A new CST method for Carrier‐type dynamic strain amplifier with C component on four legs of bridge

AbstractCarrier‐type dynamic strain amplifiers are frequently used for stress measurement with strain gages. That is because the carrier‐type dynamic strain amplifier can perform high precision measurement since it is highly resistant to external noise or power noise in the field. The strain gage has little effect on the specimen being measured since it is small and light. However, it is required to connect the input cable from the target strain gage to the amplifier. When using the carrier‐type dynamic amplifier, distributed capacitance due to the input cable greatly affects zero point variation. Changes in the distributed capacitance degrade the stability of the dynamic strain amplifier.We present a new Dual Feedback CST (Capacitance Self Tracing) method that detects, self‐tracks, and eliminates the capacitive component generated in any leg of the measuring bridge. The zero‐point variation is not affected by the carrier frequency and resistance value and can be canceled if the bridge is balanced in the CST method. We conducted experiments with strain gage resistances of 120 and 350 ohms and carrier frequencies of 5, 12, and 28 kHz and verified the zero‐point stability. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(1): 11–18, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22294