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5. Definition of the terms Speed and Impulses per rotation.
The speed of a engine is the number of crankshaft rotations per minute.
In diesel engines, the speed, when present, can be taken from the "W" terminal of the generator.
There is a potential for inaccuracy due to the V-belt slip. An initiator (pick up), on the other hand, re-
turns absolute values (comply with the manufacturer's installation instructions).
In both cases, frequency (impulses per second) is used. The frequency of these impulses is propor-
tional to the engine speed.
5.1 Speed measurement using the impulses of the "W" terminal.
To determine the frequency ("W" generator terminal), you must know two factors. The transmission
ratio of the generator to the crankshaft which can be calculated as follows:
Transmission ratio (i) =
and the number of pole pairs of the generator. At the front end of the generator, claw-shaped poles
are visible that are placed next to each other alternating as North and South poles. Halve the number
of these pole and you obtain the number of pole pairs (see below). For the Bosch types G1, K1 and
N1, there are six pole pairs and 8 pairs for the Bosch type T1.
When the transmission ratio and the number of pole pairs are known, you can calculate the number of
impulses per rotation (IPU) according to this formula:
IPU= i x pole pairs
5.2 Speed measurement using an initiator
The initiator must be at a right angle to a rotating metallic component which is directly connected to
the engine's crankshaft. This can be a belt pulley or the flywheel of the engine, for example. The sys-
tem captures bores or protrusion such as screw heads. The distance must be the same and within the
capturing range of the initiator. When installing the initiator, ensure that multiple impulses (ideally 4 to
16 impulses) are emitted for each engine rotation per crankshaft rotation. The number of impulses
should not be too low as this would result in a low resolution.
This method is suitable for applications requiring an accurate capture of the speed or when the gener-
ator is not fitted with a "W" terminal.
© ehb Errors expected.
Operating Instructions
Diameter belt pulley crankshaft
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Diameter belt pulley generator
Schematic design of a generator
Version 2.9.4
pick up)
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