Inductor coil short circuit test circuit

This instrument is used to test internal short circuits of transformers below several hundred volt-amperes. The circuit is simple and easy to make and debug.
    The electrical schematic diagram of the instrument is shown in Figure 6-15. In the figure, the transistor VT, the inductor L, the capacitors C4, c5, etc. form a capacitor three-point oscillation
circuit. When the inductor coil under test is connected across the oscillation circuit end, if there is no internal short circuit, it will show high impedance and will not affect the operation of the oscillator. At this
time, the milliamp meter reading will change little. If there is a short circuit inside the coil under test, the impedance will be low, which will reduce the Q value of the oscillation circuit, causing the oscillation
to weaken or stop. At this time, the reading of the milliamp meter will drop rapidly. In the figure, R; (current limiting), vs (voltage stabilization) and Ci (filtering) constitute a simple regulated
power supply.
    The current amplification factor of VT should not be less than 100. L can use MX0-2000-GU36×22 pot-shaped core, with Wah Ding. 35mm
enameled wire wound with 120 turns. In order to reduce the size, a 9V laminated battery can be used as the power supply.
The milliammeter can be replaced by the corresponding current range of the multimeter. The remaining components
are selected according to the models or parameters shown in the figure.
  All components are designed and installed on a small printed circuit board, and the whole machine
can be installed in a delicate soap box or a small case designed and made by yourself
. The switch S and the test rod socket of the milliammeter should be installed on the casing for easy
access.
  The debugging steps are as follows.
  First adjust the resistance of RP1 and RP2 to the maximum, then slowly reduce
the resistance of RP1. At this time, the reading of the milliamp meter should rise; when the current of the milliamp meter rises to
0. 4mA, and then continues to reduce the resistance of RP1, the reading of the milliamp meter will
suddenly jump to 1_ 2 ~ 1. 4mA. This It means that the oscillator has started to vibrate. Then adjust RP2 so that the milliammeter reading is 1.4-1. 6mA. Finally
, a transformer is artificially short-circuited (that is, a wire is passed through the gap between the wire package and the core for 1 to 2 turns, and connected end to end to form a
short-circuit ring), and the test is carried out. The reading of the milliammeter should be from 1. 4mA suddenly drops to o. 4mA; if it only drops to 1.2mA, it means that the oscillation amplitude of VT
is too large . At this time, the resistance of RP1 should be increased until the mA meter drops to about 0.4mA. At this time, the adjustable resistor RP1 can be blocked. Debugging is over.