Operating Principles; Speed; Torque; Figure 5-1 Mechanical Layout Of A Load Cell - Magtrol HD-106 User Manual

5. Operating Principles

5.1

SPEED

Inside the dynamometer enclosure is an optical speed transducer. A high-speed optical switch,
consisting of an Infrared (IR) LED and IR receiver, senses the passage of light through a slotted disk
that is attached to the end of the dynamometer shaft. Light passing through a slot in the disk causes
the speed output signal to go to a logic low (near 0 VDC). As a solid section passes in front of the
IR receiver, the output signal switches to a logic high (near 5 VDC). Rotation of the disk results in
the optical switch generating a pulse frequency of 60 bits per shaft revolution. For schematic, see
Section B.2 – Speed Sensor Board in Appendix B.
5.2

TORQUE

Torsional force from the hysteresis brake assembly is measured by a load cell. The load cell consists
of a flexing beam with four strain gauges. The strain gauges are in a bridge configuration, producing
an analog signal proportional to torque.
The load cell schematic in Appendix B shows voltage levels and connection identifications. The
mechanical diagram below illustrates how the assembly clamps onto the rear support member of
the brake.
LOAD CELL PC BD.
TEMP COMP
PIVOT ASSEMBLY
STRAIN GAUGES
WIRE COLORS --
BLUE GREEN WHITE RED
Figure 5–1 Mechanical Layout of a Load Cell
52
FINE BALANCE
LOCKING SCREW
LOAD CELL
ASSEMBLY
NOTE: A coarse balancing
resistor, located on the
torque signal amplification
board, may be connected
between the blue or green
and white wire terminals.