LabVIEW 1000m below the Waves :
Synchronized Sampling
of Autonomous Units Through Sound
Harald Månum, Senior Engineer at Bjørge AS
Marco Schmid, Senior Engineer at Schmid Engineering AG
Monitoring Gas Extraction In The
Norwegian Sub Sea Is A Worlds First
Fig.1 and Fig.2 © StatoilHydro, Fig.3 © Bjørge
Abstract : Norway’s largest industrial project, ever, development of natural gas extraction in
Ormen Lange, required a condition monitoring system due to the extreme sub sea conditions.
The following solution is an autonomous pipe line free span monitoring system consisting of
several synchronized nodes, analyzing mechanical vibrations and water parameters and
communicating wireless through accoustic modems (Fig.3). It can operate in harsh conditions for
long periods of time, provides high software and hardware reliability, smart error handling and
efficient energy management. The combination of National Instrument's “LabVIEW Embedded
Module for ADI Blackfin” and the Off-The-Shelf Hardware ZMobile based on Blackfin processors
by Analog Devices delivered the stability, versatility, performance and battery life needed to meet
both the time-to-market and quality requirements. The technical solution with very accurate
synchronized sub sea data acquisition is a worlds first. Also new and unique is the applied
graphical programming approach to a large scale application deployed on a low power target.
Zusammenfassung : Gasförderung in der Ormen Lange in Norwegens bislang grösstem
Industrieprojekt erforderte aufgrund extremer Tiefseebedingungen permanente
Zustandsüberwachung. Die vorgestellte Lösung , ein autonomes Pipelineüberwachungssystem,
besteht aus mehreren synchronisierten Knoten, welche Vibrationen und Wasserparameter
analysieren und drahtlos über akkustische Modems kommunizieren (Fig.3). Es kann unter rauhen
Bedingungen über lange Zeiträume eingesetzt werden und stellt höchste Ansprüche an die
Zuverlässigkeit von Hard- und Software, intelligente Fehlerbehandlung und effizientes
Energiemanagement. National Instrument's “LabVIEW Embedded Module for ADI Blackfin” sorgte
zusammen mit der auf Blackfin Prozessoren von Analog Devices basierenden Standardhardware
ZMobile für Stabilität, Vielseitigkeit, Leistung und Akkulaufzeit, die für die Erfüllung der
Anforderungen an Entwicklungszeit und Qualität benötigt wurden. Die technische Lösung
hochpräziser, synchronisierter Datenerfassung in der Tiefsee ist eine Weltneuheit. Das trifft auch
auf die Anwendung grafischer Programmierung für eine Applikation dieser Grössenordnung,
welche auf einem stromsparenden Zielsystem verteilt wird, zu.
Gas Extraction at the Ormen Lange in the North Sea
Development of the Ormen Lange gas field is the largest ever industrial project in Norway,
budgeted with nearly 66 mrd NOK. After starting the production in 2007, it will eventually cover
up to 20% of the British gas consumption for the next 40 years (Fig.1).
The field is situated outside
the Norwegian west coast,
and consists of 24 sub sea
wells in 4 seabed templates.
The gas is transported
through 120km pipelines
from depths down to 850m
to the on-shore production
facilities in Aukra (Fig.2).
Driven by pressure from the
wells only, natural gas is
streamed from underwater
camps (Fig.4) to the surface
through two parallel 30”
pipe lines.
Fig.4 © StatoilHydro
Laying of the pipe lines was however one of the most challenging pipe laying tasks ever done, in
particular due to the rough terrain and sea currents.
Extreme Conditions Require New Solutions
The pipelines traverse the Storegga rock slide. Measuring over 800 km in length, this is one of
the world's longest rock slides on a continental shelf. Rubble has accumulated over thousands of
years, creating an extremely rocky sea bed. Due to this rough terrain, several segments of the
pipe line are not in contact with the sea bed (Fig.5, Fig.6). The strong sea currents may induce
vibrations in these free spans.
Fig.5 : Made from remote operated vehicle (ROV) survey
showing the exact sea bed and as laid Ormen Lange Pipeline
Courtesy: StatoilHydro/Reinertsen
Fig.6: Installation scenario of the free span pipe line
monitoring system on the exact sea bed with a Remote
Operating Vehicle (ROV).
Courtesy StatoilHydro/Reinertsen/Bjørge
Fig.7 and Fig.8 : Photos taken by an ROV showing how the pipeline is laid at the shoulders
between two free spans. Courtesy StatoilHydro
It was thus a direct requirement from the government to have a solution for a vibration
monitoring system to identify movements.
