Electric spark timer

The spark timer described in this example can be used to measure gravitational acceleration as well as to demonstrate experiments in which air is punctured by high voltage or flammable gas.
Circuit Operation Principle The spark timer circuit consists of a power switch S, a diode VDl-VD6, a Zener diode VS, a thyristor VT, a resistor Rl-R3, a capacitor C, a step-up transformer T and a discharge electrode, as shown in Figure 8-155. Shown.

Turn on the power switch S. When the AC power is halfway positive, the current forms a loop through VDI, Rl, C, and VD3, and C starts charging. During the negative half cycle of the AC current, the current loops through VD4, R2, R3, VT, and VD2, causing the VT to be triggered to conduct. After VT is turned on, C discharges through the secondary winding of T, VD6, and VT, generating a high voltage of about 3OkV across the secondary winding of T, and generating an electric spark between the two discharge electrodes. Since the AC cycle is 0.02 s, it is fired once every 0.02 s.
During the experiment, if a conductive annular paper disk and paper tape soaked with black graphite powder solution are placed between the two discharge electrodes, each time the electrode is fired, a black spot of graphite powder is left on the paper tape as Experimental record.
Component selection
Rl selects lW metal film resistor, R2 and R3 select 1/4W metal film resistor for use.
C selects a polyester capacitor with a withstand voltage of 400V.
VDl-VD6 selects lN4007 silicon rectifier diode for use.
VS selects ZW58 type silicon steady voltage diode.
VT selects BTl69 type thyristor.
T uses a step-up transformer for electric batons.
S selects 5A, 220V power switch.