Vibrations Sensors: History, Signal Output and Calibration with Rockland Instruments

In 2010, 2-axis piezo-accelerometers (vibration sensors) and a precision inclinometer accurate to 0.1 degrees replaced three DC-response accelerometers in Rockland instruments. The new system produces far better low-frequency angle measurements and a much improved signal-to-noise ratio for higher frequencies. The purpose of the vibration sensors is not to quantify the acceleration of a VMP or MicroRider, but rather to produce a signal that is linear with respect to acceleration so that acceleration-coherent noise can be removed from the environmental signals measured by the shear probe.

The vibration sensors are piezo-ceramic beams that are anchored at one end and have a free cantilevered section over about one-half of their length. We glue a small weight near the tip in order to increase their sensitivity to vibrations. The signals from the beams are treated just like the signal from a shear probe. Thus, the sampled signal is proportional to the rate of change of acceleration and not to acceleration itself.

Rockland does not calibrate the sensors. Their sensitivity can vary by a factor of ~3.

Initially, we used the “type = accel” in the setup.cfg-configuration file to identify the piezo-vibration sensors. However, this is the same type that was used for DC-response accelerometers. This “type” requires two coefficients (coef0 and coef1) to convert the data into physical units. The piezo-accelerometers are not calibrated, so we used coefficients of “coef0=0″ and “coef1=1″, but this is not satisfactory because the second calibration coefficients has units of gravity and, consequently, the raw data are multiplied by a factor of 9.81.

Thus, we added a new signal type, namely “type = piezo”, to the identify the piezo-accelerometers  It does not need any coefficient, but will accept an offset coefficient “coef0 = offset_value”, if available. The main reason for adding this new signal type is to keep the spectra of vibrations on the same scale as the spectra of shear. Many of the plotting functions in the ODAS Matlab Library can detect that the acceleration signals come from piezo-accelerometers and will adjust the scaling of piezo-accelerometer spectra so that they remain visible in a figure of spectra from mixed signals. We thus strongly recommend that you used “type = piezo” in your configuration file. If you use “type = accel” AND use coefficients of 0 and 1, then these functions will assume that the signal comes from a piezo-accelerometer and not from a DC-response accelerometer, for backward compatibility.

The piezo-accelerometrers are inherently AC sensors with a low-frequency cut-off at 0.1 Hz. In addition, we do not know the frequency response of the vibration sensors but estimate that it must be at least to1000 Hz based on the elastic and dimensional properties of the ceramic and the mass that is attached to its tip.

When referring to the the two vibration sensors in a Rockland instrument, we use the nomenclature Ax and Ay because these implied co-ordinates correspond to those of a vertical profiler. If you are using the MicroRider on a glider or an AUV, then the co-ordinates are rotated by 90 degrees around the y-axis. For example, Ax becomes Az, and Ay remains Ay.

Two vibration sensors (Ax and Ay) embedded in front bulkhead block in the nose of the VMP-250 instrument. Signals from Ax and Ay are logged on the ASTP electronics board.

Rockland Customers Tow-Yow-ing the VMP-250

Rockland Scientific instrument users continue to push the operational boundaries of microstructure turbulence measurements.  A sub-section off these microstructure data collection trailblazers have been developing “tow-yow-ing” techniques with the VMP-250 to gather underway profiles in the mixed layer.

1. Oregon State University

Dr. Kipp Shearman, Dr. Johnathan Nash and the Ocean Mixing Group at OSU worked-up a “Tuna Reel” system for tow-yow-ing the VMP-250 to improve the spatial resolution of mixed layer profiles.  This system features the VMP-250 instrument with a Shimano electric fishing reel and a spectra line.  This rig has performed literally thousands of casts and it most recently returned a heavily operated campaign in the Alaska panhandle.

Kipp Shearman operating the OSU Shimano “Tuna Reel” rig for the VMP-250.


