The Geotechnical Laboratory at Virginia Tec has a Resonant Column manufactured by GDS. The GDS Resonant Column Apparatus (GDSRCA) is a true fixed free resonant column where one end of a confined solid or hollow cylindrical soil specimen is excited and the other is fixed. From the resonant frequency, small strain stiffness can be found.
- RCA systems that GDS supplies are current driven using a transconductance power amplifier: This is because the impedance of magnet / coil devices change with frequency. At higher frequencies, using a constant voltage amplifier the current would be seen to reduce. As the torque is directly proportional to current, the torque will also reduce and a non-linear torque input would affect results. This effect is removed in the GDSRCA by using a current driven power amplifier.
- Designed to provide maximum rigidity: Providing minimum losses and a more consistent frequency response and no rigid support to the top cap so it is completely free vibrating.
- Dedicated GDS RCA software is used for control and data acquisition of the RCA apparatus: Simple automated tests.
- Low equipment damping: The software switches the hardware to provide an ‘open circuit’ through the coils during free vibration decay, which prevents ‘back’ EMF generation and reduces equipment damping effects.
- Electro-magnetic drive system: Which incorporates precision wound coils and composite sintered neodymium iron boron (NdFeB) “rare-earth” magnets.
- Internally mounted, counter-balanced accelerometer: Used to measure vibratory response of the sample.
- Internal cell: To surround sample with water, to avoid air penetrating the membrane.
More information about this device can be found here.