Extech Instruments 461830 User Manual page 5

Important Note on Test Durations
The Xenon lamp has test time restrictions. If the specified test durations and cool-down period are
not observed, damage to the instrument can result and the life of the lamp can be shortened.
Range
< 3000 RPM
> 3000 RPM
Notes on Speed Measurements
Ensure that the mark, or reflective tape, is providing a 1:1 measurement. Check that there is only
one stationary mark and not two, four, or more, on the object under test.
Two or more stopped marks indicate a 'harmonic' measurement (2:1, 3:1, 4:1 etc.) and the
instrument will display double, triple, or quadruple the actual speed. A useful method of avoiding
harmonic measurements is to adjust the FINE/COARSE knobs until two images (marks) appear and
then lower the flash rate (via FINE/COARSE knobs) until a single, stationary image appears. This
will be the actual speed.
In the example below, a rotating shaft is affixed with one piece of tape. The illustrations represent
five possible scenarios.
If more than one mark appears, the image is showing a 'harmonic'. The bold column (1000/1000
rpm), below, shows the actual speed of the shaft. The 1000/500 rpm column indicates a harmonic,
whereby the actual speed is divided in half. To avoid this, adjust the 'FINE' and 'COARSE' knobs
until you see the 'doubled harmonic' (1000/2000 rpm column), then the 'halved harmonic' (1000/500
rpm column), and then the actual speed (bold column 1000/1000 rpm).
Shaft speed
Strobe flash rate
Visible marks
The display has an AUTO RANGE INDICATOR (flashing decimal at the far right) that appears
when the readings are > 10,000 RPM. In these cases, multiply the displayed reading by 10.
Maximum Test Duration
Thirty (30) minutes
Five (5) minutes
1000rpm 1000rpm
500rpm 1000rpm
1 1
1000rpm 1000rpm
2000rpm 3000rpm
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Cool-Down Period
Ten (10) minutes
1000rpm
4000rpm
3 4