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Dimensions (LxWxH):6.13” x 3.25” x 1.75 “ plus 4.75” handle
[155.7 mm x 82.6 mm x 44.5 mm x 120.7 mm]
Weight: 1.25 lbs [0.57 kg]
OVERVIEW
The HHT21A SERIES combines the accuracy and safety of a non-contact
optical tachometer with the convenience and ease of operation of a pistol
grip instrument. The instrument provides non-contact measurement of
rotational speed to an accuracy of .01% of reading. It reads RPM directly to
the nearest RPM, and a ‘on-target’ indicator is provided to verify the
instrument is properly aligned on a target and receiving valid information.
OPERATION
The HHT21A measures rotational speed from a single pulse per revolution.
This pulse is supplied by marking the rotating shaft with a visible reflective
tape target. The HHT21A is equipped with a built-in laser light source
providing a bright red beam which is aimed at the reflective tape located on
the rotating shaft. The pulse from the reflective tape is received back
through a single lens reflex optical system and detected by a photocell
inside the instrument. The HHT21A then computes the rotational speed
and displays it to a resolution of 1 RPM.
To operate the instrument, simply aim it at the reflective tape while holding
it at a distance of 1 inch [25.4 mm] to 10 feet [3.1 m] making sure to observe
laser safety precautions. Squeeze the pistol grip trigger, and read the indicated
speed. The on-target indicator must be on. The display is updated up to
twice per second.
For longer duration measurements, the trigger latch on the side of the pistol
grip handle can be depressed after pulling the trigger, and the instrument
may be mounted on the 1/4-20 threaded bushing at the base of the handle.
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When the trigger is released, the HHT21A will hold the last measurement
taken and display it for up 90 seconds.
On very small shafts, the HHT21A will work down to a reflective tape size
of approximately 1/8 inch [3.2 mm] square. However, with this small tape
size, it would be necessary to operate the instrument very close to the
rotating shaft and insure it is held steady. For normal operation, a tape size
of approximately 1/2 inch [12.7 mm] square or larger is recommended, and
on very large diameter shafts or for very high-speed applications, a larger
size piece of tape may be required. It is also recommended that the reflective
tape be viewed just slightly off the perpendicular. The HHT21A will
operate at angles from 0 to 45 degrees, but best results are obtained by
aiming the instrument at the reflective tape at approximately a 10 to 20
degree angle. This insures that only pulses from the reflective tape are
received by the instrument and minimizes the problem of interference from
a highly polished surface or varying ambient lighting.
USING THE HHT21A-R WITH A REMOTE OPTICAL SENSOR
The HHT21A-R version of the tachometer has a provision for using the
optional HHT20-ROS Remote Optical Sensor. In addition to the standard
built-in optics of the HHT21A SERIES, a 1/8 inch [3.5 mm] phone jack is
provided on the front panel of the Tachometer to accept a remote optical
sensor plug. A toggle switch on the optics panel selects internal or remote
operation.
For applications requiring the remote optical sensor, move the Remote/
Internal switch to the remote position to disable the internal optics of the
Tachometer. When the trigger is pulled or latched, the remote optical sensor
can be used for measurements. The HHT20-ROS Remote Optical Sensor
operates 3 feet [0.9 m] and ±45° from the reflective tape.