The strong and weak current can be used as the basis for the protection action of circuit or electrical components, and also can reflect the control signals of other physical quantities such as clamping force or torque. Usually, the current control is realized by means of current relay. When the current in the circuit reaches a predetermined value of the dish, the contact action of the current relay and the switching circuit can achieve the purpose of current control. Figure 1 is a Longmen planer using current control to achieve automatic clamping of the beam line. Pull the clamping handle, S Ti is pressed, clamping motor is rotating, clamping; when the clamping force reaches a predetermined value, KA action, automatically cut off the KMl coil loop, stop clamping.
Several basic electrical control circuit of the above we introduce in fact corresponds to the four general principles of control, namely the travel time control principle, control principle, current control principle and speed control, simply summarized as follows:
1) the stroke control principle is that the working state of the circuit is controlled by the stroke switch according to the stroke or position of the moving parts of the production machinery.
2) time control principle is based on the production process requirements, the use of time relay, cable connector at a certain time interval to send a switching signal, control the working state of the circuit.
3) the current control principle is based on the main loop current changes, the use of current relay control circuit operation.
4) speed control principle is based on the motor speed changes, the use of speed relays and other appliances to control the operation of the motor.
It should be noted that the above general control principles do not contradict each other and are independent of each other in practical application, but are often combined to form a composite electrical control circuit.