Keeping compressed air monitoring honest when the network drops out
The DOCA Project builds an optical sensor that detects oil contamination in high-purity compressed air, in liquid, aerosol, or vapour form. It matters most where a single misread can compromise a pharmaceutical batch or a hospital's air supply. Catching contamination is one thing; producing a verifiable record is another.
Across much of Australia, the networks that carry those records are far from bulletproof. A compressor hall in the Pilbara, a packaging plant outside Townsville, or a hospital service yard in western Tasmania often depends on a single fixed-wire link or a 4G modem on the roof. Drop-outs are part of the working week, not an exceptional event.
For manufacturers regulated by the Therapeutic Goods Administration, every missed reading becomes a documentation problem. Fair dinkum, regulators will ask why a known gap was not flagged and reconciled. The DOCA consortium treated that reality as a design constraint from day one.
The team's response is a layered approach to data continuity: local buffering, intelligent interpolation, and a reconnection protocol that preserves the timeline of every measurement.
Why compressed air sensors lose data during outages
A compressed air line running at seven bar does not pause because the router rebooted. The optical sensor keeps scanning the airstream, registering absorption spectra, and converting those readings into oil concentration values. The bottleneck is usually the upstream path to the historian, dashboard, or cloud. When the link drops, the sensor keeps measuring but cannot publish.
The interruption can be as mundane as a Telstra tower maintenance window in a regional centre, or as disruptive as a fibre cut during a flood event. Remote mine sites often run on microwave backhaul that flickers in heavy rain.
Typical triggers in Australian industrial settings
- Scheduled maintenance on regional mobile towers serving Pilbara and Hunter Valley sites
- Storm-related fibre damage along coastal corridors between Sydney and Brisbane
- Microwave backhaul degradation during electrical storms in the Top End
- Power cycling of on-site routers during generator changeovers at remote plants
- Bandwidth contention on shared links at hospital and university campuses
Buffering at the edge
The DOCA sensor stores readings in non-volatile memory the moment they are taken. Each record carries a timestamp, a measurement value, a confidence flag, and a quality indicator describing the optical conditions at capture. Storage is sized for days, not minutes.
On reconnection, the device negotiates with the central server and replays its buffer in chronological order. The server validates the sequence, removes duplicates from partial transmissions, and stitches the recovered data into the existing trend.
Filling the gaps with interpolation
A short drop-out of a few minutes rarely needs more than a straight-line bridge between the last good reading and the first one after reconnection. The DOCA software applies that automatically and flags the synthesised section so it cannot be mistaken for live data.
Longer interruptions call for something smarter. The system uses a short history of normal operating patterns, combined with the current compressor load signal, to estimate how oil concentration would have behaved across the gap. Engineers can accept the estimate or replace it with a manual entry.
Reconnecting without losing the plot
Time synchronisation matters when readings from multiple sensors are combined. Each DOCA unit holds an internal real-time clock disciplined by Network Time Protocol whenever a connection is available. During an outage the clock free-runs on a temperature-compensated oscillator, keeping drift to a few seconds per day.
On reconnection the server reconciles timestamps across the fleet and flags any device whose clock has wandered beyond a defined threshold. A technician can trigger a manual resync, or the device self-corrects on the next successful handshake.
Built for Australian conditions
Designing for Sydney's CBD is straightforward. Designing for a compressor skid 80 kilometres off the Stuart Highway is not. The DOCA hardware uses industrial-grade components rated for temperature swings, vibration, and the electromagnetic noise around variable-speed drives. The firmware tolerates flaky links without thrashing storage or flooding the network with retry storms.
The project drew on Australian Standard AS/NZS ISO 8573 for compressed air purity classes, which shaped the sensor's dynamic range and the granularity of its data logging. Field trials in Melbourne and Adelaide validated the reconnection behaviour under realistic network conditions, including simulated tower outages.
Design choices shaped by local realities
- Wide-input power supplies that ride through generator transitions
- Conformal coating for humidity at coastal plants
- 4G, Ethernet, and satellite fallback paths in one telemetry module
- Local display option for sites that stay offline for days
- Automatic log rotation suited to low-cost edge hardware
Meeting TGA and pharmaceutical standards
Documentation is the lifeblood of pharmaceutical manufacturing, and the Therapeutic Goods Administration expects a defensible record of every critical parameter. A gap in compressed air monitoring can ripple through batch release decisions, particularly for sterile products where oil contamination above the class 1 limit is a hard stop.
The DOCA Project built its data handling so that gaps become first-class objects in the audit trail. Each gap carries a start time, end time, cause category, recovery action, and a digital signature from the responsible operator. That structure aligns with Good Manufacturing Practice audits and gives quality managers something concrete for inspectors.
From pilot to production across Australia
The consortium is moving from controlled trials to multi-site pilots with partners in the food, hospital, and electronics sectors. Each pilot will exercise the buffer-and-replay workflow under genuine operational load, including the kind of network blips that tradies and technicians would normally shrug off with a "she'll be right".
If the pilot phase holds up, the next step is integration with plant historian systems used by Australian manufacturers and a licensing pathway that lets local system integrators offer DOCA-enabled monitoring as a service. The aim is a sensor that any plant operator from Perth to Parramatta can install without worrying about what happens when the link drops.
Want the full technical specification and latest test results? Visit the DOCA Project resources page to download the work package deliverables and join the industry mailing list.