TACHOMETERS
To meet the need of accurately measuring
the speed of rotating equipment, a large variety of sensors,
indicators and controls have been created: each combination
providing the best, or least expensive( or both), solution
for a specific application.
To that end, Marine and Industrial quality
tachometers are either hand-held or continuous operation,
and either mechanical or electrical/electronic. Direct coupled
mechanical tachometers for continuous RPM measurement are
becoming extremely rare, as the electrical/electronic types
are comparatively inexpensive and much more versatile. However,
some mechanicals are still available.
Hand Tachometer
- Contact
Contact types are available with analog dials or, as is
more common, with LCD or LED displays. The LCD type of display
is preferred due to battery life; the LED version is best
for poorly lit operations. Extreme care must be taken when
making measurements with contact tachometers; the rotating
device should be stopped, the contact tachometer placed,
and the rotations slowly brought up to speed.
The above are available with Cone
and Funnel Adapters as well as 6" and 12" circumference
measuring wheels.
- Non-Contact
The most popular non-contact type of hand tachometer is
the phototach. The instrument operates by directing a collimated
light beam onto a reflective marker attached to the rotating
object and the reflections received back by the instrument
are compared to an internal crystal time base for extremely
accurate measurements.
Another popular device is the strobe
tach, which flashes a light. When the light flashes enough
so that the rotating device appears to be stopped, rotational
(RPM) or reciprocating (strokes per minute) speeds can
be measured with precision.
In-Line Tachometer Sensors
and Readouts
Depending upon the need for forward-reverse
indication, slow speed operation, SAE Screw Drive connection,
and other factors, we can recommend a variety of sensors and
corresponding analog or digital meters, with repeaters, high
and low setpoint relay outputs, 4-20 mA or RS422 outputs etc.
as desired.
For Forward-Reverse indication, we can
offer a DC voltage Generator, such as the Westcon 750-type
A or J2, which put out 6 Volt DC per 1000 RPM. This is then
coupled with either an analog meter scaled in RPM and made
into a -DC voltage to 0 to + DC voltage meter to match the
generator. The other popular option is to utilize an encoder,
which utilizes a disc and photo-eye setup and provides + or
- pulses, which we then put into a digital rate counter and
calibrate to read in RPM or feet per minute or in whatever
engineering units are desired. Analog meters are possible
if the pulses are first run through a frequency to DC converter.
This adds, of course, significant cost and one more item to
the equation.
For slow speed, the encoder or the DC
tach generator are possible choices. Also, a special slow
speed magnetic pickup and magnet disc or shaft wrap or magnetic
strip with holes in it, is available as another possibility.
For +100 RPM, a key-way or a gear can
provide the pulses necessary for magnetic pickup. These pulses
can be read directly and economically in a digital rate meter
that we can scale in engineering units.
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