Abstract: This paper introduces the isolation function of intermediate relays, which are most widely used in engineering practice. Common problems encountered in the use of intermediate relays in equipment are analyzed through engineering examples, and solutions are proposed. Keywords: Relay; Isolation function; Problems; Solutions With the continuous improvement of industrial automation, production processes place higher demands on the reliability of automatic control systems. A large number of intermediate relays are used in automated control systems, and their reliability is crucial to the overall reliability of the control system. How to use intermediate relays appropriately and reasonably is the foundation for the reliable operation of the control system and a major prerequisite for achieving intelligent operation. 1 Control Function Intermediate relays are actuators that play a control and isolation role in automatic control circuits. They are widely used in remote control, telemetry, communication, automatic control, mechatronics, and power electronic equipment, and are one of the most important control components. Relays generally have a sensing mechanism (input section) that reflects certain input variables (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc.); an actuator (output section) that controls the "on" and "off" states of the controlled circuit; and an intermediate mechanism (drive section) between the input and output sections that couples and isolates the input, processes the data, and drives the output. In engineering practice, intermediate relays mainly serve two purposes: isolation and adding auxiliary contacts. Adding additional contacts is relatively rare in practical applications because modern contactors can have many additional pairs of auxiliary contacts with reliable operation, making it unnecessary to add auxiliary relays to general control circuits. Isolation is more commonly used in current control systems. The author believes that isolation mainly involves two aspects: first, dividing a control loop into two or more relatively independent loops; and second, converting high-voltage analog signals into switching quantities (active or passive) through intermediate relays. This article does not emphasize the functions of these relays, but rather analyzes the technical problems in the application of intermediate relays through engineering examples and proposes solutions. [b]2 Working Principle[/b] The working principle of an intermediate relay is to transform an input signal into one or more output signals. Its input signal is the energization or de-energization of the coil. Its output is the action of the contacts (the normally open contacts close, and the normally closed contacts open). Its contacts are connected in other control circuits, and the change of the contacts causes the control circuit to change (e.g., conduction or cut-off), thereby achieving the predetermined control or protection purpose. In this process, the relay mainly plays the role of transmitting signals. 3 Working Characteristics As a control element, the relay has the following four characteristics: (1) Expanding the control range. For example, when the control signal of a multi-contact relay reaches a certain value, it can simultaneously switch, open, and close multiple circuits according to different forms of contact groups. (2) Amplification. For example, intermediate relays can control a high-power circuit with only a very small control quantity. (3) Synthesizing signals. For example, when multiple control signals are input into a multi-winding relay in a specified form, they are compared and synthesized to achieve the predetermined control effect. (4) Automatic, remote control, and monitoring. For example, relays on automatic devices, together with other electrical components, can form a program control circuit to achieve automated operation. 4. Application Examples Taking the automatic control of a conveyor belt machine as an example, we introduce the isolation function of intermediate relays. The schematic diagram is shown in Figure 1. The conveyor belt machine adopts two control modes: automatic (interlocked) and manual (single machine). The automatic and manual modes are switched by an automatic selector switch. The conveyor belt machine is equipped with pull-cord switches, slippage protection, etc., and these signals are all connected to the PLC control system. We notice that the normally open signal of the 1-SK emergency pull-cord switch is directly sent to the PLC input module. Since the 1-SK emergency pull-cord switch is a 220V signal, the PLC input module must be selected with a rated voltage of 220V. In practical applications, the inrush current generated by the emergency pull-cord switch is relatively large, which can easily burn out the input module. When we cleverly utilize the isolation function of the intermediate relay to convert the high-voltage analog signal into a switching signal through the intermediate relay, we can easily solve this problem (control principle is shown in Figure 2). In Figure 2, the 1-SK emergency pull rope switch signal is not directly sent to the PLC input module. Instead, it is switched via intermediate relay 1-L1, and a 24V signal is sent to the PLC input module through the auxiliary contact of intermediate relay 1-L1. This cleverly utilizes the isolation function of the intermediate relay, ensuring the reliability of the PLC input module and extending its service life. However, Figure 2 has a drawback: when the system is in manual control mode, if the operator does not follow the operating procedures and does not activate the electric bell alarm before starting the conveyor belt, the conveyor belt can still start normally. Since workers are easily caught in the conveyor belt while it is operating, causing personal injury accidents, an alarm is needed before starting the conveyor belt to allow workers to evacuate quickly and avoid accidents. As engineering designers, we must prevent such accidents in the design of the automatic control of the conveyor belt. The control process must ensure that the operator activates the electric bell alarm before starting the conveyor belt; if the electric bell alarm is not activated, the conveyor belt cannot start. This avoids accidents caused by operator error. Based on this idea, we add an intermediate relay to solve this problem (see Figure 3). The control flow is as follows: Set the selector switch to manual control, press the start alarm bell button, energize coils 1-SB3 and 1-L2, close 1-L2, and the bell will sound an alarm; then press the start button 1-SB1 to start the conveyor belt. If the start alarm bell button 1-SB3 is not pressed, 1-L2 will always be in the open state. Even if the start button 1-SB1 is pressed, the AC contactor 1-KM coil will not be energized, and the conveyor belt will not start. In this way, even if the operator misoperates, it will not cause an accident, eliminating hidden dangers and ensuring safe production. 5 Conclusion In summary, through in-depth research and analysis of the problems encountered in the use of intermediate relays, and by skillfully utilizing the signal transmission and isolation amplification functions of intermediate relays, the reliability and performance of the system can be improved. Relays are widely used in industrial production, and their close integration with computers adds even more vitality, enabling relays to better serve industrial production. Click to download: A Brief Discussion on the Isolation Function of Intermediate Relays Editor: Chen Dong