Automatic and manual, no matter what the control is, a 1a500v bidirectional thyristor is connected in series to one connector of the coil of AC contactor, a 100k resistor is connected in series to the trigger pole of the thyristor, and then a reed is connected to the positive pole of the thyristor, and then one of the wires of the power supply is connected. The other end of the contactor coil is connected with the other end of the power line, which forms an automatic switch. If the controlled contactor is large, increase the thyristor and reduce the resistance of the control pole. When the magnet approaches the reed, the yellow tube closes, triggering the thyristor to turn on, the coil to turn on, the contactor to turn on, and the controlled electrical appliance to supply power. On the contrary, when the magnet is removed, the contactor will cut off power and stop power supply. If manual control is used simultaneously, a manual switch will be connected in series between the dry yellow pipe and the power supply. This switch is used to switch between automatic and manual operation. Then a manual switch will be connected between the power line and the contactor coil to realize manual operation.

In order to control AC contactor automatically and manually, it is necessary to use time relay, pressure relay, temperature sensor, flow sensor, travel switch, intermediate relay, etc. which can be connected into normally closed or normally open state in other forms to provide closed circuit for the circuit. Here I take the simplest water supply pump, using the electrode installed in the pool as an example, to talk about its automatic and manual control principle. Familiar with it, you can draw inferences from one instance for other circuits, a good understanding of its working principle.

When starting manually, first put the manual / automatic selection switch SA in the "manual" position to prepare for manual work. Press the start button SB2, the normally open contact is closed, the power supply of the KM coil circuit of the AC contactor is connected, the KM coil is powered on, the KM auxiliary normally open contact is closed and self-locking, the KM three-phase main contact is closed, and the water supply pump motor is powered on to start operation. When the water level is controlled automatically, the manual / automatic selection switch SA is set at the "automatic" position to prepare for the automatic work. Turn on the control switch s to control the power supply of the transformer (for safety, the isolation transformer is used here to reduce the voltage to 24 V).

When the water level in the water tank is lower than the medium water level M, because there is no water between the medium water level M electrode and the low water level electrode L, the Ka coil of the intermediate relay will be cut off and released, the normally closed contact of Ka will return to the normally closed state, the power supply of the KM coil circuit of the AC contactor will be connected, the KM coil will be powered on, the three-phase main contact of KM will be closed, the water supply pump motor will be powered on, and the water pump will inject water into the water tank. At the same time, the KM auxiliary normally closed contact is disconnected, which cuts off the channel between the middle water level M and the high water level h. When the water level in the water tank rises to the middle water level, the control circuit will continue to work. As the water level continues to rise, when the water level in the water tank rises to the high level electrode h position, the water in the water tank will connect the high level electrode and the low level electrode L, and connect the intermediate relay Ka coil circuit power supply, Ka coil is powered on and closed, Ka normally closed contact is disconnected, AC contactor km coil circuit power supply is cut off, KM coil is powered off and released, KM phase main contact is disconnected, water supply pump motor is powered off and stops running, water pump stops filling water into water tank.

At the same time, KM auxiliary normally closed contact is restored to normally closed state, which not only ensures that the water supply pump motor can not start to work from high water level to medium water level, but also ensures that the pump can be started again to inject water into the water tank from below medium water level. When the water level in the water tank is lower than the middle water level, there is no water between the middle water level electrode m and the low water level electrode L. in this way, the Ka coil of the intermediate relay is de energized and released, and the normally closed contact of Ka is restored to normally closed, so that the KM coil of the AC contactor is powered on, the three-phase main contact of KM is closed, the electric motor of the water pump is powered on, and the water pump injects water into the water tank, so that the water level is controlled automatically. The selection of manual and automatic operation modes is realized by the transfer switch SA1.

The no-load process is as follows

When SA1 is turned to manual, → contact (1, 3) is closed, → relay KA is pulled in → Ka contact (3, 1-51) is closed, manual preparation is completed, press button SB2, 1km to pull in and self lock, press button Sb4, 2km to pull in and self lock, press button SB1, 1km to open, press button SB1, 2km to open.

When SA1 is turned to manual mode, → contact (1, 5) is closed. At this time, contactor 1km and 2km are directly controlled by the contacts of relay fj1 and fj2, and the control signals of relay fj1 and fj2 are provided by the outside to realize automatic control.