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6.0 General Description
The photo tachometer consists of the coaxial photo tach head, reflective tape and built-in
connecting cable.
RPM is displayed in the right hand side of the digital display when TACH is selected on the
rotary switch. Pressing the units button switches to RPM or RPM/N. RPM assumes the
sensor provides one pulse per revolution of the shaft. RPM/N assumes the sensor provides
N pulses per revolution of the shaft. The value of N can be varied (See section on
programming) the tester.
6.1
Photo Tach Head
The Photo Tach Head senses the speed of a rotating body without physical contact.
Its design permits it to be used over a wide range of distances from the rotating body.
When reflected light is detected by the photo tachometer a red 'on target' LED
indicator illuminates to confirm alignment. Accessories include a flex arm and
magnetic base. These can be used in various combinations to mount the Photo Tach
Head. The Unit has a built-in cable to connect the tach head to the tester.
7.0 Object Preparation
The Photo Tach Head will only sense the change in reflected light from a moving object.
Therefore, a rotating shaft with a uniform reflective surface must be marked with pieces of
reflective tape supplied with the photo-tachometer. Select a convenient position on the
shaft, pulley or coupling which has a minimum diameter of 35 mm (1.4 inches). Larger
diameter shafts will give better results, particularly at high speeds. The surface should be
preferably free from bolt holes, keyways etc. Clean the surface and fix a piece of reflective
tape, approximately 20 mm (0.8 inches) long. If this does not give sufficient contrast it may
be necessary to paint or cover the remainder of the shaft with matt black or use larger
pieces of reflective tape.
For shaft speeds lower than 800 rpm use 2 pieces of reflective tape, and program the
"TACH" channel with a factor of 2.
7.1
Obtaining a Reading
Connect the cable in the Tach Head and attach the magnetic base. Fix the magnetic
base in a suitable position and aim the light at the rotating object. Switch on the tester,
select TACH and position the Photo Tach Head 150 mm (6 inches) away from the
object and read the r.p.m. directly on the meter. If no reading is obtained move the
head closer to the shaft. If the reading is fluctuating select slow update and increase
the distance from the shaft until a steady reading is obtained. The distance of the
Photo Tach Head from the object will vary depending on the ambient lighting, size of
the object, amount of contrast and the speed of the object. Certain types of ambient
lighting may require shading of the rotating object or applying a larger reflective mark
will correct the situation.
Note: Infrared light is NOT visible to the naked eye.
Photo Tachometer
12
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