4
Magtrol Hysteresis Dynamometers
Chapter 1 – Introduction
GENERAL
INFORMA
TION
2
MAGTROL
HD / ED
Principles and Selection
operating principles
AIR GAP
FIELD COIL
BALL BEARINGS
SHAFT
POLE STRUCTURE
HUB
ROTOR
(Drag Cup)
Magtrol Hysteresis Dynamometers absorb power with a
unique Hysteresis Braking System which provides frictionless
torque loading independent of shaft speed. The Hysteresis
Brake provides torque by the use of two basic components—a
reticulated pole structure and a specialty steel rotor/shaft
assembly—fitted together but not in physical contact. Until
the pole structure is energized, the drag cup can spin freely
on its shaft bearings. When a magnetizing force from the
field coil is applied to the pole structure, the air gap becomes
a flux field and the rotor is magnetically restrained, providing
a braking action between the pole structure and rotor.
complete pc control
Magtrol’s M-TEST 7 Software is a state-of-the-art motor testing
program for Windows®-based data acquisition. Used with
a Magtrol Programmable Dynamometer Controller, Magtrol
M-TEST 7 Software provides the control of any Magtrol
Dynamometer and runs test sequences in a manner best suited
to the overall accuracy and efficiency of the Magtrol Motor Test
System. The data that is generated by Magtrol’s Motor Testing
Software can be stored, displayed and printed in tabular or graphic
formats, and can be easily imported into a spreadsheet.
Written in LabVIEW™, M-TEST 7 has the flexibility to test
a majority of motor types in a variety of ways. Because of
LabVIEW’s versatility, obtaining data from other sources (e.g.
thermocouples), controlling motor power and providing audio/
visual indicators is relatively easy.
Magtrol’s M-TEST 7 Software is ideal for simulating loads,
cycling the unit under test and motor ramping. Because it is
easy to gather data and duplicate tests, the software is ideal for
use in engineering labs. Tests can be programmed to run on
their own and saved for future use allowing for valuable time
savings in production testing and incoming/outgoing inspection.
Dynamometer selection
Magtrol’s Hysteresis Dynamometers cover a wide range of
Torque, Speed and Mechanical Power ratings. To select the
appropriate size Dynamometer for your motor testing needs,
you will need to determine the
Maximum Torque, Speed
and Power
applied to the Dynamometer.
Maximum Torque
The Magtrol Hysteresis Absorption Dynamometer will
develop braking torque at any speed point, including low speed
and stall conditions (“0” rpm). It is important to consider
all torque points that are to be tested, not only rated torque,
but also locked rotor and breakdown torque. Dynamometer
selection should initially be based on the maximum torque
requirement, subject to determining the maximum power
requirements.
Maximum Speed
This rating is to be considered independent of torque and
power requirements, and is the maximum speed at which
the Dynamometer can be safely run under free-run or lightly
loaded conditions. It is not to be considered as the maximum
speed at which full braking torque can be applied.
Maximum Power Ratings
These ratings represent the maximum capability of the
Dynamometer Braking System to absorb and dissipate heat
generated when applying a braking load to the motor under
test. The power absorbed and the heat generated by the
Dynamometer is a function of the Torque (T) applied to the
motor under test, and the resulting Speed (n) of the motor.
This is expressed in these power (P) formulas:
The Dynamometer’s ability to dissipate heat is a function of
how long a load will be applied. For this reason, the maximum
power ratings given are based on continuous operation under
load, as well as a maximum of 5 minutes under load.
To safely dissipate heat and avoid Dynamometer failure, the
maximum power rating is the most important consideration
in selecting a Dynamometer.
SI:
P (watts) = T (N·m) × n (rpm) × (1.047 × 10
-1
)
English: P (watts) = T (lb·in) × n (rpm) × (1.183 × 10
-2
)
Metric: P (watts) = T (kg·cm) × n (rpm) × (1.027 × 10
-2
)
All of Magtrol’s controllers, readouts and software
calculate horsepower as defined by 1 hp = 550 lb·ft / s.
Using this definition:
hp = P (watts) / 745.7
HD / ED
Magtrol offers three types of dynamometer brakes to absorb load: Hysteresis, Eddy Current and Magnetic Powder. Each type
of Dynamometer has advantages and limitations and choosing the correct one will depend largely on the type of testing to be
performed. With over 50 models to choose from, Magtrol Sales professionals are readily available to assist in selecting the proper
Dynamometer to meet your testing needs.
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