2. Tokyo University of Marine Science

In late 2016, Dr. Takeyoshi Nagai tested his idea for an “Underway-VMP”,  using his VMP-250 with the Teledyne Oceanscience Underway CTD winch and standard 1.5mm line.  Preliminary reports show that the system provided good data over two 15-hour tow-yo periods.  Fall speeds of the VMP-250 instrument and single long-brush are approximately 0.76 m/s on average with a “very steady [descent] speed”.  With a slow (i.e. 1-to-2 knots) ship speed, Takeyoshi completed a transect of 300m depth profiles with a 700 – 900m lateral resolution.








Check out more of the exciting research from Prof. Nagai at


3. University of Minnesota Duluth

Dr. Sam Kelly, who purchased a VMP-250 in early 2017, was intrigued by by OSU’s “Tuna-Reel” rig and the original Peter Gaube “ChUMP” CTD profiling system at the University of Washington Applied Physics Laboratory.  Sam purchased a Lindgren-Pitman S1200 Commercial Electric Reel with a wishbone rod, spectra line and a Optima Blue Top marine battery & charger.  The line is 600 lb braided hollow-core spectra from Lindgren-Pitman, it came pre-spooled.

Basically, there is a chunch of 2,000 lb spectra tied to the instrument and a stainless steel anchor swivel (just outside the tail). The swivel is then attached to the 600 lb line. The 600 lb line is spliced into an end loop (which was tested by UMD and was found to exceed to exceed a 680 lb breaking strength).

The VMP-250 and Lindgren-Pitman rig has been run continuously on 14 day campaigns on Lake Superior.  Each campaign results in roughly 10,000 casts to 50 m.

Two University of Minnesota Duluth students, Taeho Lim (left) and Kaelan Weiss (right), holding the VMP on the back-deck of the R/V Blue Heron in Lake Superior. Dr. Sam Kelly is grabbing a tool in front of them.

A Method for Determining Mixing Rates from Concurrent Temperature & Velocity Measurements

Ocean mixing has historically been estimated using Osborn’s model by measuring the rate of dissipation of turbulent kinetic energy and the background density stratification N while assuming a value of the flux Richardson number, Rif. A constant Rif of 0.17 is typically assumed, despite mounting field, laboratory, and modeling evidence that Rif varies.
This challenge can be overcome by estimating the turbulent diffusivity of heat K_T using the Osborn–Cox model. This model, however, requires measuring the rate of dissipation of thermal variance (chi), which has historically been challenging, particularly in energetic, flows because the high wavenumbers of the temperature gradient spectrum are unresolved due to the limitations of the current technology, i.e. the FP07 sensor:
    • The FP07 temperature signal is attenuated by the sensor and hence getting a true estimate of the signal variance is hard. This attenuation is poorly known and varies from unit to unit (FP07s are made by hand).  Rockland’s quick_look returns the spectrum of the gradient of temperature but this spectrum is not corrected for the response of the FP07 thermistor because there is no consensus on its frequency response.
    • The measured signal depends on the time constant of the FP07 thermistor — the scientific community is still unsure of its value and whether or not the response is single-pole or double-pole.
    • The time constant is speed-dependent because the properties of the boundary layer around the probe (e.g. thickness) are dependent on profiling speed.
    • Integrating the spectrum, without a correction for the response of the FP07, will under estimate the variance of the gradient of temperature and, hence, chi.

Therefore, the probe-dependent attenuation makes it hard to quantity the errors and the uncertainty involved with measuring high-wavenumber temperature gradient spectra.

To overcome this difficulty, a method in the paper Bluteau et al. 2017, Determining Mixing Rates from Concurrent Temperature and Velocity Measurements, is described that determines chi by spectral fitting to the inertial-convective (IC) subrange of the temperature gradient spectra.

While this concept has been exploited for moored time series, particularly near the bottom boundary, it can be used with data collected with gliders, and autonomous and ship-based vertical profilers, from which there are the most measurements.  By using the IC subrange, chi, and hence K_T, can be estimated even in very energetic events.  During less energetic periods, the temperature gradient spectra can also be integrated to obtain chi. In this paper, both of these techniques are used and analyzed for microstructure profiles collected at a site known for its very energetic internal waves. This study demonstrates that the spectral fitting approach resolves intense mixing events with K_T ≥ 10^-2 m2/s.

