Distance pulse number

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Distance covered (W = 980) in the speedometer of an Audi 80 B2
Distance traveled (1.25) on a BMW R26

Distance pulse number , also tacho constant or device constant (depending on the manufacturer, also k-number ( K-number ), nowadays rather seldom route number , distance speed or distance ) is the ratio between the number of pulses or, in older vehicles, the number of revolutions in vehicle and drive technology a speedometer shaft and the distance covered . It depends on the wheel size and the ratio to the drive shaft or to the speedometer shaft drive. The number of distance pulses is one of the decisive factors for the accuracy of the display of the speedometer and odometer .

The distance is given as a value on old mechanical speedometers, for example "W = 715" means that for every 1000 meters covered there are 715 revolutions of the speedometer cable. Other manufacturers sometimes use a different symbol k (instead of w or W ). The accuracy of the distance measurement in an odometer is subject to legal requirements in Germany. According to Section 57 (3) StVZO, the deviation may be +/- 4%. For the speed measurement of the tachometer, it applies that the displayed speed is not below the actually driven, but upwards by max. 10% v + 4 km / h (so-called speed advance).

In the case of electronic tachometers, as they are installed today as part of the instrument cluster in automobiles, the number of travel impulses is often a value that can be subsequently adjusted by the workshop service computer and is stored in an EEPROM , for example . Such a change is usually necessary when fitting a different tire size with a slightly different diameter . The number of distance impulses programmed into the speedometer can be read in some vehicles via a hidden menu item in the instrument cluster. The wheel speed required to calculate the distance and speed is measured with an incremental encoder .

According to Annex XVIIIa to Section 57b, Paragraph 1 of the StVZO , the number of distance impulses w is determined by rolling on a flat test track of at least 40 m; Alternatively, a 20 m long measuring section can be selected when using an electronic distance pulse rate measuring device or a suitable roller test bench. The number of pulses on the defined measuring section is determined; accordingly, the unit of measurement from w to [impulses / kilometer] or [I / km] results . In English-speaking countries, the number of impulses is given in the unit "pulses per mile" [PPM].

For example, for the approval of video tracking systems and associated speed measurement devices in motor vehicles (for official speed monitoring), the PTB requires that the distance pulse generator can deliver at least 2000 l / km.

Definitions according to ECE-R 39

In the regulation, the "device constant of the speedometer" is defined as the "ratio between the number of revolutions or pulses per minute at the input and a certain displayed speed". The "device constant of the odometer" is defined as the "ratio between the number of revolutions or pulses at the input and the distance covered".

See also

Web links

Individual evidence

  1. ↑ ECE regulation No. R 39 - Uniform provisions concerning the approval of vehicles with regard to the speedometer and odometer equipment including its installation
  2. ↑ https://www.zwiki.net/index.php/Geheimmenu
  3. ↑ https://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_1/1.3_kinematik/1.31/PTB-Anhaben/PTB-A_18.3.pdf