Technical data are subject to change without notice.
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SPM Instrument AB • Box 504 • S-645 25 Strängnäs • Sweden
Tel +46 152 225 00 • Fax +46 152 15075 • info@spminstrument.se • www.spminstrument.se
Measuring speed
To evaluate bearing condition and to make sense of a vibration spectrum, you have to know the
rpm of the shaft. The RPM menu turns up as soon as the speed probe is connected to the EXT
connector.
Easiest is the optical speed measurement. The preparations are simple: you paste a bit of adhesive
reflecting tape on the rotating part. It has to be reasonably clean.
Direct the light beam at the reflecting tape. Press and hold down the M key until the result is
displayed. The instrument counts 1 rpm for each received light reflex. The minimum is one count
every 6 seconds (corresponding to 10 rpm). On slowly rotating parts you can use several reflexes at
even intervals, and divide the displayed value by the number of tape bits to get the rpm.
For contact measurement, you place the contact adapter over the lens and fix a contact center or a
wheel. The adapter has a reflecting tape inside, and each revolution sends one light reflex to the
counter. The contact center is pressed firmly into the cavity at the center of the shaft, and the
probe is aligned with the shaft's center line. The wheels are used to measure peripheral speed.
One turn corresponds to 0.1 m, 0.1 yards, or 0.5 feet, depending on the wheel type. For meters or
yards per minute, divide the displayed result by 10. For feet per minute, divide by 2.
The display cannot be zeroed. If you want to clear a reading before measuring again, hold the
contact adapter over the lens, hold down the M key and turn the adapter shaft so that the peak
indicator blinks once. Wait until the display shows <10 rpm, then release the M key.
RPM
3650 rpm
Speed reading
RPM, optical:
Distance max. 0.6 m
Reflecting
tape
RPM, contact center:
Hold against shaft center
Peripheral, contact wheel:
Multiply reading by wheel factor
TAD-12 0.1 m/min.
TAD-13 0.1 yd./min.
TAD-17 0.5 ft./min.
Measuring speed 51
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