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A PID Temperature Controller

What's a PID controller? PID stands for "proportional integral differential" and relates to a process which seeks to continuously correct the error between a measured variable and a desired setting by calculating an appropriate correction process. In practice, it can largely avoid the large overshoots and undershoots that occur in simple temerature control systems.

By Leonid Lerner

Click for larger image

Keeping tight temperature control is essential in many processes. For instance, good temperature control of a PC board etching bath is essential for best results.

Too low a temperature and the process will be very slow, while too high a temperature will cause the etch resistant film to degrade and the solution to steam appreciably.

Another, arguably more important, process where precise temperature control is vital is in a good home brew!

Getting good temperature control is not as easy as it may seem. Consider the setup in in the photo at left and represented below in Fig.1.

When the hot plate is turned on, heat passes from the hotplate to the solution through the walls of the container.

When the temperature of the solution reaches the desired value, the controller (the Digital Thermometer/Thermostat featured in the August 2002 issue
of SILICON CHIP) switches the hot plate off but the temperature will continue to rise.

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