It is in VSS possible for signals to specify a unit of measurement from a list of predefined data unit types.
For most signals in the VSS standard catalog, a data unit type has been selected. A typical example is
Vehicle.Speed, as shown below.
Vehicle.Speed: datatype: float type: sensor unit: km/h description: Vehicle speed.
The ambition when selecting data unit types for signals in VSS standard catalog has been to use either a unit based on SI-units,
or a unit commonly used within the vehicle industry. For the
Vehicle.Speed example above this means that
km/h has been selected,
m/s from an SI-perspective would have been a better choice.
It must be noted that the selected unit does not imply that the value of
Vehicle.Speed always needs to be sent or visualized
km/h (with float as datatype). A user interface or API may show or request vehicle speed in any unit it likes,
and a transport protocol may send speed in another unit, possibly also involving scaling and offset.
But in protocols not explicitly specifying data unit types (like VISS)
it is expected that
Vehicle.Speed is sent and received as
km/h (without scaling or offset).
In some cases it is natural to omit the data unit type. This concerns typically signals where data type
string is used,
but also signals where the value just represents a number, like in the example below:
Vehicle.Cabin.DoorCount: datatype: uint8 type: attribute default: 4 description: Number of doors in vehicle.
percent as data unit type, typically with 0 to 100% as the allowed range.
In some cases, the definition on how to calculate the signal value is obvious, like for
below. It is likely that all VSS users will calculate fuel level in the same way, i.e. the meaning of a fuel level of 50%
is well agreed, the liters of fuel in the tank is exactly 50% of nominal capacity.
Vehicle.Powertrain.FuelSystem.Level: datatype: uint8 type: sensor unit: percent min: 0 max: 100 description: Level in fuel tank as percent of capacity. 0 = empty. 100 = full.
In other cases, the formula for calculating the signal is not obvious and is not specified in VSS. A typical example is shown below for clutch wear. While most VSS users likely can agree that a brand new clutch shall have 0 as “ClutchWear”, the exact formula for calculating clutch wear for a used clutch will likely be vehicle specific. Some vehicles might monitor actual wear, others might estimate it based on vehicle usage. This is in VSS called a logical range, a VSS user knows what range to use but are free to define the formula for calculating the value. Values from different vehicles (of different make/model) can not always be compared, as the formula used for calculation may differ.
Vehicle.Powertrain.Transmission.ClutchWear: datatype: uint8 type: sensor unit: percent max: 100 description: Clutch wear as percent. 0 = no wear. 100 = worn.
|mm||Distance||Distance measured in millimeters|
|cm||Distance||Distance measured in centimeters|
|m||Distance||Distance measured in meters|
|km||Distance||Distance measured in kilometers|
|inch||Distance||Distance measured in inches|
|km/h||Speed||Speed measured in kilometers per hours|
|m/s||Speed||Speed measured in meters per second|
|m/s^2||Acceleration||Acceleration measured in meters per second squared|
|cm/s^2||Acceleration||Acceleration measured in centimeters per second squared|
|ml||Volume||Volume measured in milliliters|
|l||Volume||Volume measured in liters|
|cm^3||Volume||Volume measured in cubic centimeters|
|celsius||Temperature||Temperature measured in degree celsius|
|degrees||Angle||Angle measured in degrees|
|degrees/s||Angular Speed||Angular speed measured in degrees per second|
|W||Power||Power measured in watts|
|kW||Power||Power measured in kilowatts|
|PS||Power||Power measured in horsepower|
|kWh||Energy Consumption||Energy consumption measured in kilowatt hours|
|g||Weight||Mass measured in grams|
|kg||Weight||Mass measured in kilograms|
|lbs||Weight||Mass measured in pounds|
|V||Electric Potential||Electric potential measured in volts|
|A||Electric Current||Electric current measured in amperes|
|Ah||Electric Charge||Electric charge measured in ampere hours|
|ms||Time||Time measured in milliseconds|
|s||Time||Time measured in seconds|
|min||Time||Time measured in minutes|
|h||Time||Time measured in hours|
|day||Time||Time measured in days|
|weeks||Time||Time measured in weeks|
|months||Time||Time measured in months|
|years||Time||Time measured in years|
|UNIX Timestamp||Time||Unix time is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, excluding leap seconds.|
|mbar||Pressure||Pressure measured in millibars|
|Pa||Pressure||Pressure measured in pascal|
|kPa||Pressure||Pressure measured in kilopascal|
|stars||Rating||Rating measured in stars|
|g/s||Mass per time||Mass per time measured in grams per second|
|g/km||Mass per distance||Mass per distance measured in grams per kilometers|
|kWh/100km||Energy Consumption per distance||Energy consumption per distance measured in kilowatt hours per 100 kilometers|
|ml/100km||Volume per distance||Volume per distance measured in milliliters per 100 kilometers|
|l/100km||Volume per distance||Volume per distance measured in liters per 100 kilometers|
|l/h||Flow||Flow measured in liters per hour|
|mpg||Distance per Volume||Distance per volume measured in miles per gallon|
|N||Force||Force measured in newton|
|Nm||Torque||Torque measured in newton meters|
|rpm||Rotational Speed||Rotational speed measured in revolutions per minute|
|Hz||Frequency||Frequency measured in hertz|
|ratio||Relation||Relation measured as ratio|
|percent||Relation||Relation measured in percent|
VSS tooling use the list specified in config.yaml to validate that only supported types are used in the signal specification.