Implementing Analog PID Closed-Loop Temperature Control with Coolmay EX3S

An industrial oven that needs to hold 185 °C ± 2 °C for a curing process won't get there with a simple ON/OFF thermostat. The temperature swings of ±15 °C produce inconsistent product and waste energy. A PID closed-loop using the Coolmay EX3S built-in analog I/O eliminates the oscillation and typically cuts energy consumption by 10 to 15 percent while holding the setpoint within specifications.

The system needs three components: a temperature sensor with a 4–20 mA transmitter connected to analog input AI1, the EX3S itself running the PID algorithm, and an actuator—either a VFD controlling a fan motor through analog output AO1 (0–10 V) or a modulating valve through AO2.

Tuning the PID loop follows the Ziegler-Nichols method, which works well for most thermal processes. Set the proportional gain to 1, integral time to 0, and derivative to 0. Apply a 20 °C step change to the setpoint and observe the response. Increase the proportional gain until the temperature oscillates at a steady amplitude. Record that critical gain (Ku) and the oscillation period (Tu). Then calculate the PID parameters as follows:

• Proportional band: 0.6 × Ku
• Integral reset time: 2.0 × Tu (in milliseconds)
• Derivative time: 0.125 × Tu (start with PI only and add derivative if needed)

The EX3S implements PID through function code 88 (the PID instruction). The setpoint goes into D100 (scaled to 0.1 °C resolution), the process variable comes from the analog input via a FROM instruction into D200, and the PID parameter table starts at D300. The output value in D400 writes to the analog output through a TO instruction. For temperature loops, a sample time of 200 to 500 ms works well, and limiting the output to 5–95 percent range prevents integral windup.

With the Coolmay EX3S-24MT-4AI2AO, you get two analog inputs and two analog outputs built into a single device that also runs the HMI and the logic. No dedicated temperature controller is needed, which simplifies the panel and reduces total system cost.

Request a quote for the complete temperature control kit including the EX3S, K-type transmitter, and wiring harness. Download the PID sample code with ladder logic and HMI faceplate ready to deploy.