The validation of this method for microstructure profiling applications will allow Rockland instrument users to utilize their temperature measurements, in conjunction with velocity shear measurements, to calculate mixing rates with reduced error and uncertainty

To overcome this difficulty, a method in the paper Bluteau et al. 2017, Determining Mixing Rates from Concurrent Temperature and Velocity Measurements, is described that determines chi by spectral fitting to the inertial-convective (IC) subrange of the temperature gradient spectra.

While this concept has been exploited for moored time series, particularly near the bottom boundary, it can be used with data collected with gliders, and autonomous and ship-based vertical profilers, from which there are the most measurements.  By using the IC subrange, chi, and hence K_T, can be estimated even in very energetic events.  During less energetic periods, the temperature gradient spectra can also be integrated to obtain chi. In this paper, both of these techniques are used and analyzed for microstructure profiles collected at a site known for its very energetic internal waves. This study demonstrates that the spectral fitting approach resolves intense mixing events with K_T ≥ 10^-2 m2/s.

The validation of this method for microstructure profiling applications will allow Rockland instrument users to utilize their temperature measurements, in conjunction with velocity shear measurements, to calculate mixing rates with reduced error and uncertainty.

The full paper can be found here

UWA Researchers VMP profiling off the coast of Broome, Australia during the Kimberley Internal Soliton Sediment and Mixing Experiment.

Corrosion Prevention: Anodes, Nail-polish, and Continuity Checks

Extreme corrosion on a MicroRider-1000 after a long-term deployment with zinc anodes

Corrosion prevention is an easy to overlook, yet critical practice for operating in the corrosive environment of the ocean. Your Rockland Scientific MicroStructure instrument is equipped with one or more sacrificial anodes to prevent corrosion of your instrument. The anodes are electrically connected to the entire instrument providing protection to the instrument when submerged in seawater.

It is important to note that anode protection only works while the instrument is submerged in seawater.  When the instrument is in air, the anodes stop working and any residual sea water will cause corrosion to occur at vulnerable sites.  For this reason, it is important to thoroughly rinse the instrument with fresh water, especially when it is not active for more than 24 hours.  Before storing the instrument, it is imperative that the instrument is completely dried, as even fresh water (or dampness) can lead to corrosion if left long enough.

Zinc Anode vs. Aluminum Anode

Corrosion study with a MicroRider-1000

In 2015 Rockland Scientific’s Production Tech John Wells conducted an internal study of corrosion affecting RSI MicroStructure instruments. The key findings of the study are:

  • Aluminum anodes (mil spec. MIL-A-24779) provide superior protection and longevity than zinc anodes
  • Over time zinc anodes build a layer of oxidation that can insulate the anode from seawater diminishing its effectiveness
  • Aluminum anodes are formulated to slough off any oxidation resulting in continued peak performance. 
  • Placing a rubber washer under the anode helps prevent seawater from oxidizing the threads of the anode screw, thereby ensuring a good electrical connection. 

The study findings greatly enhanced the understanding of corrosion prevention at Rockland Scientific. If you have an instrument with an original zinc anode please ensure that the zinc is well scraped off before each deployment. Not all aluminum anodes are created equal, the study determined that a particular anode alloy formulation works best. RSI recommends that customers source their own spare aluminum anodes with mil spec: MIL-A-24779.  If you would like an aluminum anode to replace a zinc anode on your instrument please contact technical support to request a complimentary aluminum anode and rubber washer.   

Copper tab connecting the rear bulkhead to pressure tube

Consider the anode on the rear bulkhead of a VMP-250. The anode is electrically connected to the rear bulkhead by the threads of its mounting screw. The copper tab on the rear bulkhead contacts the inside of the pressure tube where the anodized layer has been intentionally removed. It is important to check that the copper tab is making a connection to the pressure tube. Overtime the copper tab can become bent and oxidized. The oxidization can easily be removed with sandpaper. You should hear and feel the tab making contact with the tube when the rear bulkhead is inserted into the tube. If you do not hear and feel the tab making contact then gently bend it back into place. You can test if the copper tab is effective by performing the continuity check described below.


