A Proposal of New CST Method for Carrier Type Dynamic Strain Amplifier with C Component on 4 Arms of Bridge

Abstract

Carrier type dynamic strain amplifiers are frequently used for stress measurement with strain gages. That is because the carrier type dynamic strain amplifier can conduct high precision measurement since it is highly resistant to external noise or power noise in the field. The strain gage has little effect on specimen being measured since it is small and light weight. However it is required to connect the input cable from the target strain gage to the amplifier. In case of using the carrier type dynamic amplifier, distributed capacitance due to the input cable greatly effects zero point variation.
The distributed capacitance changing degrades the stability of the dynamic strain amplifier.
We made up and logically clarify Dual Feedback CST (Capacitance Self Tracing) method that detects, self-tracks and eliminates the capacitive component generated in any arm of the measuring bridge. The zero-point variation is not affected by the carrier frequency and resistance value and can be cancelled if the bridge is balanced in the CST method.
We conducted experiments with strain gage resistance 120 ohm or 350 ohm and carrier frequency 5 kHz, 12 kHz or 28 kHz and verified the zero-point stability.