A digitally programmable temperature controller based on phase-lock loop

A digitally programmable temperature controller based on the phase-lock loop is described. The temperature is sensed in frequency form and compared with the reference frequency corresponding to the target temperature in a phase detector in order to derive the actuator. The frequency difference is also detected by a one-chip microcomputer which changes the reference frequency according to the proportional-integral-derivative operation. A prototype controller achieved 0.1 degrees C accuracy in temperature control of a water bath.<>