Talking about collocation by hand control

There is no doubt that any energy can be said to be a signal source, but there is a special field of use that artificially "thinks" many vulgar city concepts. Take an audio power amplifier as an example. The first stage is the signal of the second stage, the second stage is the signal of the roof of the world, and the last stage is the signal of the horn. There is no essential difference between "signal relay" and "power relay". For motors below1000W, relays with low current can be used for control, but relays with current above 10A are sometimes called AC contactors and can be called power relays. But for the contactor of 1000A, the relay of 10A becomes a signal relay. Then, no matter how big the magnetic relay is, it is a signal that provides current to the coil. The battery can naturally excite the DC relay coil, which is naturally a signal source. In addition, if the voltage is high, but its internal resistance is also surprisingly high, this time is usually called "voltage signal", so some people think that tiny power is called signal source, which is also relative. Compared with crystal receiver, transistor radio is a high-power equipment, but compared with stage sound, it has become a signal.