mavs current measurement
TRANSCRIPT
MAVS Current Measurement
Nobska Development, Inc.Albert J. Williams 3rd
Archie Todd Morrison III
Current Measurements
Mechanical Sensors Electro-Magnetic Sensors Doppler Sensors
LDV Acoustic Doppler Acoustic Doppler Profiling
Acoustic Travel-Time Sensors
Mechanical and EM Sensors
Mechanical 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 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
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
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
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
Acoustic Travel-Time Sensors
uc
LtLR +
=uc
LtRL −
=
u
c + u c - u
L
tcu
c
Lu
uc
Lut
2
22 2
222
∆⋅=⇒≈−
=∆
L
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
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
Nobska - MAVS3Modular Acoustic Velocity Sensor
3rd Generation
"Standard" MAVS3 with CTD option
Nobska
Memory
TT8 Flash (ROM) SCP RAM Run-time EEPROM Configuration
Deployment Definition MAVS
Flash Card DataConfigurationDeployment Definition
Net Relative Velocity, Tilt, Heading
HEADING
DIRECTION OF TOW
COD END
MAVS Specifications Sensitivity and linearity
0.05 cm/s sensitivity, 0.5% linearity (corrected to that in 2003)
-20 0 20 40 60 80 100 120 140 160-50
0
50
100
150
200MAVS3 10104 Red - original transistors, Green - 2N2369A, Blue - 2N2369A without capacitors
Delay [ns]
Velo
city
readin
g [
cm/s
]
-20 0 20 40 60 80 100 120 140 160 180-2
-1
0
1
2
3
Velcity reading [cm/s]
Velo
city
err
or
[cm
/s]
-20 0 20 40 60 80 100 120 140 160 180-30
-20
-10
0
10
20
Velcity reading [cm/s]
Err
or
[%]
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
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1Filtered Velocity, Averaging Length: 100
Record Number
cm/s
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°
Vertical Cosine Response
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
-90 -70 -50 -30 -10 10 30 50 70 90
Elevation Angle
Co
rre
cte
d s
pe
ed
re
ad
ing
/to
w s
pe
ed
-30%
-25%
-20%
-15%
-10%
-5%
0%
5%
10%
15%
Pe
rce
nt
err
or
Scale Error
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
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
Tilt vs Pitch Reading
0
10
20
30
40
50
60
0.0 10.0 20.0 30.0 40.0 50.0 60.0
Tilt degrees
Pit
ch
de
gre
es
Pitch
Tilt1005 Inverted, Corrected
-1
-0.5
0
0.5
1
1.5
2
5 15 25 35 45
Celsius
De
gre
es
of
tilt
PitchRoll
MAVS Specifications Toughness
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
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°
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
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
MAVS Operation
Set time: Menu 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”
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> Follow instructions
Save constants and exit Type x, <enter>
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> Follow instructions
Save constants and exit Type x, <enter>
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
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.
MAVS Operation Offload: Menu 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
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.
MAVS Data Analysis MAVSPack
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
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
Batteries for MAVS Basic alkaline
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
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
Real Time MAVS RS232 output
100 foot limit RS485 output
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
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
Analog Output MAVS
Integration with existing data systems Output voltage range +/- 5 v for +/- 180
cm/s External strobe possible Calibration signals provided
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
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
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