Principles of CST Method
The CST (Capacitance Self Tracking) method is the KYOWA-developed method of electrically canceling any unbalanced capacitance constantly during measurement with the strain amplifier of AC bridge voltage system, automatically with no switch operation made. As shown in the block diagram below, the unbalanced capacitance detected by the C detecting circuit is inverted in phase by the drive and negation circuits. The inverted capacitance is added to the bridge output to negate the unbalanced capacitance. This method not only eliminates the need for troublesome initial adjustment of unbalanced capacitance of strain amplifiers using AC bridge voltage system but also cancels any unbalanced capacitance during measurement to solve the problem on unstable measurement due to unbalanced capacitance. It also enables use of higher-frequency AC bridge voltage and development of strain amplifiers featuring a frequency response at a maximum 10 kHz. Presently, all KYOWA strain amplifiers of AC bridge voltage system adopt the CST method.