Question

What is the forward control circuit of relay control? Analysis of the working principle diagram of the forward rotation control circuit of relay control

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Relay principle and implementation method

First: ordinary relay

Relay is an automatic switch that controls high voltage and large current through low voltage and small current.

The structure of the relay includes: A is the electromagnet, B is the armature, C is the spring, D is the moving contact, and E is the static contact.

Answer 1

Relay control forward control circuit working principle diagram analysis:

1. Start preparation: press the button SB2, the contactor KM coil is energized, the KM main contact and two normally open auxiliary contacts are closed, the KM main contact is closed for the inverter to turn on the main power supply, one KM normally open normally open auxiliary contact is closed, the locked KM coil is energized, and the other KM normally open auxiliary contact is closed, which prepares for the relay K intermediate A coil to be energized.

2. Forward control: press the button SB4, the relay KA coil is energized, 3 KA normally open contacts are closed, 1 normally open contact is closed to lock the KA coil to get electricity, 1 normally open contact is closed short button SB1, there is a normally open contact closed connection STF, SD terminal, equivalent to STF terminal input forward control signal, inverter U, V, W terminal output forward power supply voltage, drive motor running in the forward direction. By adjusting the potentiometer R connected to this terminal, the output power frequency of the frequency converter changes, and the speed of the servo motor also changes.

3. Inverter abnormal protection: If the inverter fails during the abnormal period, the internal equivalent normally closed switch between the B and C ends of the inverter is disconnected, the contactor KM coil is de-energized, the KM main contact is disconnected, the inverter input power is cut off, the inverter is protected, and the relay KA coil is also powered off, and the 3 KA normally open contacts are disconnected.

4. Shutdown control: when the inverter is working normally, press the button SB3, the KA coil loses power, the KA 3 normally open contacts are disconnected, one of the KA normally open contacts is disconnected and cut off STF, SI) terminals are turned on, the inverter stops the output power supply, and the servo motor stops.

Answer 2

How the relay works:

When the relay is working, the electromagnet is energized, and the armature is sucked down to make D and E contact, and the working circuit is closed. When the electromagnet is powered off, it loses its magnetism, and the spring pulls the armature up to cut off the working circuit. A common relay is a switch that uses electromagnets to control the on/off of the working circuit.

Advantages of the control circuit implemented by the relay: control the high voltage with low voltage; remote control; Automatic control.

1. Main technical parameters of relay:

(1) Rated working voltage: the voltage required by the coil during normal operation. Depending on the model, DC voltage is generally used, but AC relays can use AC voltage.

(2) DC resistance of relay: refers to the DC resistance of the coil in the relay.

(3) Contact resistance of relay: refers to the resistance value after contact of the contact in the relay. The resistance value is generally small and can be measured with a low-resistance meter and a four-wire measurement method.

(4) The absorption (action) current or voltage of the relay: refers to the minimum current or minimum voltage that the relay can produce the absorption action. Under normal circumstances, the input current must be greater than the pull-in current to allow the relay to work stably. Note: The working voltage cannot exceed 1.5 times the rated working voltage.

(5) The release current or voltage of the relay: refers to the maximum current or maximum voltage of the relay to produce the release action.