To ensure that the seating arrangement is correctly set up for each individual occupant, heavy goods vehicle drivers are being cared for by potentiometers. The devices are being used for monitoring the position of the driver’s seat. The information provided by the units is used by a microprocessor to ensure that the seating position is correctly set up for each individual driver. The arrangement is said to save effort, reduce tiredness and make a significant contribution to safety.
Environmental conditions under which the seat position sensors operate, especially when the vehicle is on the move, vary tremendously, as they range from vibration, shock, freezing temperatures at night and high temperatures during the day. An additional problem is the fact that vehicle supply services, such as electrics, are occasionally disconnected.
Properly used, conductive plastic potentiometers have proved ideal for this application since they are virtually unaffected by changes in temperature and humidity. Furthermore, as absolute devices – they know where they are at all times – if the seat is moved while the battery is disconnected, the sensor still knows where it is. When power is restored the seat automatically returns to its last programmed position.
Potentiometers are extremely versatile and come in all shapes and sizes. The unit used on the lorry seats is of a `hollow shaft’ construction, this being dictated by the `scissors’ type action of the seat height adjustment. As the `angular’ relationship of the `scissors blades’ is directly related to the seat height position, this was the best point to fit a sensor.
The Contelec model WAL300 was mounted directly to the blades without the need for special gears or drive mechanisms, and as it is so thin that it requires very little space. It has no stops and operates over a 30 degrees to 340 degrees range, which the seat adjustment required. The sensor offers virtually infinite resolution and repeatability to within 0.2%.
The automotive industry is renowned for its demanding specifications and that they are met. The testing programme for the WAL300 was no exception, calling for over 10 million `dither’ cycles when operated over a limit of 20 degrees. It passed all tests with flying colours and seats incorporating the new sensors are being produced and fitted into fully operational vehicles.
Variohm Components Tel: 01327 351004