +/- 180
cm/s
External strobe possible
Calibration signals provided
Other Specials for MAVS
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Bent sensor
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Inverted sensor, vertical up or down
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90° right or left bend of sensor from body
90° up or down bend from body
With solid state compass and tilt meter, this is
standard, selectable by user from the setup menu
Horizontal sensor

Internal tilt sensor must be moved from vertical
socket to horizontal socket and the change
entered in the setup menu
Setup Menu for MAVS
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Configuration parameters may be
changed in the setup menu, accessible
with a password to prevent accidental
entries
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S <enter> WHIPR <enter> gives entry
Orientation can be selected
Ancillary sensors can be disabled or
enabled
X <enter> stores new configuration
Downloading New Versions of
MAVS Firmware

Enter TOM8 monitor

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Type q <enter> nobska <enter>
Change communications setup for a baud rate of 9600
Download and open new distribution software, MAVSxy_z.zip
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MPREPxyz.rhx and MAVSxy_z.ahx is the new software release to
load to MAVS
In Crosscut select Tattletale, Load S-record, and MPREPxyz.rhx
Type G, select previous version from the menu
Next load MAVSxyz.ahx
Accept the burn to flash memory
Type G
Change baud rate back to 38,400