A wireless telemetry system for strain measurement

A new strain measurement using wireless telemetry technique in civil engineering applications is proposed. The technique makes use of a transponder together with a strain gauge. The transponder is powered by the inductive coupling method which eliminates the need for expensive cable runs in the concrete for conventional strain measurement. The measured strain data is digitized and sent back to the PC-controlled reader using frequency shift keying (FSK) at two discrete frequencies of 134.2 kHz and 123.2 kHz. A prototype was built using commercial micropower CMOS ICs to verify its functionality. Measurements from the prototype have achieved a 100 cm reading range without any trimming on the capacitors in the resonance circuit. The total current consumption of the complete wireless strain measurement system was merely of 100 μA for 1000 Ω resistance stain gauge