Context: Inductosense develops patented ultrasonic wall thickness monitoring technology, offering high-resolution, non-destructive asset integrity data quickly and cost-effectively. While successfully commercialised for land-based applications via the WAND Handheld and Remote data collectors, subsea deployment was previously limited to a single-channel, 300-metre-rated prototype validated to ~200m in field trials with Chevron.

The Challenge: The objective of this project was to ruggedise and scale this early proof-of-concept into a commercial-grade, 32-channel, dual-redundant subsea system rated for extreme depths of 3,000 metres. Designed for integration into both mobile Remotely Operated Vehicles (ROVs/AUVs) and permanent subsea installations, the system required an operational lifespan exceeding 25 years. This extreme longevity was non-negotiable due to the prohibitive financial costs associated with deep-sea deployment, maintenance, and equipment retrieval.

• Communication Architecture: Designed the physical hardware layer for a robust 10/100BASE-T Ethernet uplink to the surface operator and integrated universally flexible, fault-tolerant communication protocols (RS-485/422, CAN bus).

• System Reliability: Architected a dual-redundant boot system featuring hardware watchdog logic to guarantee autonomous system recovery in the event of firmware faults.

• Hardware Bring-Up & Signal Optimisation: Directed hardware bring-up and performance characterisation. Diagnosed and resolved critical ultrasonic excitation signal degradation caused by output multiplexers, iteratively tuning the hardware alongside firmware development to ultimately surpass existing commercial baselines.

• EMC Diagnostics & Remediation: Conducted pre-compliance EMC testing, identifying an EN55011 Class B conducted emissions breach. Traced the noise to the DC power supply’s third harmonic switching frequency using a Vector Network Analyser (VNA) and E-field probes, successfully mitigating the issue with low-cost MLCC suppression prior to final qualification.

• Compliance & Longevity: Executed comprehensive API 17F regulatory compliance testing, encompassing environmental EMC, hyperbaric, and thermal certifications. Gathered data for Failure In Time (FIT) analysis to mathematically validate the targeted >25-year operational lifespan.

• Mechanical & Thermal Integration: Reviewed the custom mechanical card frame assembly and guided thermal heatsink integration through detailed thermal profiling and high-performance gap pad selection.

• Manufacturing Governance: Oversaw component staking and conformal coating for moisture isolation, alongside authoring formal assembly and environmental test procedures.

System Architecture & Redundancy: The architecture was anchored around a dual-redundant topology to guarantee continuous operation in deep-water environments. The main pressure vessel was designed to house two fully independent, identical hardware stacks (Stack A and Stack B), allowing immediate failover in the event of a primary hardware failure. To ensure autonomous self-recovery, a robust dual-boot mechanism was engineered. This fail-safe architecture allowed the system to automatically recover from operational crashes, boot from a secondary flash memory if corrupted firmware was detected, and revert to a secure backup firmware version if an update failed.

Scaling & Physical Packaging: Scaling the technology from a single-channel prototype to a 32-channel commercial product introduced severe packaging challenges. Each ultrasonic channel required two twisted pairs (TX/RX), resulting in 128 individual signal cables. Routing this density of wiring—while ensuring the assembly could survive rigorous hyperbaric, thermal, and vibration qualification testing—became the primary mechanical driver. Ultimately, the necessity for large, Commercial Off-The-Shelf (COTS) endcap connectors rated for 3,000 metres dictated the overall dimensions of the pressure vessel.

Standardisation & Universal Compatibility: Because the large connector footprint provided ample internal volume, PCB dimensions were not strictly constrained. Consequently, the custom electronics were strategically standardised to the Eurocard footprint (100mm x 160mm). This aligned the hardware with standard Subsea Electronics Modules (SEM), ensuring seamless adaptability for future legacy upgrades. Externally, the vessel integrated with a dedicated reader head and docking station assembly. To ensure universal compatibility across diverse ROV, AUV, and permanent seabed installations, the communication infrastructure was designed to natively support RS-485/422, fault-tolerant CAN bus, and 10/100BASE-T Ethernet.

Initial bring-up of the hardware got underway in the lab, each board was inspection for manufacturing defects and initial turn on. The analogue and digital board were tackled in different ways alongside the software team developing the firmware for the digital board. The analogue board could be connected to the digital board from the first prototype with dupont style connectors enabling us to drive the excitation signal and and measure the response on an oscope. A secondary bread board with an STM32 nucleo was connected to switch the multiplexers, python scripts were used to change channels prior to each test (prior to the firmware existing for the digital board).  Both the boards needed thermal profiling to steer the design of the custom heatsink.

We had one issue with a voltage regulator on the digital board being too close to its dropout voltage, causing intermittency. A new part was easily identified to resolve the issue.

While work progress was made being made on the analogue board the software team were developing the firmware for the digital board.

It was understood from the prototype build that