Continuity Check

Checking the continuity between the rear bulkhead anode and a scratch on the pressure tube of a MicroRider-1000

Before you deploy your instrument, you can confirm the anode will do it job by performing a continuity check. Use a digital multimeter on the continuity (beep) setting and test for continuity between the anode and any exposed metal such as the rear sealing nut, the front sealing nut, any scratches in the black anodized layer and the connectors on the rear bulkhead. If there is electrical continuity between these parts and the anode then the anode will help protect them from corrosion.   


It is helpful to have two purposes for everything you bring with you to sea. In addition to making you look your best on deck, nail-polish is effective as a paint to cover nicks and scratches on your instrument. The pressure tube has a black anodized layer that electrically insulates your instrument from seawater. This insulation helps prevent corrosion of your instrument. When the anodized layer is broken, for example from being scratched by sharp fingernails, the exposed metal will start to corrode. To prevent corrosion of exposed metal, thoroughly wash, and dry off, the damaged spot and surrounding area, then paint over with nail-polish. Black nail-polish is often used for aesthetic reasons, but many users prefer a clear polish to allow periodic monitoring of the site.      


Please note that while fresh water is much less corrosive than seawater, proper corrosion prevention practices should still be followed when operating in freshwater bodies. Aluminum anodes will remain effective in freshwater, however for long-term deployments in freshwater RSI recommends magnesium anodes. Please contact RSI if you would like to discuss the best option for your application.

Maintenance Tips Review

  • Rinse instrument with freshwater after each deployment
  • Ensure instrument is dry before storing for more than 24hours. Remember, corrosion never sleeps!
  • Perform post cruise maintenance and cleaning before long-term storage
  • Check electrical continuity between anode and sealing nuts and any scratches on pressure tube
  • Bend and sand copper tab on rear bulkhead if necessary
  • Paint any exposed metal due to scratching with nail-polish
  • Scrape oxidization off zinc anodes before each deployment
  • If you have a zinc anode please request a replacement aluminum anode from RSI
  • Clean the anode bolt and coat threads with anti-seize lubricant such as Never-Seez to ensure continuity between rear bulkhead and anode
  • Magnesium anodes are recommended for long-term freshwater deployments


Troubleshooting Realtime Instruments

Early morning deployment of VMP-2000 using a Chris MacKay hydraulic winch system aboard the R/V Point Sur, Gulf of Mexico 2017

The Rockland suite of instrumentation includes many realtime instruments including the VMP-2000, VMP-500-RT and the VMP-250-RT. Realtime instruments use an electro-mechanical cable to send data back to the ship in real time. Cables can reach lengths up to 2500m and sending data this distance is no easy task. The strength of the received signal on a communication line decreases with increasing length of the line and bit-rate. You can learn more about the transmission of data and modifying the bit-rate in Technical Note 003 available in the downloads section.

The most common issue with realtime instruments are communication errors known as bad buffers. Bad Buffers occur when a data record sent from the instrument is not interpreted correctly by the receiving computer. The data in the record is lost and the cause of the bad buffers must be investigated. Bad buffers are most often caused by damage to the transmission cable. Cables that have been damaged by anomalously large stresses, such as by bending it around sharp-edged objects, or by excessive twisting and hockling, may still show DC electrical characteristics that are nominal. However, the local discontinuity of resistance, capacitance and inductance will cause a partial reflection of the signals. A reflection reduces the amplitude of the transmitted signal. The reflected signal will probably get reflected back into its original direction of travel (by other discontinuities) and thereby skew the phase of the signal received at the far end. This skewing of phase can be very detrimental. Usually, the maximum stress on the cable is at the instrument end. If a cable, that previously worked well, exhibits progressive deterioration (an increase in the frequency of bad buffers, for example), then it may be necessary to trim off some of the cable at the instrument end, and re-terminate in order to re-establish successful communication. The amount trimmed from the cable is usually 50 to 200 m. The entire length of a cable should also be visually inspected for signs of damage, on a regular basis (such as before every cruise), by spooling the cable from the winch to a holding drum.

Directions for re-terminating (splicing) the instrument end of a VMP cable can be found in Technical Note 014 available in the downloads section.


