Operating instructions
HMCflex
19/23
© ehb errors and omissions excepted
5.1 Speed measurement through the impulses of terminal "W"
In order to be able to establish the frequency (alternator terminal "W"), two factors must be known. On
the one hand, this involves the transmission ratio from the alternator to the crankshaft, which you can
calculate as follows:
Diameter belt pulley crankshaft
Transmission ratio (i) = ----------------------------------------------------------------
Diameter belt pulley alternator
and on the other hand the number of pole pairs on the alternator. Claw-shaped pole fingers are visible
from the front of the alternator, which are located next to one another, alternating between north and
south poles. The number of these pole fingers should be halved in order to get the number of pole
pairs (see below). The values for the number of pole pairs are 6 for Bosch types G1, K1 and N1 and 8
for the Bosch type T1.
Once both the transmission ratio and the number of pole pairs are known, then the number of pulses
per revolution (PPR) should be calculated according to the following formula:
PPR= i x pole pairs
Schematic layout of an alternator
5.2 Speed measurement through a pickup
The pickup must be in the right corner of a rotating metal part, which is directly connected to the
crankshaft of the engine. This can for instance be a belt pulley or the engine's flywheel. Holes and
elevations, e.g. screw heads, are recorded. The spacing must be equal and within the pickup's cover-
age. When fitting the pickup, care is to be taken that, per revolution of the crankshaft, several pulses
are delivered per revolution of the engine (optimum values are 4-16 pulses). You should not choose a
number of pulses that is too low, as then only a low resolution is given.
This method is suitable for applications, where a precise recording of the speed is involved or when
the alternator does not have the "W" terminal.
6 Description of temperature-dependent preheating
The HMCflex supports temperature-dependent preheating. The two temperatures temp1 and temp2
give the temperature range in which temperature-dependent preheating is carried out. The HMCflex
independently recognises the upper and lower values from the two values, temp1 and temp2. Only the
glowtimes timetemp1 and timetemp2 have to be programmed according to the temperatures temp1
and temp2. For temperatures below the lower programmed temperature, the HMCflex retains the
glowtime, which was programmed for the lower temperature. For temperatures above the upper pro-
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