Sub-ultrasonic remote control switch circuit

There are many brands and circuit forms of sub- ultrasonic remote control switches . Some control actuators use relays ; others use thyristors. Most remote control transmitters use compressed air subsonic flutes (which have olive-shaped and oblate shapes). This article takes the typical circuit shown in the attached figure as an example to introduce its working principle and two examples of troubleshooting.

1. Circuit

AC220V is stepped down by C1, rectified by VD1 and VD2; filtered and stabilized by C2 and VD3, it provides working power for the receiving control circuit. BM is a piezoelectric sub-ultrasonic receiving sensor; R2 and L form a sub-ultrasonic resonant circuit; VT3 and VT4 form a bistable trigger; VT5 and relay K form a control execution circuit; CZ is the controlled load socket.

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2. Maintenance examples

[Example 1] After receiving the remote control command from the transmitter, the indicator light VD7 and the controlled bulb flash rapidly and continuously at the same time, and the mechanical noise generated when the relay armature trembles can be heard. After 1 second, the trembling stops and the controlled The light bulb and VD7 go out at the same time.

This kind of fault often occurs in the power circuit of the remote control switch. When the mains voltage is lower than 180V or the capacity of the step-down capacitor C1 is insufficient, the DC power supply is insufficient to provide the required operating current to the whole machine, causing the drive to malfunction. It is difficult for the circuit and relay to enter the normal suction state smoothly, which is manifested as weak suction, seeming to be sucked but not sucking, etc.

It was tested that the mains power was normal, so C1 was removed and its capacity was measured to be 0.32μF. The capacitance has been significantly reduced. Replace it with a 0.47μF/400V polyester capacitor and troubleshoot.

In addition, if C2 fails (no capacity), it will also cause the same fault phenomenon as in this example.
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[Example 2] Each time the light is turned on remotely, the indicator light VD7 and the controlled bulb must flash several times before entering a stable lighting state.

In the trigger pulse generation circuit, R3 is the collector load resistance of VT2, and the trigger signal is output from R3; C5 is to prevent mis-transmission.

In this example, C5 failed. After replacing it with a 2.2μF/16V electrolytic capacitor, the fault was eliminated. Practice has proved that the value range of C5 is generally between 0.47~3.3μF. Generally speaking, when the capacity is selected larger, the response time of the remote control switch is longer, and vice versa.