The role of the intermediate relay in the line

Update:24-08-2019
Summary:

In industrial control lines and current home appliance […]

In industrial control lines and current home appliance control lines, there are often intermediate relays. For different control lines, the role of three-phase relays is different. The functions of the intermediate relays are common in the following ways:
1. Replace the small contactor
The contacts of the intermediate relay have a certain load capacity. When the load capacity is small, it can be used to replace the use of small contactors, such as electric shutters and some small appliances. This has the advantage that it can not only serve the purpose of control, but also save space and make the control part of the appliance more delicate.
2. Increase the number of contacts
This is the most common use of intermediate relays. For example, in a circuit control system, the contacts of one contactor need to control multiple contactors or other components, but instead add an intermediate relay to the line.
3. Increase contact capacity
Although the contact capacity of the intermediate relay is not very large, it also has a certain load capacity, and the current required for its driving is small, so the intermediate relay can be used to expand the contact capacity. For example, it is generally not possible to directly use the output of the inductive switch or the triode to control the electrical components with relatively large loads. Instead, an intermediate relay is used in the control line, and other loads are controlled by the intermediate relay to achieve the purpose of expanding the control capacity.
4. Conversion contact type
In industrial control lines, such a situation often occurs. The control requires the use of a normally closed contact of the contactor to achieve the control purpose, but the normally closed contact of the contactor itself has been used up and the control task cannot be completed. At this time, an intermediate relay can be connected in parallel with the original contactor coil, and the normally closed contact of the intermediate relay can be used to control the corresponding components, and the type of the contact is switched to achieve the required control purpose.
5. Used as a switch
In some control circuits, the switching of some electrical components often uses an intermediate relay, which is controlled by the opening and closing of its contacts. For example, the automatic degaussing circuit commonly used in color TVs or displays, the triode controls the on and off of the intermediate relays, thereby achieving control degaussing. The role of the coil on and off.
6. Eliminate interference in the circuit
In industrial control or computer control lines, although there are various interference suppression measures, the interference phenomenon is more or less present.