Originally introduced in the railway industry many years ago, tachographs are devices fitted to large or heavy vehicles to record speed, duty and distance travelled. An analogue tachograph system comprises of a sender unit, tachograph head and a recording medium. In the case of an analogue tachograph, the recording medium is a wax coated paper disc, which is pre-printed with a 24-hour scale.
Analogue tachograph recordings are made by a stylus cutting into a wax-coated analogue chart. Up to three styluses mark the speed, distance travelled, and the driver’s activity. The centre field of the disc is used by the driver to store handwritten information, like the name of the driver, the dates that the disc is recording over, vehicle registration and the start and end odometer readings.
Distance travelled is marked in the closest section to the centerfield; this area is called the distance trace. The stylus will move up and down whilst travelling, producing a zigzag pattern known as a V trace. Each complete V represents 10km travelled, the total distance can then be calculated by counting these zig zags. This is then cross checked and verified by the stated odometer readings.
Driver activity is marked in the mode trace area. It is always displayed as either drive, other work, availability or rest. The activity from the driver is displayed on the chart as a sequence of block traces of differing thickness, with the rest mode being the thinnest line and drive being the thickest.
The last trace is to record the speed of the vehicle. The stylus produces a mark that corresponds with the speed that the vehicle is going at any given time. This is then recorded on a pre-printed speed scale on the disc.
Why are they used?
Since May 2006, Analogue Tachographs have started to be phased out in favour of digital versions, which record data on a smart card. Except in older vehicles, usually those regarded as “Classic Vehicles”, or in some cases buses and coaches, it is rare to find a vehicle that has an Analogue VU installed in an HGV vehicle today.
Analogue units record the driver’s periods of duty on a waxed paper disc – a tachograph chart. An ink pen records the engine speed on circular graph paper that automatically advances according to the internal clock of the tachograph. This graph paper is removed on a regular basis and maintained by the fleet owner for government records.
In the 1950s, there were an increasing number of road accidents attributed to sleep-deprived and tired truck drivers. Concerns for safety led to the rapid spread of the tachograph in the commercial vehicle market, but at this point, it was voluntary and not legislated.
Fleet operators then found that tachographs helped them to monitor driver hours more reliably, and safety improved. In Europe, use of tachographs has been compulsory for all trucks over 3.5 tonnes since 1970.
For safety reasons, most countries also have limits on the working hours of drivers of commercial vehicles. Tachographs are used to monitor drivers’ working hours and ensure that appropriate breaks are taken.
Legislation relating to Tachographs has been in force in the UK for 16 years. The tachograph is now an indispensable tool for managing fleets and ensuring the safety of drivers of commercial vehicles.
There are several different types of Analogue Tachograph VUs however; they all take circular charts as can be seen below. The different types of VU include circular VUs with a lockable face that once unlocked can be opened towards the driver to insert the chart.
Some VUs are of a cassette type. To gain access to the tray to insert the chart, the driver would have to press a button enabling the tray to be released and the chart to be inserted. Once the chart is in place in the cassette, the button was pressed again and the tray would move inside the VU to its position to enable recording the activities of the driver and vehicle.
