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|  MIL-T-26219A
3.11.1 Electronic components. The rotational speed indicating system
shall incorporate a minimum number of electronic components including vacuum
tubes.
All the components shall be operated at conservative levels. The
circuits shall be so designed that the aging of the vacuum tubes will not
adversely affect the accuracy of the indicating system. The system shall be
capable of monitoring the ouput speed of the variable drive and of increasing
or decreasing automatically and consecutively with like changes in the output
speed of the variable drive.
Transistors shall be employed in the circuits in
lieu of vacuum tubes wherever practicable.
3.11.2 Display. An in-line type display consisting of not more than 5 nor
less than 4 digits shall be provided as shown on Figure 2. The display shall
be designed to indicate in rpm multiplied by 1, rpm multiplied by 2 and
percent rpm depending upon the setting of the "RPM-PERCENT RPM" switch located
on the panel.
In lieu of the selector switch approach specified, the display
may incorporate individual digital indications of percent rpm, rpm x 1, and
rpm x 2 which function simultaneously and do not require a selector switch.
Ranges from O to 5,000, 0 to 10,000 (9999) and O to 119.04 (119.0) shall apply
to the indications in rpm x 1, rpm x 2, and percent rpm, as applicable to the
4- or 5- digit displays. When the indicator is set to indicate in percent rpm
a decimal point shall register between the third and fourth digits reading
from left to right. Unless otherwise approved, the display shall incorporate
neon gas discharge type tubes or drum type counter wheels.
The basic design
selected shall be capable of displaying digits 0-9 in any selected order as
controlled by the associated switching circuits. The basic size of the
numerals shall not be less than 0.187 inch or more than 0.5 inch in height.
3.11.3 Fuse.
The rotational speed indicating system shall be designed to
10V 400
20 cycle, single-phase power source.
operate from a 115
The input
power circuit to the indicating system shall be protected with a suitable fuse
which shall be contained within a holder mounted on the panel.
The fuse shall
be replaceable from the front of the panel.
3.11.4 Accuracy. The rotational speed indicating system shall be capable
10.0 rpm,
20.0 rpm, and + 0.2
of providing measurement accuracies of
percent rpm respectively for the rpm x 1, rpm x 2, and percent rpm indicating
ranges.
3.12 Voltmeter.
An alternating current voltmeter conforming to
MIL-M-10304, as applicable, shall be provided on the control panel as shown on
Figure 2. The indicating range shall be O to 30V. The design shall be
suitable for measuring three phase alternating current voltage generated by
two pole and four pole aircraft tachometer generators wherein the frequency
may vary over a range of 10 to 70 cycles per second. The scale length shall
be a minimum of 2 inches.
The case shall be of the 3-1/2 inch size. An
accuracy of
2 percent shall apply.
The resistance of the meter shall be
such that it does not draw sufficient current to unbalance the resistance load
during the accomplishment of tachometer generator output voltage tests.
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