Powering a MicroRider Instrument: Startup and Shutdown Sequence

The MicroRider is a small instrument package for turbulence microstructure measurements, designed to integrate with a variety of marine instrument carriers, such as Gliders, AUVs, moorings, CTD rosettes, profiling floats and the WireWalker.

Depending on the age if your MicroRider instrument, it will either have an IE55-1206-BCR or a MCBH(WB)-8-FS connect on the rear end-cap.  This connector serves as the power supply, RS232 serial output and ON/OFF signal for the MicroRider. 

To power on your MicroRider, here is the startup sequence:

Using the connection to the IE55-1206-BCR or MCBH-8-MP connector, where:

Pin 1: +12VDC Power
Pin 2: Power Ground
Pin 3: Not Connected
Pin 4: Not Connected
Pin 5: RS232 TX
Pin 6: RS232 RX
Pin 7: ON Signal
Pin 8: ON Signal Return
  1. Connect the Power to Pin 1 and Pin 2. This power must always be available (on and live) to the MicroRider.  The power supply board has a low power watchdog circuit that checks the power. 
  2. If the power voltage is OK (within limits) than the power supply board waits for the ON signal to be activated. 
  3. The ON signal is connected to Pin 7 and Pin 8. It is either done by shorting across Pin7 and Pin8, or by sending a small current (1mA – 2mA) into Pin 7 and return on Pin 8. 
  4. When the ON signal is detected by the power supply board it energizes the MicroRider. 
  5. The internal computer boots up. 
  6. At this time the customer RS232 connection on Pins 5/6 through a terminal program (Motocross) can be made so the customer has manual control of datalogging. Or, the computer can be set up so it automatically starts datalogging. 
  7. To safely shut off the MicroRider the customer must stop datalogging. 
  8. Then remove the ON signal which tells the power supply board to shutdown. 
  9. The MicroRider goes back to the very low power watchdog state waiting for the next ON signal. 

  • Power must always be available 
  • ON/OFF is controlled by the user through a shorting switch or using a small current driver 
  • Datalogging is either started automatically; or the user can manually control through the serial connection. 
  • Power must not be disconnected while datalogging or the onboard computer files will be corrupted and it will not work properly.

Limiting the Size and Duration of Data Files: autoexec.bat

When preparing for a long duration deployment it is important to consider the length of the data file that will be generated. MicroRiders are often deployed for days or weeks at a time. The default setting on RSI instruments is to collect a single data file unlimited in size. A file collected over days or weeks can be unmanageable in post processing. Furthermore, a file can be lost if the instrument is turned off incorrectly while recording. To limit the size and duration of resulting data files use the flag -t followed by the number of records you would like in each file (1 record is approximately 1 second) . Please note that you will loose 30 to 40 seconds of data every time a file is written; users often use 3600 records (approximately 1 hour). To change your system to automatically use the command odas5ir -f setup.cfg -l 3000 -t 3600 you will need to change the autoexec.bat file:

1. Download the file to your data acquisition computer,
2. Edit the contents of the file to be odas5ir -f setup.cfg -l 3000 -t 3600, or the number of records you prefer,
3. Delete the existing autoexec.bat off the CF card,
4. Upload the new autoexec.bat file to the CF card.

Please note the flag -l 3000 sets the clock on the instrument. For instruments with the Tidal Energy Configuration, which use a sample rate of 1024Hz, the clock must be set to -l 6000.

Warning: Commands on the autoexec.bat file are case sensitive.

To learn more about PicoDOS commands, please review the ODAS5-IR User Guide available in our downloads section.

How to Make a Hotel File

MicroRider mounted on an ocean glider

In order to process data from a velocity shear probe the speed of the instrument or flow over the probes must be obtained. When using a Vertical Microstructure Profiler (VMP) the pressure data can be used to determine speed. However, pressure data cannot be used to obtain speed when profiling horizontally with a MicroRider. In most cases, speed must be determined by using an secondary source such as an acoustic doppler velocimeter, an electromagnetic flow sensor or speed records from an AUV or glider.

If your RSI instrument is mounted on a vehicle that provides mission files, you may wish to integrate the data provided in the mission file into your data processing. In some cases the data recorded by the vehicle is required to process the p-file. There are currently four scripts and functions in the ODAS MATLAB Library for extracting information out of mission files and placing it into a hotel file.

