Theory Of Operation - Horizon Fitness P-1000 Installation Instructions Manual

THEORY OF OPERATION

The P-1000 operates by timing the alternating electrical signals
generated by an operating magneto, see Figure 2, and mage
available on the magneto's "P" or grounding leads.
reciprocating engine aircraft have two magnetos on each engine
thousands of volts used to create sparks at the spark plugs.
RPM is derived from the repetition rate of the signals received from
the magnetos, and not the amplitude or shape of these signals. This
rate corresponds to the firing of the engine's spark plugs, and thus,
the turning of the engine.
The Microprocessor functions as two internal tachometers. It has the
ability to compare and store the RPM of each tachometer.
A difference of RPM reported from the two magnetos of the same
engine indicates that one of the magnetos may be failing (i.e. Mis-firing, severe fouling, sticking or floating points, etc.).
The RPM displayed on the LCD is the average of the right and left tachometer's RPM. Thus, if either tachometer begins to fluctuate or act
erratically, due to failure in its ignition system, the error will show in the display. Mechanisms are provided to mask these erroneous RPM
values and allow operation from the signal of the functional magneto.
Loss of a signal from either magneto is detected by the corresponding internal tachometer and a signal status indicator is turned on to
indicate the error. Short term (<½ second) differences between the right and left tachometers are also indicated to the pilot with a yellow
status indicator.
HORIZON INSTRUMENTS, INC.
Because
(See Figure 3), the P-1000
provides two terminals
connection to these "P" leads of
the right and left magnetos of the
engine. These "P" lead signals
are generally only a few hundred
volts as compared to
secondary output of the magneto,
which may generate tens of
P-1000 INSTALLATION & INSTRUCTION MANUAL
Title:
for
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Number:
P103050 E
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