Purpose and classification of control relays

   The purpose and classification of the control relay The control relay is an automatic electrical appliance which is suitable for remote switching and disconnecting ac and DC small capacity control circuits and is used for control, protection and signal conversion in the power drive system.The input of the relay is usually electric quantity such as current, voltage, etc., but it can also be non-electric quantity such as temperature, pressure, velocity, etc. The output quantity is the electrical signal or parameter change of the output circuit when the contact ACTS.
　　The characteristic of relay is that when the change of its input reaches a certain program, the output will have a step change.Control relays are used for a wide variety of purposes and are conventionally divided into the following categories according to their inputs:

　　(1) Voltage relay it is based on the circuit voltage changes and action of the relay such as for motor loss, undervoltage protection of AC/DC voltage relay for winding motor braking and reversal control of AC voltage relay for DC motor reversal and reverse braking DC voltage relay.The intermediate relay used to increase the number or capacity of contacts in the control circuit is essentially a voltage relay except that its operating value does not need to be adjusted.

　　(2) current relay it is based on the circuit current changes and action of the relay is used for motor and other load overload and short circuit protection, as well as dc motor magnetic field control or loss of magnetic protection.

　　(3)Time relay this is a relay that has a certain time interval from the reception of signals to the action of the executive elements, such as the motor used to delay switching starting resistance, motor energy brake and production process of the program control used by the relay

　　(4)Thermal relay a relay for ac motor overload and broken phase protection.

　　(5)Temperature relay A relay used by various equipment for overheat protection or temperature control.

　　(6)Speed relay Power supply motor speed and steering change monitoring relay.

　　Edit the main technical parameters of this section

　　1 rated parameters it refers to the input of the rated value and the rated voltage and rated current of the contact rated work, contact on and off capacity, mechanical and electrical life of the relay.

　　⑵The two action parameters and setting parameters input value of action and return value collectively action parameters such as suction voltage current and release voltage current, action temperature and return temperature, etc.The action parameters that can be adjusted are called setting parameters.

　　The return coefficient (3) is the ratio of the return value of the relay to the action value.The return coefficient calculated by current is the ratio of the return current to the action current. The return coefficient calculated by voltage is the ratio of the return voltage to the action voltage.

　　(4) Reserve coefficient the rating of relay input or the ratio of normal working value and action value is called reserve coefficient also called safety coefficient.In order to ensure the reliable operation of the relay without misoperation, the reserve coefficient must be greater than 1, generally 1.54.

　　5 (5) sensitivity it refers to the power or coil magnetomotive force required for relay operation.For the convenience of comparison, the required operating power or operating ampere-turns of each pair of normally open contacts are sometimes used as the sensitivity index.Electromagnetic relay with low sensitivity and higher operating power of semiconductor relay with higher sensitivity requires only 0.000001w.

　　6 action time relay action time refers to the absorption time and release time.The time interval from the time when the relay receives the control signal to the time when all the contacts reach the working state is called the closing time and the time interval from the time when the relay receives the control signal to the time when all the contacts return to the release state is called the release time.According to the length of action time relay can be divided into two types: instantaneous action type and delay action type.