tachometer problems
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Tachometer Problems

My analyzer is having trouble getting a tachometer reading


Possible causes & solutions

#1:  Cables may be disconnected or damaged

Your balancer may not be receiving signals from the tachometer because the cables are damaged or disconnected.  Check your cables to make sure they are properly connected and are not damaged.

#2 Damaged or missing reflective tape

Damaged reflective tape will not properly reflect the tachometer signal back to indicate full rotation. You may be receiving an erratic tachometer signal because the damaged tape reflects irregularly. On high RPM propellers the tape may be pulled off the propeller by aerodynamics. If this occurs you may secure the edges with clear fingernail polish. Ensure minimal amounts of polish are used and that the polish does not cover the reflective tape. Only the edges of the tape should be covered with the polish.

#3:  Misaligned Phototach

reflective tape alignmentYou should also check the alignment between the Phototach/LaseTach and the reflective tape.
To align the tachometer, rotate the propeller by hand until one blade is directly in front of the tachometer sensor. Apply power to the tachometer. Using a 2-inch-long piece of reflective tape with the backing paper still on, find where the tachometer sensor’s red beam is striking the propeller blade. The gate light on the back of the tachometer sensor will flash when the tachometer sensor “sees” the reflective tape.

An inspection mirror will help in viewing the back of the Phototach. If possible you can also look along the top of the Phototach and align the tape using the top of the Phototach as a “sight”. If the gate light cannot be seen outside in the daylight, you may see better results inside a hanger. A shadowed area is best when aligning the Phototach and reflective tape. If the gate light cannot be seen inside the hanger, the batteries may be losing their charge. Change the batteries and then align the reflective tape and Phototach. Attach the tape to the middle of the chord of the blade and at the vertical position of the blade where the light strikes. The picture below shows a properly installed and aligned Phototach and reflective tape.

reflective tape
Click to open larger version of this graphic.

When installing your reflective tape, you should make sure you use an adequate tape width. On the chart to the right, the left column gives propeller RPMs and the top row gives the minimum tape width requirement. The remaining figures are distance measurement.

Prior to using the chart, you need to measure the distance from the center of the propeller hub to your reflective tape.

To use the chart, locate the RPM at which your propeller rotates. Move to the right, locate the measurement on the chart that is higher than the measurement you made on the propeller. If you measurement is not shown on the chart, you should locate the measurement that is within your RPM but is the next highest measurement. Move up the column to the tape width requirements. The number at the top of the column is the required minimum tape width for the RPM and distance form the propeller hub you are using.

To install wider tape widths, use multiple 2-inch-long pieces of reflective tape placed side by side.


 

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