PID controller at heart of jaguar test system

Edited by the Engineeringtalk editorial team Oct 9, 2001

To ensure that vehicle airbags operate reliably across a variety of environmental conditions, Jaguar Cars commissioned a sophisticated environmental chamber featuring Eurotherm control

To ensure that vehicle airbags operate reliably across a variety of environmental conditions, Jaguar Cars commissioned a sophisticated environmental chamber from West Sussex based Temperature Applied Sciences (TAS) to form a vital part of a new test facility.

The facility, located at Jaguar's Whitley Engineering Centre, Coventry, will be used for all current and future models of Jaguar car, and automatically tests airbags for correct deployment within a wide range of temperatures, humidity, and solar radiation conditions.

Sited within a sound-proofed room, the insulated 23,100 litre (816 cu ft) Airbag Deployment Chamber is designed to simulate exterior climatic conditions world-wide, and also the extreme conditions which can be found within vehicle interiors.

The variable environmental parameters within the chamber include a temperature range of -40C to + 120C, humidity from 10 to 98%, as well as variable solar load simulation provided by infrared lamps.

The lamps are mounted on an adjustable framework, which can be used either inside or outside of the chamber.

An automated handling system arranges for the airbag assemblies under test to be deployed under the set conditions.

The main chamber access doors are automatically operated by a rugged power closure system, which ensures excellent sealing.

After opening, a separate pneumatic system retracts the door from the face of the chamber and provides clear access.

With the main door opened, a chain driven extraction/retraction system propels a sled supporting the airbag test frame outwards into the deployment area, which consists of a raised platform at the same level as the chamber floor.

The test frame is securely attached to the sled to limit reaction movement during deployment.

The pyrotechnic devices being tested are first stabilised within the closed chamber at the set conditions, before being automatically removed and deployed in the shortest possible time.

A remote signal causes the chamber doors to open automatically and the sled to be extracted, a further signal being provided from the chamber upon completion.

The automated system minimises the removal time and effort and thus provides repeatable results.

Accurate feedback control of the three environmental parameters (temperature, humidity and infrared radiation) is achieved using a standard Eurotherm type 2704 triple loop PID controller.

The 2704 is a high stability multi-loop temperature and process controller with a high visibility graphical user interface.

An optional setpoint programming function allows storage of up to 50 programs, each program being capable of profiling up to three setpoints.

Using the 2704's internal Toolkit Blocks, customised user configurations can be created.

Within this particular application, standard RTD and humidity sensors are used, and the feedback loop for the infrared radiation is provided by a black panel sensor, mounted near to the pyrotechnic device under test.

Other parameters within the system are monitored and controlled via a separate 16 way data-logging system, which picks up signals from 12 movable thermocouples within the chamber temperature and a humidity sensor.

An infrared pyranometer, measuring delivered Watts/m2 provides a visual indication of solar heating.

The system is capable of steady state operation and cycling, being programmable directly from a PC sited in an adjacent room.

This interface, which utilises specially developed software, also permits the recording of set and actual temperatures during a test.

Tim Stevens, Technical Director of TAS, believes the test facility is amongst the most advanced in the industry.

He comments: "Jaguar Cars have a well-deserved world-wide reputation for product quality, performance and passenger safety, and we are very pleased to have been able to play a part in this.

The air bag deployment rig we designed and built is the most advanced of its kind anywhere, and ensures that the reliability of these vital passenger safety devices is consistently maintained.".