A test track, six units and one megahertz

The context

Sector

National test centre, Europe

Platform

High-speed test track, several kilometres

Scope

Acquisition system replacement, open tender

In service

2024 — previous ETEP system since 2016

A high-speed track provides a controlled environment for impact, aerodynamic and acceleration testing: a test item is accelerated along a rail over a known profile, and everything that happens to it has to be measured. The specimens are instrumented, and so is the track.

The centre had been using an earlier ETEP recorder on the specimens since 2016. When the track acquisition itself came up for replacement, it went out as an open tender.

The constraint: a megahertz, spread over kilometres

Two requirements pulled in opposite directions. The interesting phenomena — impacts, shocks, pressure transients — need sampling in the hundreds of kilohertz and up to a megahertz. And the sensors are distributed along a track measured in kilometres, which makes long analog runs impossible: at those rates, cable length is not a nuisance, it is the measurement.

So the acquisition had to be next to the sensors. Which immediately creates the real difficulty: six independent units, each sampling at a megahertz, whose samples must be comparable to each other. At that rate, a microsecond of misalignment between units is a sample.

The architecture

Six units distributed along the track, each carrying ten acquisition modules, linked by a dedicated network switch to a master unit which handles the recording in IRIG 106 Chapter 10 and the real-time transmission to the control room. One time reference, distributed to all six.

The operators see the run as it happens rather than after it, which on a facility where a test consumes the specimen is not a convenience: it is how you decide whether the next run can proceed.

The channels

Roughly a hundred and thirty parameters in total — a small count next to a flight-test installation, at rates two orders of magnitude higher. That inversion is characteristic of ground test facilities, and it is why sizing from a channel count alone gives the wrong answer.

What it changed

The decisive argument in the tender was not the sample rate, which several systems can reach. It was doing it in six places at once with a single time base, and showing the result in the control room while the run was happening.

What we take from it

Ground test facilities look like a simpler version of flight test and behave like the opposite: few channels, extreme rates, short events, and no possibility of repeating the run. Everything that flight test solves with margin, a track has to solve with precision — and the time base does most of the work.