5
Magtrol Dial Weight Dynamometers
User’s Manual
3.2.1
t
orque
s
Cale
G
raduations
Some torque scale graduations are more difficult to read (rapidly) than others. What usually works
well for most people, is to record torque data points from the easiest reading scale; then correct all
data to correspond to the particular range (counterweight) selected, by multiplying (or dividing) by
2 or 4.
3.3
POWER DISSIPATION
All Magtrol Dynamometers are power absorption instruments. As a dynamometer loads a test
motor, it is absorbs horsepower from the motor into the hysteresis brake. The brake then converts
this mechanical energy into heat.
There are finite limits to the amount of energy and resulting temperature rise that any absorption
brake can withstand. Rapidly rising operating temperatures from excessive power input can cause
severe mechanical distortion of the rotor assembly. This, in turn, may cause the rotating assembly
to contact the stationary members that surround it. Once this happens, metal transfer and ultimately
seizing of the brake assembly may occur.
Excessive power over extended periods of time may result in more obscure damage including
breakdown of bearing lubricants and degradation of magnetic coil insulation.
3.3.1
P
ower
a
BsorPtion
C
urves
The following graphs (
Figures 3–1 through 3–6
) represent the maximum power (heat) that
the dynamometer can dissipate over time. The specifications shown are conditional upon the
following:
• Maximum brake temperature = 100 °C (212 °F)
• Ambient temperature = 25±5 °C (77±9 °F)
The following torque/speed-to-horsepower conversion formulas are provided for your convenience.
They are sufficiently accurate (within 1%) to establish horsepower (hp) for use in the heat rise
curves.
hp = oz·in × rpm × 1.00
×
10
-6
hp = lb·ft × rpm × 1.90
×
10
-4
hp = oz·ft × rpm × 1.19
×
10
-5
hp = lb·in × rpm × 1.59
×
10
-5
hp = g·cm × rpm × 1.38
×
10
-8
hp = N·m × rpm × 1.40
×
10
-4
Note:
Please take a moment to familiarize yourself with any limitations
that may apply to your specific dynamometer and motor testing
requirements.