2.1) The Digital Tachograph Vehicle Unit (VU)

The Digital Tachograph Vehicle Unit (VU)

The Digital Tachograph Vehicle Unit (VU) is an electronic device that is able to record
and store driver and vehicle records. The VU must have the ability to store this data for
at least 365 days and must make it possible to download that data. Operators based
in Great Britain are obliged to download the data at least every 56 days, and then
store it safely and make it available for inspection by the authorities for the next
twelve months.

Data recorded by the VU include vehicle speed, distance travelled and other system
related parameters. General vehicle speed data is limited to 24 driving hours and is
recorded only in the memory of the Digital Tachograph Vehicle Unit. It is NOT written
to the Driver Card. Details of excessive speeds (overspeeds) are recorded however,
and analysis of the data can show these events and other useful information such as
‘harsh braking’.

Even if the external power supply to the VU is removed, (for example, If the vehicle
batteries are disconnected for maintenance), the VU is still able to store data as it is
fitted with its own internal battery that must be able to provide power for at least two
years. As such, there should not normally be any need to have the internal VU clock
reset between calibration dates, which are every two years rather than the six year
period for analogue equipment.

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