Controlling process temperature with accuracy and without extensive operator involvement is a crucial task in the heat treat shop and calls for the use of a temperature controller, which compares the actual temperature to the desired control temperature, also known as the setpoint, and provides an output to a control element. This comparative process relies upon an algorithm, the most commonly used and accepted in the furnace industry being the PID, or Proportional-Integral-Derivative, control.

“This popular controller is used because of its robust performance in a wide range of operating conditions and simplicity of function once understood by the processing operator,” writes Real J. Fradette, a Senior Technical Consultant with Solar Atmospheres, Inc, and the author of “Understanding PID Temperature Control as Applied to Vacuum Furnace Performance” (with William R. Jones, CEO, Solar Atmospheres, Inc, contributing).

The PID algorithm consists of three basic components, Proportional, Integral, and Derivative which are varied to get optimal response. If we were to observe the temperature of the furnace during a heating cycle it would be rare to find the temperature reading to be exactly at set point temperature. The temperature would vary above and below the set point most of the time. What we are concerned about is the rate and amount of variation. This is where PID is applied. ~ Fradette

In this week’s Technical Tuesday, we direct our readers to Fradette’s article at Solar Manufacturing’s website where he and Jones cover the following on PID temperature controllers:

• Definitions, e.g., Closed Loop System; Proportional (GAIN); Integral (RESET); and Derivative (RATE)
• Actual operation of a PID temperature controller, including understanding PID dimensions and values; and general rules for manually adjusting PID
• The art of tuning, a manual
• Autotuning
• Tweaking the furnace PID controller
• and other factors