Commtest Instruments vbBalancer Instrument Reference Manual page 41

Setting up the tachometer
Locate the drill hole in the tachometer and screw this onto
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the end of the mounting base movable arm.
Plug the cable socket into the tachometer connecting pins
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then turn the locking ring to make a secure connection.
Locate the TACH input on the instrument and attach the
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other end of the cable to this.
Stop the rotor.
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Cut out a small strip of the supplied reflective tape,
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approximately 5 mm x 15 mm (0.2" x 0.5").
Stick the reflective tape to a machine part that rotates at the
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rotor speed e.g. the shaft. This trigger spot should provide a
pronounced increase in reflection as it passes under the
tachometer light beam. The tape width must be at least
double the diameter of the light beam spot.
Mount the tachometer magnetic base to a stationary portion
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of the machine, convenient to the trigger spot.
Position the tachometer slightly away from the centerline of
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the rotating machine part in order that it is not 'blinded' by
reflections from the surface of the machine part. The sensor
should be positioned within the measurement range shown
in the following diagram.
Start the rotor and wait till it is at normal running speed.
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Section 3: Using Sensors 33