Magneto P-Lead Tachometer Signal Stabilizer (P-TACH)

The P-TACH converts the electrically noisy and variable magneto P-Lead signal from aircraft magnetos into a stable digital pulse waveform for processing by modern digital engine monitoring systems.

The P-TACH eliminates spurious over-or-under-indication of rpm readings by filtering and stabilizing the variable magneto impulses.  A typical magneto impulse is shown in the picture below.  Variation of the magneto impulses occur due to changes in rpm, spark plug gapping, ignition wire condition and age.  In multi-cylinder engines, magneto pulses vary between cylinders, making it difficult for simple tachometer circuits to operate reliably.

The P-TACH is mounted on either side of the firewall where it is not subject to the high temperatures and vibration that cause engine-mounted sensors to fail.  Due to its compact size, it may be secured simply by tie-wrapping onto an existing wiring harness as shown in below.  Only four wires are required- sensor power, ground, p-lead input and tach output.

Download the installation manual here.

All of the P-TACH circuitry is mounted in a 15-pin D-subminiature connector shell.   There is a single threshold control that is factory-set to 50% and will work in most applications.  If unreliable RPM indications are noticed, small adjustments may be made with a screwdriver.  Note that one P-TACH per magneto is normally installed.  So if you have two magnetos, two P-TACHs would be required.

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