This is why StatoilHydro has installed Bjørge's long-term vibration monitoring system based on
NAXYS technology onto this pipeline before going into production in 2007. The system, realized
with LabVIEW and deployed on a Blackfin target, must survive rough handling from ship deck
cranes and ROV's (Remote Operating Vehicle). Submerged, it faces extreme sub-sea conditions
including low temperatures, no remote power, water avalanches and turbulences due to the
uneven seabed, and changes in internal pipeline flow (Fig.7 and Fig.8).
Pipeline Free Span Monitoring System (PFSMS)
The solution is a sub sea instrumentation network including several autonomous synchronized
“Clamp Sensor Packages” (CSP) and a “Master Sensor Package” (MSP) that monitor vibrations in
longer pipe line free spans.
Despite the extreme environments, the main challenge of this project was to make several nodes
to start and stop logging with a node-to-node accuracy better than 2.5ms over a distance of at
least 100m, as well as simultaneous sampling of 3 analogue channels in parallel to 4 serial IO’s.
As all nodes operate wireless using sound for data transfer and signalling, special measures had
to be taken in the hard- and software design to obtain the required accuracy and deterministic
real time behaviour. A smart energy management scheme ensuring battery power for a minimum
of 6 months life time was another vital design factor. And finally, all the electronics had to fit in
the geometry of a pressure tight pod, ensuring small size and low weight to allow ROV handling.
The final solution based on Naxys technology consists of 4 systems for:
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Multi node synchronized measurement of vibrations in longer free spans, dynamic and
static motion of the pipe line free spans and the measurement of sea-current, -salinity,
-pressure and -temperature
Storage and mathematical analysis of sampled data for up to 6 months
Wireless node-to-node communication
In-node error handling and -recovery for fail safe operation
Acoustic ROV interface for data retrieval and system re-configuration
At least 6 months service interval
Fig.9: Typical sea bed installation monitoring two spans. Courtesy Bjørge
Fig.9 illustrates a typical sea bed installation were one double span is monitored. In this case,
the NAXYS solution also measures the sideways and longitudinal motion of the 30’’ pipe line with
[cm] accuracy.
The CSP's are mounted to the pipeline at regular intervals (Fig.6,Fig.9,Fig.11). Their primary task
is recording vibrations in all 3 axis directions. The mechanics, designed for up to 1500m BLS, is
based on a clamp that can be attached directly onto the 30 inch pipeline by an ROV.
An electronics pod is then mounted on top, using a locking mechanism that allows for later
removal , e.g. for battery replacement. The design allows for easy installation/removal, and yet a
stiff connection, allowing for measuring vibrations as small as a few mg, at frequencies less than
0.1Hz. The CSP's are controlled and synchronized by an inertial MSP tower (Fig.10), installed on
the sea bed by a crane and an ROV. This MSP also records water currents, salinity, temperature
and pressure.
Fig.10 (left) shows a Master Sensor Package (MSP), installed on the sea bed. Courtesy Bjørge. Fig.11 (right) a Clamp
Sensor Package (CSP), mounted on the the pipeline by an ROV. Courtesy StatoilHydro/Reinertsen
Reliable Low Power Battery Operated System with Acoustic
Communication and Built-in Logging
The links between CSP and MSP units are wireless through acoustic modems. The synchronization
scheme is very robust and ensures sampling synchronization even for large and unpredictable
delays in the MSP synchronizing signal, e.g. due to different sound propagation delays. The whole
monitoring system offers three basic modes of operation.
●
Long Term Data logging: The MSP wakes up at a configurable time interval, typically
every 3 hours. At first, it measures the distance to each CSP for compensation purpose.
Following, distributed analogue data recording at 10-20 Hz for 10-30 minutes is initiated
by sending a group call to all CSP nodes. The MSP then starts reading water current,
salinity temperature and pressure through serial interfaces. When logging has finished, the
data is processed and stored to removable memory. After programming the next wakeup,
(RTC) both the MSP and CSP's go to sleep and the whole process is repeated.
●
Event monitoring: A lowest power, intelligent mixed signal circuitry continuously
monitors all vibrations levels for limiting values. If any CSP detects a high acceleration
while asleep, it wakes up and sends a signal to the MSP to initiate the logging scheme.
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ROV rendezvous: The monitoring system is installed and maintained by remote operated
underwater vehicles (ROV, Fig.6 and Fig.11). Through acoustic communication with an
ROV or a top side modem, all vital parameters can be changed at run time, as well as
upload of sampled data or Fourier analyzed data for a requested time period. ROV's are
able to request data from either a CSP or MSP at any time and in parallel to its current
mode of operation. This reliable communication interface is a key feature of the embedded
hard- and software.
