AES steps up the pace of control
Rapid response to demanding ventilation requirements is being achieved in a huge car-testing chamber at the Rover Group's Gaydon site in Warwickshire. In particular Trend IQ251 building-services controllers are achieving response times that are not normally required for building-ventilation plant, but at a much lower cost than programmable logic controllers.
Principally designed for measuring car noise levels to ensure that they comply with recent EC legislation for new vehicles, the test chamber measures 30 x 15m and is 6.5m high. Cars are put on a 4roll dynamometer that allows them to be driven at whatever speed; acceleration or deceleration is called for.
Rolton Services Consultants designed the ventilation system.
There are two parts; one provides general ventilation, and the other is for cooling the car and purging the chamber. The general ventilation system supplies fresh air at one end of the chamber, creating a moving front of air, which holds the vehicle exhaust at the other end, from where it is extracted. Air for cooling the car is supplied and entirely or partly extracted via pop-up ducts at both ends of the rolling road. Sophisticated control is required to make the ventilation system work efficiently and to ensure balanced conditions in the sealed chamber, the pressure in which must be kept stable.
The stationary car has to be cooled after every few test to prevent it from overheating. So that the next test can follow quickly, the cooling cycle has to be kept very short. In just a few seconds, the Trend controller has to open the air ducts supply up to 18 m3/s of air, balance the air-extract flow and - on receipt of an operator signal - shut down the fans and close the ducts. The cooling airflow rate and settings such as positions of the duct louvres vary according to the type of car being tested. The values are entered into a 1Q251 via a large operator console, on which pushbuttons are mounted to start and stop the cooling process.
When the supply airflow is over 9 m3/s, which is the maximum capacity of the extract fan, the excess is removed by the main exhaust system. Fan speeds are controlled by inverter drives. To avoid hunting as the fans are brought rapidly up to speed, the controller calculates and generates an inverter output that gets a fan to about the right speed, and then performs fine adjustment based on readings from velocity sensors. The fans are brought to a halt rapidly by direct current injection braking.
If sensors indicate a build-up of carbon monoxide, the operator can initiate a purge cycle that results in all plant being turned to full.
For other tests not involving noise measurement, cooling air is supplied while the car is running. Airflow can be matched to the speed of the car, using a communications link between the dynamometer's programmable logic controller and the Trend controls. The control system, based on three networked IQ251 controllers was engineered and commissioned by AES Control Systems. As well as the main test chamber, they also control heating and air conditioning in ancillary areas and monitor utility meters. Alarms relating to the chamber ventilation are displayed on the local console and also transmitted via the site's Ethernet network to a Trend 945 supervisor in the maintenance office.
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