On-site calibration keeps airbags on test

When Intier Automotive Interiors needed to have its airbag deployment facility recalibrated, the cost of returning to the US manufacturer was prohibitive.

Intier Automotive Interiors is a global automotive systems group and part of Magna's Intier Automotive.

Intier is at the forefront of the automotive industry trend towards the supply of complete vehicle interiors including cockpit modules, modular door systems and panels, overhead systems, complete seat systems, bespoke seat mechanisms, and closure systems to automotive OEMs.

Intier manufactures instrument panels for cars including Jaguar, GM, Land-Rover and BMW, and recently opened a new environmental test facility - designed to assess the performance of air bag deployment systems - at its UK Technical Centre in Maidstone, Kent.

Its testing services are available to the OEMs directly as well as the automotive supplier community.

With the new test facility, the company is capable of testing and assessing the response of new automotive designs and material developments, as well as product validation.

With a footprint of 2.44 x 2.44 x 2.13m, it can be used for testing full size instrument panels, door, curtain, and seating modules.

The airbag deployment facility enables deployments over the temperature range -40 to +110C, and can offer rapid testing of up to nine deployments in a 24-hour period, all digitally recorded using either an HG 2000 or HG 4540MX frame per second (FPS) cameras or both.

Unlike most deployment chambers, this facility has the feature of preserving product conditioned environmental temperature to within +/-1C at deployment.

The unit was originally supplied, installed and commissioned by a US-based company.

When it was due for recalibration, Intier had to find a supplier capable of calibrating each aspect of the system on-site, as several measurement systems are interrelated.

The high-speed video camera replays footage from the test deployments using its integral clock to determine the all-important delay between triggering the deployment squib(s) and the point at which the bag breaks through the dashboard cover.

The difficult requirement of the calibration was to prove that the video camera synchronises with the triggering signal, which is in turn controlled by a central computer.

Dr John Okello, Product Validation Manager at Intier, needed a supplier who could calibrate the whole unit.

Most companies called in could calibrate all but the critical video timing aspect.

This is where Sira Test and Certification was able to help Intier and the company was appointed to calibrate the airbag deployment unit in December 2001.

Using the original US-calibration certificate for the unit, Sira was able to identify which areas of the machine needed to be tested.

The main problem was how to relate the pulse sent from the computer to the deployment squib(s) to each video frame.

Sira was the only calibration supplier to offer a solution to this problem of determining the synchronisation error.

Intier's on-site airbag deployment unit consists of an environmental test facility large enough to accommodate a full front BIW test buck.

The environmental chamber is mounted on a pulley mechanism to rapidly withdraw from the test assembly before deployment, preventing undue loss of conditioned temperature.

A separate control room houses the data acquisition, control and VDU instrumentation and allows safe viewing of the deployment.

A dedicated computer controls the various parameters critical to the air bag deployment to ensure that they are within predetermined limits and that the safety interlocks are operated before testing of the air bag commences.

Mike Gibbens, from Sira's Electrical Calibration Division, explains: "There were a number of unusual requirements from Intier's calibration project.

Firstly, the calibration had to be conducted on-site because the unit was so large it could not be moved and specific subsystems could not be removed and calibrated in isolation, without compromising the integrity of the measurements.

Secondly, determining the relationship between the video timing signal and the main computer system was not straightforward - this appeared to be the major obstacle for most calibration companies.

This part of the calibration became quite interesting as it involved extensive investigation of the signal paths, system interfaces and interlocks.

It was also useful to have the operating technicians available, as both Sira and Intier were able to benefit from the investigation.

The main challenge for us was to work out how we could get the system to function in the required way in the limited time allowed, as determined by the available budget, without compromising the integrity of the measurements.

Given the advantage of a precisely controlled frequency standard, some bespoke gating circuitry and the innovative use of high-speed optical components, we were able to meet Intier's needs.

This is the sort of challenge we like".

The Sira approach to Intier's requirements reflects Sira's approach to customer calibration per se, "if it needs calibrating, we can find a way to do it".

Dr Okello from Intier adds: "The only other option available to Intier was to fly in a team from the USA to calibrate the unit.

Sira provided a solution that met our requirements, allowing us to keep the unit in use, calibrated and at a competitive price".

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