1. MAVS Current Measurement
Nobska Development, Inc.
Albert J. Williams 3rd
Archie Todd Morrison III

2. Current Measurements Mechanical Sensors Electro-Magnetic Sensors
Doppler Sensors
LDV
Acoustic Doppler
Acoustic Doppler Profiling
Acoustic Travel-Time Sensors

3. Mechanical and EM Sensors
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

4. Doppler Sensors LDV – Laser Doppler velocimeters
Narrow range of particle densities over which it has good signal, requires many realizations to obtain low velocity noise
Acoustic Doppler single point sensors
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

5. Doppler Sensors Acoustic Doppler profilers (ADCP)
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

6. Doppler Sensors Acoustic Doppler profilers (continued)
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

7. Acoustic Travel-Time Sensors
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

8. Acoustic Travel-Time Sensors
c + u
c - u L

9. Applications of Current Measurement, Requirements
Transport
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
Waves
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
High frequency sampling, typically 20 Hz
Fine spatial resolution, typically 1/3 of distance from the boundary

10. Current Meter Moorings and Rigid Supports
Mooring cage
Carry mooring tension around current sensor
Bottom Tripod
Sensor inside tripod or sticking up in cage, MAVS illustrated
In-line support
Near bottom with float, MAVS illustrated at Juan de Fuca hydrothermal vent
Piling
Rigid mount above bottom in shallow water

11. Nobska - MAVS3 Modular Acoustic Velocity Sensor 3rd Generation
"Standard" MAVS3
with CTD option
Nobska

12. Memory TT8 MAVS Flash (ROM) SCP RAM Run-time EEPROM Configuration
Deployment Definition
MAVS
Flash Card Data
Configuration

13. Net Relative Velocity, Tilt, Heading
COD END
DIRECTION OF TOW

14. MAVS Specifications Sensitivity and linearity
0.05 cm/s sensitivity, 0.5% linearity (corrected to that in 2003)

15. MAVS Specifications Velocity zero offset stability
0.5 cm/s per deployment, no net drift with time
Demonstrated sensitivity to pressure and temperature on deployment in gel to 2000 m

16. MAVS Specifications Cosine response
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°

17. MAVS Specifications Compass
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

18. MAVS Specifications Tilt 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

19. MAVS Specifications Toughness Fouling sensitivity
Carried by submarine landslide 550 m down Monterey Canyon. Still recording pressure although sensor rings sheared off and tube bent 90°.
Fouling sensitivity
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

20. MAVS Carried 550 m in Monterey Canyon Landslide and Buried Alive
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°

21. MAVS Operation Setup with PC and deck box: Menu mode
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

22. MAVS Operation Setup with PC and deck box: MAVSoft mode
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

23. MAVS Operation Set time: Menu mode Set time: MAVSoft Mode
When screen says “Change time & date?” type y <enter>
Type month_day_year_hour_minute_second <enter>
Set time: MAVSoft Mode
Push button “SET TIME”
Push button “Send PC Time to MAVS”

24. MAVS Operation Calibration: Menu mode, select Calibration
Select Velocity Offsets: V <enter>
Place sensor in still water
Type M, <enter>, <enter>
Accept if STDV values are less than 0.15 cm/s
Select Compass Offsets: C <enter>
Follow instructions
Select Tilt Offsets: T <enter>
Save constants and exit
Type x, <enter>

25. MAVS Operation Calibration: MAVSoft mode, select MavsTerm
Select Calibration: 3 <enter>
Select Velocity: V <enter>
Place sensor in still water
Type M, <enter>, <enter>
Accept if STDV values are less than 0.15 cm/s
Select Compass Offsets: C <enter>
Follow instructions
Select Tilt Offsets: T <enter>
Save constants and exit
Type x, <enter>

26. MAVS Operation Deploy: Menu mode, select Deploy
Frame, select MAVS, earth Cartesian, or earth speed and direction
Logging enabled as append or overwrite
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
There are opportunities to revise deployment parameters

27. MAVS Operation
Deploy: MAVSoft mode, from Control Panel select Parameters, press UPLOAD
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.

28. MAVS Operation Offload: Menu mode Offload: MAVSoft mode
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
Select Offload
Name file to which the data will be captured

29. MAVS Operations Flash Card Ops: Menu mode Control C to get control
2 <enter>
Note data files with selection 2
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.

30. MAVS Data Analysis MAVSPack Plot
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
Load into Excel
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
Generate m files for data manipulation and plotting

31. MAVS Deployment Choices
Low energy flow
Long deployments, infrequent samples
Wave “interference”
Average over wave or mooring motion, measurement frequency high enough to resolve motion
Wave spectra
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
Highest frequency to resolve turbulent eddies, burst to extend duration of deployment

32. Batteries for MAVS Basic alkaline Lithium Double lithium
4.8 ah at 12 volts
Lithium
9.6 ah at 12 volts
Double lithium
19.2 ah at 12 volts
Power consumption is reduced by allowing time between bursts so MAVS can go into low power sleep

33. Data Storage for MAVS Compact flash memory
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

34. Real Time MAVS RS232 output RS485 output Power source 100 foot limit
Half duplex, not supported by MAVSoft
More than 1000 feet possible
Power source
12 volt low impedance (must provide 2 amps for 15 ms each measurement)
24 volt with internal regulator, typically 60 ma

35. Ancillary Sensors for MAVS
Pressure
Omega or Druck, 20 meters to 6000 meters full scale range
External temperature
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
Aanderaa inductive head, range 0 to 75, resolution 0.02, and accuracy 0.2 mS/cm
Optical turbidity
OBS, LBSS, or SeaPoint
Analog voltage from external source

36. Analog Output MAVS Integration with existing data systems
Output voltage range +/- 5 v for +/- 180 cm/s
External strobe possible
Calibration signals provided

37. Other Specials for MAVS
Bent sensor
90° right or left bend of sensor from body
90° up or down bend from body
Inverted sensor, vertical up or down
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

38. Setup Menu for MAVS
Configuration parameters may be changed in the setup menu, accessible with a password to prevent accidental entries
S <enter> WHIPR <enter> gives entry
Orientation can be selected
Ancillary sensors can be disabled or enabled
X <enter> stores new configuration

39. Downloading New Versions of MAVS Firmware
Enter TOM8 monitor
Type q <enter> nobska <enter>
Change communications setup for a baud rate of 9600
Download and open new distribution software, MAVSxy_z.zip
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