It is surprising that more than 30% of all factory PID control loops are operating in manual rather than automatic mode. To make matters worsewww.cechina.cn, of those loops operating in automatic modewww.cechina.cn, 65% produce less variance when in manual. This reality is possibly due to a dearth of personnel having sufficient know-how to tune and optimize a PID loop, which is one reason so many vendors provide automated configuration features. UnfortunatelyCONTROL ENGINEERING China版权所有, these are all not created equal, and utilities from various

vendors provide much different results. We will describe these features in the context of temperature control units, with the results of a performance comparison between several anonymous vendors.

　　Some controllers offer different degrees of aggressiveness in executing a set point change. Make your choice based on how fast the process needs to change against the product's ability to tolerate being overheated.
　　There are two levels of sophistication in this technologyCONTROL ENGINEERING China版权所有, commonly referred to as auto-tune and adaptive-tune (or continuous tune). Auto-tune is generally offered as a standard feature and relies on characterizing the system through artificial manipulation of control output power levels. however, this is generally impractical to do during production operation. The software watches the process and analyzes its response while applying either a step increase in fixed power level, or cycle-tune using oscillating power levels. The step-tune approach performs best when started from a stable, constant process. The cycletune is not as dependent on initial conditions控制工程网版权所有, but the process must be able to handle the amplitude of the necessary oscillations.
　　Adaptive-tune generally implies an increase in cost and requires more intelligence built into the controller. It must be able to monitor the process during production operation and judge when and how to modify PID parameters to maintain stability as conditions require. It characterizes the process without having to manipulate