PID is a closed-loop control system. This means that the controller continuously receives temperature feedback, compares it with the required setpoint and makes corrections in response.

The three elements of PID consider different aspects of the temperature response:

Proportional (P) responds to the current difference between the measured temperature and the setpoint. A larger difference generally requires a larger corrective response.

Integral (I) considers how long an error has been present and helps correct small, persistent differences between the actual temperature and the setpoint.

Derivative (D) considers how quickly the temperature is changing, helping the controller anticipate the direction of the process and reduce excessive overshoot.

These three elements work together to provide a controlled response rather than simply switching cooling fully on or off whenever the temperature moves away from the setpoint.

Process cooling applications often require more than simply making a fluid cold. The temperature may need to remain stable while the heat generated by the application changes.

PID control helps the chiller to respond to these changing conditions while keeping the process fluid as close as possible to the required setpoint.

For the user, this can provide:

• More precise temperature regulation
• Improved temperature stability
• Reduced temperature overshoot and fluctuation
• Controlled response to changes in process heat load
• More repeatable process conditions

This can be particularly important in laboratory, analytical, semiconductor, test and measurement, manufacturing, and other applications where changes in temperature can influence process performance or results.

The temperature stability that can be achieved depends on the specific chiller model, application, and operating conditions.

Applicable ATC recirculating chillers can provide temperature stability of ±0.1°C, making them suitable for applications where precise process temperature control is important.

Always check the technical specification for the particular chiller being considered, as temperature stability and operating range are product specific.

One of the purposes of PID control is to continually respond to what is happening within the system.

For example, if the process begins generating more heat and the fluid temperature starts moving away from its setpoint, the controller responds accordingly. As the temperature approaches the required setpoint, the response can be moderated to help minimise overshoot.

The precise way the chiller responds depends on its control system and refrigeration design, but the overall objective is the same: maintaining stable fluid temperature rather than simply providing maximum cooling continuously.

Stable temperature control can help to protect both the process and the equipment being cooled.

Depending on the application, temperature variation can affect measurement accuracy, repeatability, product quality, equipment performance, or process consistency.

A correctly specified recirculating chiller provides a controlled supply of process fluid at the required temperature, with PID control helping to maintain that temperature as operating conditions change.

For applications with particularly demanding temperature control requirements, discuss the required temperature range, stability, and process heat load with ATC when specifying your chiller.