How to Control a 3-Phase Heater by SCR Temperature Controller with 4-20ma Signal?

In industrial heating systems, precise control of power delivery to heating elements is essential for maintaining optimal performance. One of the most common ways to regulate heating power is by using an SCR (Silicon Controlled Rectifier) power controller in combination with a temperature controller that has a 4-20mA output signal. This setup provides efficient, continuous power regulation, enabling precise temperature control and extending the lifespan of the equipment.

In this article, we’ll guide you through the typical wiring configuration for an SCR power controller when paired with a 4-20mA temperature controller. (Click to view another common wiring with DC input signal.)

1. Main Circuit - Connecting the Heater to the SCR Controller

The main power supply for the heater is connected to the SCR power controller’s input terminals. Here’s how to wire the main circuit:

• Three-Phase Power Supply: The three-phase AC power is connected to the SCR controller through the large terminal screws located at the top of the controller. This terminal is typically marked as "L1, L2, L3" or similar, depending on the model.
• Output to Heater: From the SCR controller, the power is passed to the heating elements through the larger output terminal screws at the bottom of the SCR controller. These are marked as "U, V, W" (or similar), which correspond to the three-phase input.

This configuration allows the SCR controller to modulate the power delivered to the heater based on the signal received from the temperature controller, enabling accurate and efficient heating control.

2. Temperature Controller – Using a 4-20mA Output Temperature Controller

The temperature controller plays a critical role in the regulation of the heating system. For this setup, we’ll use a standard temperature controller with a 4-20mA output signal. Here’s how to wire it to the SCR power controller:

• Connect the Signal to the SCR Controller: Connect the positive terminal of the temperature controller's 4-20mA signal to Terminal 2 on the SCR power controller, and the negative terminal to Terminal 4.

By using a 4-20mA signal, the SCR controller can receive temperature feedback from the controller and adjust the output power to the heater accordingly, providing continuous regulation based on real-time temperature changes.

3. Power Supply – Connecting the SCR Power Controller

The SCR power controller requires a separate 220V AC power supply for operation. Here’s how to wire the power supply:

• Connect the Live (Phase) Wire: Terminal 20 is where you connect the live (phase) wire from the 220V AC power supply.
• Connect the Neutral Wire: Terminal 21 is where you connect the neutral wire from the power supply. This ensures proper operation of the SCR controller and the correct flow of electricity.

The SCR controller requires a stable power supply to manage the switching and modulation of the heating elements effectively. Proper power connection ensures smooth operation and prevents disruptions in the heating process.

4. Program Settings – Configuring the SCR Power Controller

To configure the SCR controller to work with the 4-20mA signal from the temperature controller, you’ll need to adjust the settings through the SCR controller’s operation interface. Follow these steps:

• Input Signal Selection: Access the controller’s settings menu and locate the parameter for input signal selection, typically labeled as A02 (Input signal selection). This controls which type of signal the SCR controller will use to regulate heating power.
• Set to Analog Input 1 (AI1): Change the setting to AI1 (Analog input 1). This allows the controller to receive the 4-20mA signal from the temperature controller and use it for power modulation. By adjusting this setting, the controller will now respond to temperature changes and modulate the power to the heater accordingly.

Conclusion

Connecting an SCR power controller with a 4-20mA temperature controller is one of the most efficient ways to regulate heating power in industrial applications. By wiring the components correctly and configuring the SCR controller to respond to the temperature controller's signal, you can achieve precise, reliable, and consistent temperature control. This setup reduces energy waste, improves heating efficiency, and helps extend the life of the heating elements.

With proper installation and configuration, this system provides a seamless solution for controlling heating processes in industries ranging from manufacturing to food processing, offering both operational flexibility and energy savings.

This guide should provide a solid understanding of how to wire and configure an SCR power controller with a 4-20mA output temperature controller for heating applications. If you have any further questions or need assistance with your system setup, feel free to reach out to us!