Oscillation

Oscillation

A potentiostat is a specialized servo system. A servo system compares a measured quantity with a desired value. A negative feedback mechanism adjusts the system’s output until the measured quantity is equal to the desired setting. The term negative feedback is used because a positive perturbation in the measured quantity causes changes in the system output to drive the measured quantity negative.

In a potentiostat, the potential between the working and reference electrodes is the measured quantity. The potentiostat applies a voltage to the counter electrode to keep the measured voltage at a desired value.

Servo systems can become unstable. If the sign of the feedback ever becomes positive, perturbations in the measured quantity are magnified, not minimized. Positive feedback can cause wide, repeated swings in the system, known as oscillations. Often the oscillation swings all the way between the most positive and most negative system outputs. In most cases, the average value of these wide swings is not the same as the DC value the system would have without these oscillations.

Phase shifts in the feedback signal can cause a change in the sign of the feedback. Negative feedback phase shifted by 180° becomes positive feedback.

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Last revised on Thursday, August 30, 2007