Impact Subsea explores the ISA500, the world’s first combined altimeter with an in-built HMRU
In the current energy market, demand for intelligent solutions is at an all-time high. A decade of high oil prices has allowed many to overlook inefficiencies in underwater operations caused by imperfect technical solutions. New innovations in underwater technology are in demand to provide increased efficiency and decreased operational costs.
Altimeters are one component which has suffered from stagnated interest. Despite major advances in microelectromechanical (MEMS)-based sensors and their capabilities, the past decade has seen comparatively few changes to altimeter design and functionality. Harnessing these improvements will allow users to make remotely-operated vehicle (ROV) operations more efficient, precise and accurate.
Impact Subsea was established in Aberdeenshire in early 2015 by an experienced team of underwater technology developers. The company was founded with the core aim of reducing the cost of underwater operations using a new generation of highly innovative product solutions.
The company launched its first ground-breaking innovation in August 2015 – the ISA500.
The ISA500 is the world’s first and only hydro-acoustic based underwater altimeter with an in-built heading and motion reference unit (HMRU). It provides an all-in-one solution for ROV and AUV altitude, heading, pitch and roll monitoring, at approximately half the cost of purchasing a comparable stand-alone altimeter and HMRU.
The ISA500 provides a 120-metre range capability, coupled with pinpoint accuracy (effective to the nearest millimetre). This sets a new standard in range and accuracy for 500kHz underwater altimeters, as well as a significant saving on space and equipment in the vehicle itself.
This range increase is achieved through the use of a highly sensitive directional piezo-composite transducer, the component which produces the hydro-acoustic pulse and listens for the return pulse. The transducer’s composite design then allows the unit to detect smaller return signals, enabling an increase in range capability.
An advanced digital correlator is used to detect the returning pulse. The correlator can detect very low signal to noise pulses, greatly helping to provide a long-range capability while maintaining an exceptional level of measurement accuracy.
Enclosed within a titanium housing as standard and depth rated to 4,000 metres (400 bar/5,800 psi), the ISA500 is built to withstand the harshest of underwater conditions. Its unique design uses no screws in the outer housing – removing the potential corrosion, fouling and weakness issues often associated with screw-fixed units.
Weighing 0.5kg in air and 0.325kg in water, the ISA500 is light enough for use in some of the smallest AUVs, but robust enough to handle the demands of larger work-class vehicles.
Heading, pitch & roll
The design team at Impact Subsea were keen to ensure that the ISA500 provided more than purely altitude. With significant developments being made in MEMS-based sensors in recent years, the team decided to integrate magnetometer, gyro and accelerometers based on this technology into the unit.
The magnetometer enables a magnetic north heading to be determined to accuracy of within +/- 1°. This value is fed into the gyro, adding significant increased stability to the heading and producing a far more stable result than that produced from flux-gate compass-based devices.
To further increase heading accuracy, a calibration feature is provided in the ISA500. Once the unit is installed in a subsea vehicle, calibration can be carried out to minimise the effects of permanent hard and soft iron.
Accelerometers and gyroscopes in X, Y and Z planes are fused together to provide highly accurate pitch and roll readings, to within 0.2°.
The ISA500 also has the ability to correct for slant range measurements caused by vehicle pitch and roll. The unit can take into account these pitch and roll readings and combine them with its range reading to calculate actual altitude, to within a few centimetres.
This results in a very smooth and very accurate altitude reading at all times, regardless of the pitch and roll of the vehicle – another true first in underwater altimeter technology.
Initially designed to be an ideal sensor for ROV & AUV applications, the ISA500 has found uses in various other underwater applications as well.
In one instance, the ISA500 was used to monitor not only the height above seabed of a ROV tether management system (TMS), but also to log its motion while subsea. This ability enabled additional monitoring to be carried out, allowing users to calculate and examine the long-term fatigue data on the TMS.
Altimeter units have been used for a long time to monitor the deployment of various assets and tools. Traditional altimeters measure just the depth range, with no indication of the tool or asset’s orientation. With the ISA500, a far higher degree of understanding of the height above seabed, orientation, pitch and roll of the tool/asset is provided. This significantly reduces risk when deploying the asset and in some instances can also reduce its deployment time.
The ISA500-L – a pure altimeter – has also been designed to be as flexible as possible in order to meet individual requirements. Available with various connector options, physical connection to any system is as simple as possible, the ISA500-L features the exact same measurements and specifications as the original, without the integrated HMRU.
Furthermore, the system is provided with an in-field firmware update feature to add new output strings and capability. This ensures that the unit can be easily adapted to suit any underwater altitude or distance measurement application.
With numerous work-class ROV and AUV manufacturers now integrating the ISA500 into their new vehicles as standard, the unit has been well received by the underwater vehicle market. Discussions are under way with several manufacturers, while other early-stage work could see the company integrate its OEM components directly into the housings of new micro-ROVs.
Impact Subsea is now focusing on its next product – the ISD4000. The unit is set for launch early February 2016 and will be premièred at SubseaExpo in Aberdeen, taking place on February 3-5.
In-depth details of the ISD4000 will be released at launch. However, InnovOil is pleased to disclose that the unit will provide a significant breakthrough in the underwater depth measurement market.
Impact Subsea will be showcasing the ISA500 and the brand-new ISD4000 at Pod 173 of Subsea Expo