Downloaded from https://www.everyspec.com MIL-STD-1311D FIGURE 6. DC charging circuit without charging diode. b. Without charging diode (see figure 6 ). The charging current waveform shall be examined on a suitable oscilloscope, as the voltage developed across a noninductive resistor inserted in series between the normally connected power supply return and ground. The charging waveform for frequencies above half the resonant frequency appears as a series of lobes jointed at cusps and the instantaneous value of the current at the tip of each cusp is zero when the frequency is at the resonant value (see figure 7 ).
The approximate value of the resonant frequency for this purpose may be obtained either by calculation or by a preliminary run with low voltages. FIGURE 7. Charging current waveform without charging diode. 4.12.2.3 Trigger source impedance. The impedance of trigger sources employing a line-type modulator (gas tube circuit) shall be measured by the short-circuit current method or the matching resistor method, indicated below. The impedance of trigger sources employing a high-vacuum tube, cathode follower (or similar circuit) shall be measured by the short-circuit method only. a. Short-circuit current method. The equivalent trigger circuit shown on figure 8 shall be used.
The voltage from B to C (eBC) shall be measured with the switches SW1 and SW2 open. Switch SW1 shall then be closed and the voltage from A to C (eAC) shall be measured. The short-circuit current shall then be determined from: Zext eAC is = The trigger-source impedance (Zs) is then: Zext eAC eBC is eBC Zs = = b. Matching resistor method. The equivalent trigger circuit shown on figure 9 shall be used. With SW1 and SW2 open, measure the open-circuit voltage from B to C (eBC). A noninductive resistor shall then be inserted in series with SW1 between B and C. Close SW1. Adjust R until the measured voltage across BC equals one-half the open circuit voltage.
The trigger source impedance, Zs, is then equal to the value of the resistance inserted. 11