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RPM-8000-PRO offers a discerning solution for
automotive RPM measurement without an additional sensor: the practical
instrument is simply connected via a standard jack to the cigarette
lighter socket and the RPM is shown directly on the LCD display. You even
have the choice to output the data as an analog voltage (1 Volt per 1000
rev/min) or as a digital pulse sequence (TTL). The smart measuring
principle is based on an analysis of the ripple balance of the supply
system, characteristic for all automotive alternators. The frequency of
this ripple amounts to about 100 to 120 pulses per engine rotation and
therefore delivers good dynamic measuring results.
Though the frequency is proportional to the
engine RPM, it also depends on the gear transmission ratio from crankshaft/alternators
and on the number of alternators poles and phases. This makes the
calibration of the input signal to the actual measured RPM necessary. The
latest version of the RPM-8000-PRO now offers two elegant options:
• Internal calibration: The internal
calibration assumes a steady engine RPM of 2000 rev/min, which can be
monitored by the automotive tachometer. By pushing the “Cal. Int” button
the calibration starts, whereby the instrument assigns the actual measured
pulse frequency to speed “2000” and outputs the actual engine RPM to the
LCD display.
• External calibration (option): A laser
RPM ”RPM-LASER-CAL” is needed for this option. A reflector tag is mounted
on the crankshaft and scanned by laser beam. The TTL output of the laser
instrument is connected via cable to the “Ext. Cal In.” input of the
RPM-8000-PRO and delivers one pulse per rotation. By comparing the pulse
sequence with the measured pulse frequency, the instrument calculates
automatically the relationship between ripple balance and speed. Identical
displays on laser and RPM-8000-PRO signal successful calibration (also
shown by luminescent LED’s).
The measuring range of the analog output
can be varied on demand via jumpers (e.g. to 0.5, 1.0 or 2.0 Volt per 1000
rev/min). The TTL output can also be scaled with a frequency factor of 1:8
or 1:16 – and therefore adapted to the resolution ability of attached
measuring systems. For testing purposes this “factor” between speed and
TTL frequency can be output, instead of the speed, to the LCD display by
pushing the “TTL” button. The instrument saves the calculated calibration
data in non-volatile memory until the next calibration.
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