The hotel file is ingested by odas_p2mat and interpolated on to the time vector t_slow in your p-file. The resulting data vectors are saved to the same mat-file as the data vectors produced from the p-files. The most common use of a hotel file is to import speed data from a vehicle when the RSI instrument is not able to measure the speed itself (such as an AUV equipped with a MicroRider, or a Seaglider equipped with MicroPods). An accurate speed estimate is required to convert shear probe data into physical units and to compute gradients of temperature and conductivity. Other data of interest measured by the controller in a vehicle include CT data, pressure, pitch, roll and heading, for example.

If you would like to processes your data without a hotel file, please indicate a reasonable constant speed in meters per second. For example: odas_p2mat(‘file_name.P’,’constant_speed’,1.2)

For more information and an example of Hotel File setup, please review Section 10 of Technical Note 39. Please login or register on our website to download this technical note.

Please join us 2017 April 24-27

If you are interested in learning more about Hotel Files, please join us for our annual Ocean Microstructure Glider training (OMG 2017), scheduled for 2017 April 24-27 .

Happy Holidays: Office closed from December 26-30

Please be advised that the Rockland Scientific office will be closed between December 26th to the 30th 2016. Everyone at Rockland wishes you a joyous holiday season especially if you find yourself at sea during this time.

If you require support over the holidays please do not hesitate to contact We will respond promptly to any inquiries.

Happy Holidays from everyone at Rockland Scientific International

Instrument Communication Troubleshooting

While operating a Rockland Scientific Microstructure Instrument you may experience difficulty with instrument communication. Here are some troubleshooting tips to help ensure reliable communication with your internally recording instrument.

In order to communicate, you will need your microstructure instrument, the instrument deck cable and a computer. You will need to connect to your computer via a USB port as well as a 9-pin RS-232 D-sub serial port. If you do not have a serial port on your computer you can use a RS-232 serial to usb adaptor cable. Not all adaptor cables are equal, so if you find one that works well for you then hang on to it!

9-pin RS-232 D-sub serial port

9-pin RS-232 D-sub serial port

RS-232 Serial to USB Adaptor

RS-232 Serial to USB Adaptor

Required Software

There is usually no need to install any software on the Persistor computer in your instrument because this will be done at RSI before the instrument is shipped. However, you must install two programs on your computer. One is Motocross, which provides terminal emulation and serial communication with the instrument and permits the transfer of files, including executable software files. The other is RSI-link, a USB link utility that permits the bi-directional transfer of files between your computer and the instrument. All registered users can download Motocross and RSI-Link as part of a file called ODAS5-IR from the downloads section of our website. To register please fill out the required information under “Register”. You must make an account and receive authorization before downloading.

ODAS5-IR and ODAS5-IR User Manual in Downloads Section

ODAS5-IR and ODAS5-IR User Manual in Downloads Section

Mac vs PC

We recommend using a PC rather than a Mac computer. There are some work-arounds if you must use a Mac. The Motocross Terminal Emulator will not work on Mac computers so we recommend CoolTerm as a replacement for Motocross on Mac computers. CoolTerm allows for reliable communication and file transfers, however it will not allow you to reformat the CF card. For a complete work-around we recommend installing VirtualBox on your Mac and running Windows7.

Which version of windows is preferred?

The following versions of windows are supported: WindowsXP, Windows7, Windows8, Windows8.1, Windows10.

COM Port Number

Motocross has difficulty communicating with serial COM Ports that are not between 1 and 10. If you are having difficulty communicating please check your the serial COM port number and change if necessary. You can access COM ports by opening your Device Manager in the Control Panel while connected to your instrument.

USB 3.0 vs USB 2.0

We are currently experiencing difficulties with instrument communications through USB 3.0. Please use the USB 2.0 port on your computer whenever possible. If you do not have a USB 2.0 port you can use a USB 3.0 to USB 2.0 adaptor cable or hub.

Still having Communication trouble?

Please review your instrument manual and the ODAS5-IR manual or contact us if you would like more information regarding instrument communications.