Taking Measurements - Extech Instruments RPM33-NIST User Manual

Taking Measurements
Non‐Contact (Photo) Tachometer Measurements
1. Prepare for the Non‐Contact measurement as described in the Measurement Preparation
section above.
2. Use the MODE button (momentarily presses) to select RPM (rotations per minute) or Hz
(Hertz: rotations per second) as the unit of measure.
3. Press and hold the MEASURE button to begin a measurement session. Hold the MEASURE
button down for the duration of the test and release it to end the session.
4. Point the meter toward the device under test at a distance of 2" to 20" (50 to 500mm). Be
sure to align the laser light beam with the reflective tape (see diagram above in previous
section).
5. Verify that the ( ( ( ) ) ) monitor indicator appears on the LCD when the reflective tape passes
through the light beam.
6. Read the measurement result from the LCD display.
7. When the MEASURE button is released the last reading will remain on the display for 5 to 10
seconds before the 'Auto Power OFF' feature switches the meter OFF. The HOLD display icon
will switch ON.
Non‐Contact (Photo tachometer) Measurement Considerations
 Bright ambient light may interfere with the reflected light beam. Shading the target area
may be necessary in some cases.
 The non‐reflective area must always be larger than the reflective area.
 If the shaft or rotating object is normally reflective, it must be covered with black tape or
paint before the reflective tape is applied.
 To improve repeatability of low RPM measurements, apply additional squares of
reflective tape. Divide the reading shown on the display by the number of pieces of
reflective tape squares to calculate the actual RPM.
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