The use of control theory for the design of voltage clamp systems: a simple and standardized procedure for evaluating system parameters.

Voltage clamp (VC) instruments are closed-loop control systems based on electronic feedback. Such feedback systems can be described in the framework of control theory. We used a mathematical approach based on control theory to improve the performance of VC systems. This approach considerably simplifies the design and optimal tuning of these systems, as is demonstrated for a standard two electrode and a time-sharing single electrode clamp system. The major advantage of this approach and the consequent optimization procedure is that only proportional-integral controllers for VC systems must be used. As a consequence, the design of such VC systems is solely based on the time constants of the clamp circuit. In our approach, the 'symmetrical optimum' rule was applied for the first time to VC systems. This yields optimized systems with respect to speed of response and clamp accuracy. An empirical procedure has been derived from this theoretical approach which allows the optimal tuning of VC instruments based on PI controllers while running an experiment.