Built-in Redundany
Redundancy was a big challenge in this system. Every action is monitored for errors to occur. In
an error case, a node performs a self correction and informs its caller about the situation. All
nodes communicate to decide if the error is within the node itself or any other nodes. If the real
MSP fails, any CSP can become the new MSP to sustain the operation. The pipeline monitoring
system has a lifetime of several years, and will be submerged for at least six months at a time,
thus the highest demands are placed on hard- and software reliability, in-program error handling
and efficient energy management.
Graphical Design of the Embedded System with LabVIEW and
Prototyping with Off-The-Shelf Hardware
Full support for the new graphical embedded system design approach, using LabVIEWTM
Embedded was a key requirement for Bjørge. It helped the system engineers to manage the high
complexity of the application and to meet the challenging project's schedule. Under the hood,
Schmid Engineering's “ZBrain BSP for NI LabVIEW” with its over 200 re-usable embedded
function VI's delivered the necessary real-time features and thread-safe IO libraries.
A synchronized, autonomous system with this accuracy has never been made before and called
for a series of engineering challenges. LabVIEW Embedded, the VDK realtime kernel and the ADI
Blackfin processors resources have been pushed to their limits as the large scale program
demanded for multiple parallel loops (Fig.12), multiple high accuracy interrupts and determinism
of the program execution. The challenges were met and the system may produce an accuracy of
simultaneousness better than the original requirement.
Fig.12: Example of event driven, buffered multiple analog data acquisition on
ZMobile with “ZBrain BSP for NI LabVIEW”, Courtesy Schmid Engineering
The final application equals around 50'000 lines of hand written “C” source code, generates a DXE
executable of 15 Megabytes in size resulting in an Intel HEX loaderfile of 5 MB which is burned
into a 8MB boot flash memory. The application involves typical features of a “cutting edge”
embedded system:
1. Main application tasks implemented by 10 independent Timed Loops / VDK-Threads,
including 4 interrupt callback threads and 2 parallel timed loops
2. Software modularity with more than 100 re-usable sub-modules/sub-VI's
3. Inter-task data communication and synchronization by 5 real time FIFO's, 110 global
variables and 110 VDK semaphores
4. Application logic based on a classic state machine with 16 program states
5. An embedded file handler for configuration files and mass data storage on a
removable 4GB medium (CF-Card)
6. Signal conditioning, max/min and FFT analysis
7. Impulse triggered DAQ synchronization technique with µs accuracy and full
compensation of software latencies and modem propagation delays.
8. Smart power and battery management scheme
9. Programmable Shutdown, Wakeup and Watchdog logic
10.3x simultaneous analog channels to sample a tri-axis accelerometer sensor
11.4x asynchronous Serial IO for measuring water current, salinity, pressure and
temperature
Deploying LabVIEW Application Code to the Low Power Mixed
Signal Platform ZMobile
Each CSP and MSP holds a pod with
all the electronics, batteries, sensors
and acoustic modem antennas
(Fig.13). The pod is water tight and
designed for sea depths down to
1500 meters (150 bar). All internals
are mechanically decoupled from the
vibrations of the pipeline in order to
reduce stress on the components.
The embedded system HW relies on
the compact, low-power target
ZMobile (Fig.14), enhancing a
Blackfin BF533 processor with
versatile mixed signal circuits. Most
of the functionality was already
provided by the Off-The-Shelf
platform. A custom specific add-on
Fig.13: Pressure tight pod showing the electronics. Not visible: battery
board completed all missing circuits,
packs, modem and antennas. Courtesy Bjørge
connectors and interfaces for Bjørge.
This two board approach and combination of standard and customer solution saved precious
engineering time and lowered project risks.
Fig.14 Embedded Hardware : Low-power, Mixed Signal Platform Zmobile based on Blackfin Processors by
Analog Devices and programmable with LabVIEW Embedded, www.zbrain.ch, Courtesy Schmid Engineering
Conclusion
With a project the size of the Ormen Lange and involving tight timelines and rugged conditions,
innovative approaches were required to solve the engineering challenges. Through NAXYS
technology, Bjørge AS was able to solve these challenges by re-using Off-The-Shelf hardware
based on a Blackfin Processor by Analog Devices and applying graphical programming to generate
the code required to deploy to this low-power embedded target. The LabVIEW Embedded Module
helped to shorten development time and ensured parallel operation and complex interrupt
handling demanded for this application.
The oil and gas market now gains from a solution that allows synchronized measuring between 'n'
nodes over distances far longer than 100m with high accuracy. The wireless acoustic
communication, in-node data analysis and storage along with a smart power scheme allows
lowest power consumption and ensures continuous detection and handling of critical static and
dynamic motions . Thanks to acoustic links, critical data can be sent directly to the engineers
desk. This provides new possibilities within all kinds of synchronized vibration monitoring.