devices give such long, trouble-free performance as
Models 120 Tachometers. Many have been in daily service
for over twenty years with little maintenance of any
In terms of long term
accuracy, linearity, and ease of calibration, Models
120 tachometers have no peers. Their interference-free
dc system makes shielded cable unnecessary so long
to withstand difficult environments (chemicals, water,
etc.) runs are possible at low cost with conventional
wiring techniques. While magnetos operate reliably
at armature shaft speeds up to 5,000 RPM, it should
be noted that their performance at low speeds far
exceeds that of photocells, magnetic pickups and other
The magnetos, digital
& analog (dial) indicators, and accessories cover
most industrial requirements. However, many modifications
are regularly engineered for specific applications.
The Type M-1200 B Magneto is the most popular. The
choice of indicators depends largely on personal preference
as to type of readout, physical size, scale length
or readability, and possibly the need for illumination
and explosion-proof or water-tight cases.
All M-1200 Magnetos have
the same internal construction and electrical characteristics.
They differ only in mounting arrangements, speed requirements,
and methods of coupling to the speed source (via spur
gearing, couplings, friction wheels, etc.). Each magneto
generates a dc voltage exactly proportional to speed.
It electrically connects to from one to ten analog
or digital indicators calibrated in any desired speed
function such as RPM, feet per second, units per hour,
etc. Magnetos also readily adapt to process control
Wherever possible, the
magneto should be geared so that its armature speed
is at least 200 RPM for full scale reading on standard
indicators; at least 20 RPM for full scale with highly
damped indicators. Models with integral gearboxes
allow for input shaft speeds for full scale reading
that are as high as 30,000 RPM, or as low as ½
RPM. Although the required drive is always based on
the speed the armature turns for full scale on the
indicator, the indicator will be accurate over the
entire range from zero to full scale. Thus with a
½ RPM input shaft speed for full scale, an
indicator marked 0 to 50 Inches Per Minute will read
properly at 1 IPM even though the input shaft only
turns at .01 RPM for this reading.
For longest life under
continuous running conditions, armature speed should
be kept under 2000 RPM although the magnetos give
excellent service at speeds up to 5000 RPM.
M-1200 magnetos are individually
run-in and aged to insure long term stability, neutralized
to generate the same voltage for either rotation,
and adjusted with a magnetic shunt to generate a standard
voltage for easy interchangeability.