Acoustic power failure indicator
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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Recently, due to the frequent cases of the so-called "fan" power outages, the problem of operational control of the presence of voltage in the lighting network has become relevant. Descriptions of devices of similar purpose on microchips have already been published in Radio.
I propose a variant of the simplest signaling device on a thyratron with a cold cathode MTX90. The device (see figure) is a relaxation oscillator based on the VL1 thyratron, powered from the mains through a VD2 diode rectifier. Oxide capacitor C2 smoothes the ripple of the supply voltage. It also serves as a power source for the generator in the event of a power failure in the network.
When the mains voltage is present, then a negative voltage rectified by the VD6 diode is applied to the thyratron grid through the resistor R1, which disrupts the oscillations of the relaxation oscillator. When the mains voltage fails, the capacitor C1 discharges much faster than the capacitor C2. The voltage on the grid that disrupts the generation disappears, and a sound of a gradually decreasing tone is heard in the dynamic head HA1 for 15 ... 20 s.
The whole device can be assembled in the case of a small-sized subscriber loudspeaker using the dynamic head available there, a matching transformer and a variable resistor.
Before being installed in the device, the thyratron is subjected to "training" for at least 24 hours. To do this, it is supplied with a constant voltage of 200 ... 300 V through a resistor with a resistance of about 100 kOhm, having previously closed the cathode and the grid. This procedure can be done directly in the device by connecting the anode of the thyratron to the right (according to the diagram) terminal of the resistor R3.
Setting up the device comes down to adjusting the tuning resistor R4 - when an alternating voltage is applied to the input in the range of 200 ... 240 V, the signaling device should be "silent", and when the power goes out, a sound will appear. Variable resistor R7 set the required volume.
If the turn-on delay is too long, the capacitance of the capacitor C1 can be reduced to 0,33-0,47 uF. If the device is unstable, select the resistance of the resistor R5.
In the case, you can cut a hole for the cap of the thyratron, then its glow will additionally signal the presence of mains voltage.
When setting up the device, care should be taken, since its circuits have a galvanic connection with the mains.
Author: A.Sharonov, Chita
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