How to Set PT100 Decimal Display and Hysteresis in TCN4 Temperature Controllers

In industrial applications, temperature precision is critical—especially when using PT100 sensors. In this guide, we'll walk through how to configure your TCN4 series temperature controller to display decimal points for PT100 input and how to fine-tune the hysteresis (HYS) value in ON/OFF control mode.

✅ Step 1: Enable Decimal Display for PT100

When using a PT100 sensor, the TCN4 allows switching between integer display and 1-digit decimal display. To enable decimals:

1. Power on the controller and press and hold the SET key for 3–5 seconds.
   
2. When Par2 appears, release the button.
   
3. Use the ▲ key to scroll and find dPt.L.
   
4. Press SET again, hold for 3–5 seconds.
   
5. The screen will now switch to PT100 input with 1-digit decimal resolution.
   

This allows more precise control and visual accuracy in sensitive applications like HVAC, food processing, or lab environments.

✅ Step 2: Set Hysteresis in ON/OFF Control Mode

Hysteresis (HYS) defines how far below the target temperature the system must drop before turning back ON after reaching the upper limit. This prevents frequent switching, which can damage relays or cause instability.

1. Enter the basic setting mode (SET key → hold 3–5 seconds).
   
2. Locate the HYS parameter.
   
3. Adjust it based on your tolerance, e.g., HYS = 1.0°C means the output will re-engage when temperature drops 1.0°C below the setpoint.
   

This function is particularly useful for ON/OFF control, ensuring system stability and longer component life.

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