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User's Guide
Mini Photo Tachometer Model 461700
Mini Contact Tachometer Model 461750
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Page 2
Introduction
Congratulations on your purchase of the Extech Tachometer.
The Model 461700 Photo Tachometer uses precision optics and reflective tape to
measure the RPM of rotating devices such as fans and gears.
The Model 461750 Contact Tachometer uses convex and concave attachments to
measure RPM. It also has a built-in wheel to measure the linear surface speed of moving
devices such as conveyors and treadmills. Careful use of this tachometer will provide
years of reliable service.
Specifications
General Specifications
Display 5-digit LCD Display
Range selection Automatic range selection
Time Base 4MHz Quartz Crystal
Sampling Time 1 second (>60 rpm); >1 second (10 to 60 rpm)
Photo Tachometer Distance 2 to 12” (5 to 30cm)
Operating Temperature 32 to 122oF (0 to 50oC)
Operating Humidity 80% RH Max.
Power supply 9V Battery
Battery Life 40 hours (approx.)
Applicable standards EN 50081-1/1992 (EN 55022)
EN 50082-1/1997 (EN 55024)
Dimensions 461700: 4.9 x 2.0 x 1.3” (124 x 51 x 33mm)
461750: 5.9 x 2.0 x 1.3” (150 x 51 x 33mm)
Weight 461700: 4.0 oz. (114g); 461750: 5.0 oz. (142g)
Range Specifications
Measurement Range Accuracy
Rotation
(461700 Photo)
Rotation
(461750 Contact)
Surface Speed
(461750)
10.000 to 99999 rpm ± (0.1% reading + 2 digits)
10.000 to 9999 rpm ± (0.1% reading + 2 digits)
3.0000 to 6560.0 ft/min
1.0000 to 1999.9 m/min
1.0000 to 5000.0 yds/min
± (1.5% reading + 2digits)
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Meter Description
Display Description
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461750 Safety Precautions
The 461750 incorporates a finger guard for protection. However, care should be taken
when measuring surface speed to avoid injury.
1. Hold the meter firmly when touching the wheel or attachment to a moving object
2. Keep fingers behind the finger guard while taking measurements
3. Keep your eyes and attention on the measurement activity at all times
4. Do not attempt to record measurements while holding the meter to the moving object
(use the Data Hold feature to freeze the reading on the LCD; refer to the Data Hold
section of this manual).
Meter Power
Power ON / OFF
1. Press the triangular POWER HOLD button to turn the device ON. Alternatively, press
the button at the bottom of the meter (just under the LCD) which doubles as a power
on/off button. Two buttons are provided for easy reach at any holding angle.
2. Press and hold the triangular POWER HOLD button (or the alternate button) for
approx. 5 seconds to turn the device OFF.
Auto Power OFF
1. The meter turns off AUTOMATICALLY after 20 minutes.
2. For 461750 only: To disable this feature, turn the meter off. Then press and hold the
POWER and UNITS buttons until the meter turns on. Release the POWER button first
and the ‘n’ display icon will appear. This indicates that the feature is disabled.
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Measurements
RPM Measurements
461700 Photo Tachometer
1. Affix a small (1/4”) square of reflective tape to the surface of the device under test.
See rotating gear example diagram below.
2. Allow the device under test to turn at its normal rate.
3. Turn the meter ON.
4. Point the Tachometer’s sensor toward the reflective tape. Keep the sensor
perpendicular to the reflective tape for the best results. The distance from meter to
object can be up to 12” (30cm).
5. Read the RPM (rotations per minute) measurement on the LCD.
Reflective Tape: Point
meter sensor toward tape
Rotating Gear
Front view
461750 Contact Tachometer
1. Affix the convex (cone) or concave (funnel) attachment that best fits the application
to the meter shaft as shown below.
2. Turn the meter ON.
3. Use the UNITS button to select RPM (the display will reflect the selection).
4. Touch the attachment to the moving object and read the displayed measurement.
Rotating
Wheel
Touch the convex or
concave attachment
to the turning object
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Surface Speed Measurements (461750 only)
1. Turn the meter on as described previously.
2. Touch the wheel to the moving object and read the measurement on the display. Refer
to diagram below.
3. Use the UNITS button to select the unit of measure: ft/min (feet per minute); m/min
(meters per minute); yds/min (yards per minute).
Conveyor
belt
Data Hold Feature
After the meter is turned on, the POWER-HOLD button can be pressed and released to
activate Data Hold. Data Hold automatically freezes the displayed reading. While the
reading is held, the HOLD display icon switches on. Press the POWER-HOLD button again
to exit this mode.
Touch wheel to moving belt
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