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|  MIL-T-26219A
3.9.1 Control knobs.
Each rotary-type switch shown on Figure 2 shall be
furnished with a one-piece molded General Radio Type KNB-1 knob, or equal,
black in color, and provided with a bored brass insert and bushing for a
1/4-inch shaft utilizing two set screw 90 apart. The knob shall incorporate
a bar type extension to facilitate switching operations.
The pointer shall be
provided with a white reference marking.
The control knob provided for
controlling the variable speed drive shall be of suitable size, configuration
and design to permit rapid and precise setting of the output speed of the test
set by operating personnel over the complete design range. The knob shall
incorporate an auxiliary spinner.
3.10 Variable speed drive. The variable speed drive shall consist of a
electric motor, associated gearing, controls, and a means for providing
signals to drive the precision rotational speed indicator.
3.10.1 Variable speed drive control. The drive shall be designed to be
infinitely variable in output speed over the complete range from O to 5000
revolutions per minute. The design shall be capable of adequately
transmitting the horsepower produced by the motor and as dictated by the
overall load requirements of the test set. The torque required to change the
output speed of the drive during operation by means of the control shaft shall
not be less than 3 nor more than 6 inch-ounces. When the test set is not in
operation, the drive shall not be damaged in the event the control knob is
rotated. The design shall be trouble free and suitable for continuous duty
usage.
It shall be quiet running and capable of providing a high degree of
stability.
3.10.2 Motor.
The electric motor required for driving the variable speed
20
drive shall be designed to operate directly from a single phase, 400
volt A-C power source or through a metallic rectifier power
cycle, 115
unit. The motor shall be suitable for continuous duty usage. It shall be
capable of producing the horsepower required by the tester for fulfilling the
tests specified in section 4.
During accomplishment of applicable tests, the
temperature rise of the motor shall be maintained within a limit which shall
not adversely affect the performance characteristics of the test set. It
shall be equipped with an enclosure capable of adequately protecting the
operation parts and windings. The enclosure shall be designed to mount on the
housing provided for variable speed transmission. The bearings shall be of
the ball-bearing type and shall be grease-packed.
3.10.2.1 Power supply switch. The electric motor shall be electrically
energized and de-energized by means of a double pole toggle switch conforming
to AN3027-9. Overload protection shall be provided between the input
electrical connector receptacle and the power switch.
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