10 years ago.

Vibrating Wire Sensor

Good Evening,

I'm after a bit of advice trying to read the output of a vibrating sensor (http://www.mgs.co.uk/data/pdf/65.pdf)

The idea of this type of sensor is that is it firmly attached to a material and changes in strain are measured by means of a vibrating wire. As the strain changes the resonant frequency also changes and gives an accurate representation of the change in strain.

My circuit is as follows:

Mbed PWM pin and digital out connected to a H bridge input (digital out held low). The coil is then subjected to a frequency sweep and then the outputs are switched off. Across the coil is also an instrument amp configured with a high gain.

The problem....

The coil is excited correctly as we can hear the harmonics of the vibrating wire within the sensor, however, we don't get any signal from the sensor when the pulses are removed.

We can see the pulses are ok, and we also see a good output on the amp! But nothing that could be used determine the resonant frequency, and therefore the strain. I currently have a NI data acquisition unit attached to the output of both the PWM and opamp for diagnostic of the analog signals.

Any suggestions would be greatly received!