MIL-M-23167B(SHIPS)
3.3.10 Mounting. Frequency meters shall be mounted on a panel drilled in accordance with the appli- cable drilling plan, and shall be mounted by means of mounting bolts or studs (see figures 1 and 2). The necessary mounting bolts (screws), nuts and lockwashers shall be supplied with each meter.
3.4 Calibration.
3.4.1 Position. Frequency meters shall be calibrated in the position in which they are normally used, and shall meet the accuracy requirements specified herein in such position at the reference temperature. Normal position is defined as with the scale in a vertical plane.
3.4.2 Mounting panel. The Frequency Meters shall meet the accuracy requirements specified herein when mounted on a magnetic steel panel 1/8 inch thick.
3.5 Initial accuracy. The initial accuracy expressed as a percentage of center-scale and in absolute value shall be within the limits specified in 3.19 (see 4.3.4).
3.6 Harmonic content effect. The frequency meter shall not exceed the error specified in 3.19 when subjected to the test specified in 4.3.16.
3.7 Voltage range. Frequency meters shall operate over the range specified in 3.19 and the change in indication from the reading at nominal voltage shall not exceed the value specified (see 4.3.7).
3.8 On-off cycling. Meters shall withstand on-off cycling test specified in 4.3.8 without change in indication exceeding that specified in 3.19.
3.9 Overvoltage. Meters shall withstand the test of 4.3.9 without damage or permanent change in indication exceeding the value specified in 3.19.
3.10 External field influence. Frequency meters shall have sufficient magnetic shielding so that the effect of an external field of 5 oersteds will not cause a change in indication greater than the value specified in 3.19 (see 4.3.10).
3.11 Temperature range. Frequency meters shall indicate freely (see 6.5.3) during and after the test specified in 4.3.11. The permanent change in indication shall not exceed the values specified in 3.19.
3.12 Inclination. Frequency meters shall indicate freely (see 6.5.3) during the test specified in
4.3.6. The change in indication shall not exceed the value specified in 3.19.
3.13 Vibration. When tested in accordance with 4.3.14 no screws, bearings, pivots or other parts shall be so loosened or damaged as to cause a change in indication greater than the value specified in 3.19.
3.14 Shock (high-impact). When tested in accordance with 4.3.15 no screws, bearings, pivots, windows or other parts shall become loosened, cracked or unduly damaged. The permanent change in indication based on calibration made after resetting the pointer to zero shall not exceed the value specified in 3.19.
3.15 Dielectric stress. When tested in accordance with 4.3.12, frequency meters shall withstand a voltage of 2,600 volts a.c. without damage or flashover.
3.16 Insulation resistance. The insulation resistance of frequency meters shall be not less than
20 megohms (see 4.3.13).
3.17 Marking. Frequency meters shall be permanently and legibly marked with the applicable informa- tion specified in 3.17.1.
3.17.1 Dials. Dial markings shall be sharply defined and visible from the front of the case. These markings shall not however, be so conspicuous as to distract attention from the scale markings. The scale markings and numerals and items (a), (b), (c), and (d) shall be marked on the dial; items (a) through (h) shall be marked on the dial, on the front of the meter, or on an attached identification plate. Marking shall conform to MIL-STD-130.
(a) Designation of the quantity measured (Hertz).
(b) Nominal voltage rating (120, 450 and so forth as applicable). (c) Type designation (see 1.2.1).
(d) MIL-M-23167.
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