MIL-DTL-83729C
(b)
In the contact circuit, set the oscillator frequency between 20 kHz and 30 kHz.
(c)
Set R1 from 50,000 ohms to value required (see 3.1 and 6.2.2) for maximum contact current rating (S1
closed).
(d)
Set R2 for 3 ohms. Set the gain of pre-amp and scope to present an average vertical deflection of 8
centimeters.
(e)
Open S1, maintain a constant vertical deflection and adjust R2 until the voltage drop (V) across the contact is
1/5 to 1/10 R2 V drop.
(f)
The dynamic contact resistance is the calculated ratio of the contact V drop times the resistance R2 (Note:
Lead length must be deducted from results).
4.6.3.2 DC coil resistance (see 3.7.2). The dc coil resistance of choppers shall be measured in accordance with
method 303 of MIL-STD-202.
4.6.3.3 Coil impedance (see 3.7.3). The coil impedance of choppers shall be measured at +25°C with nominal
coil voltage and frequency using the voltmeter-ammeter method of equivalent.
4.6.3.4 Capacitance (see 3.7.4). The contact capacitance of the choppers shall be measured in accordance with
method 305 of MIL-STD-202. The following details and exception shall apply:
(a)
(b)
Points of measurement: Between switching contacts and coil, and between switching contacts and case.
4.6.3.5 Polarity (see 3.7.5). Apply dc voltage of predetermined polarity to specified drive coil terminals. Specified
contact closure (see 3.1 and 6.2.2) shall occur. DC voltage applied to the coil shall be 75 percent of rated coil root-
mean-square (rms) voltage.
4.6.3.6 Starting voltage (see 3.7.6). Each specimen shall be tested by the application of 120 percent of the rated
coil voltage at nominal frequency across the coil for a minimum of 20 minutes. This voltage shall then be removed
and within 1 minute, 80 percent of the rated coil voltage shall be applied. At the time the latter voltage is impressed
across the coil and for 5 minutes thereafter, the output-waveform of the specimen under test shall be observed on an
oscilloscope to determine immediate starting and continuous operation. The chopper shall not be jarred or vibrated
during the test.
4.6.3.7 Waveform characteristics (see 3.7.7). Waveform characteristics shall be tested as specified herein and
4.6.3.7.1 to 4.6.3.7.4 inclusive. The chopper waveform characteristics shall be measured by means of the circuit of
figure 2 or one with equivalent accuracy. The dwell time, dissymmetry, contact bounce, transfer time, and phase
angle shall be measured on an oscilloscope with a minimum diameter of 4 inches as shown on figure 3. Before
taking any measurements, and with the chopper armature shorted to the electrical contacts, the value of R1 will be
adjusted for a perfect circle on the oscilloscope. The value of R3 will be adjusted for the desired contact current level.
The coil voltage and frequency shall be varied in the ranges indicated in table III unless otherwise specified (see 3.1
and 6.2.2).
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