SU152137A1 - Probe Pulse Generator for Flaw Detector - Google Patents

Description

In modern ultrasonic pulse flaw detectors, shock excitation generators are used to form probing pulses, with tiratrons or electron tubes being used as key elements in the circuits of such generators. The use of electron tubes and thyratrons requires high-voltage power supplies; a significant consumption of lamp circuits reduces the efficiency and impairs the efficiency of the circuit. In addition, the amplitude of the pulse arriving at the piezoelectric element in existing schemes does not exceed the voltage of the generator power source.

The proposed probe pulse generator for a flaw detector provides an increase in the amplitude of the generated voltage due to the fact that part of the turns of the loop coil to which the capacitance is connected by an autotransformer circuit is tuned to the resonant frequency of the loop.

FIG. 1 is a schematic diagram of a pulse generator; in fig. 2 is a diagram of a pulse generator operating in a standby mode with synchronization from a source of trigger pulses.

The parallel circuit of the generator is formed by the inductance L and the capacitance of the piezo emitter PI. Diverting from a part of the coils LI through the switching diode of the D ppn structure is connected to the storage capacitor C. Capacity charge occurs through the resistance R connected through a switch to the power supply battery B.

The generator operates in self-oscillating mode. When the battery voltage is 10-20% of the threshold turn-on voltage

No. 152137

diode D, after switching on the diode, the capacitance C is discharged onto a part of the VITKOV / - generator circuit. The preliminary parallel circuit formed by the storage capacitor C and the generator part LI is tuned to the same frequency as the circuit formed by the inductance L and the piezo detector capacity PI. Since capacitance C is connected to inductance L by an autotransformer circuit, the voltage on the inductance leads and on the plates of the piezoelectric element PI will be greater than the voltage on capacitance C. At the same time, in the circuit LjC and, accordingly, in the circuit L oscillations occur at the ultrasonic frequency.

After the discharge of capacitance C, the diode D is restored, and the circuit returns to its original state. The duration of the pulse repetition period is determined by the constant time of the charging circuit, the voltage of battery B and the threshold voltage of diode D. The voltage of the storage capacitor C can be increased by sequentially turning on several diodes with a corresponding increase in battery voltage.

In the circuit depicted in FIG. 2, applied three series-connected diode type DP2-60; A positive trigger pulse with an amplitude of the order of 5V is applied to diode D1, which opens and thereby increases the potential difference across the diodes. Yes, the DZE diodes in turn open and a discharge of capacitance C per circuit occurs. The battery voltage to ensure the standby mode of the circuit is chosen less than the total potential of opening the diodes

D1-Dz.

In the assembled circuit, when the battery voltage is 6,120, the pulse amplitude is 270 volts.

The described generator circuit for an ultrasonic flaw detector made on semiconductor devices is economical and allows the use of low-voltage power sources. The principle of the circuit is based on the ability of pnp structure diodes to reduce their internal resistance to ten ohms when a certain potential difference is applied to the diode in the range of 10-100 V, depending on the type of diodes.

Subject invention

A probe pulse generator for a flaw detector made according to a circuit with shock excitation on semiconductor diodes of a pnp structure, characterized in that, in order to increase the amplitude of the generated voltage, a part of the turns of the loop coil to which the capacitance is connected by an autotransformer circuit, tuned to the resonant frequency of the entire circuit.

L

s

1

.and,

te

:

Oi

Fig 2