Vibrating wire (VW) devices sense strain in a pre-tensioned wire. The fundamental frequency of wire oscillation is a function of tension in the wire, like a guitar string. The transducer is constructed so that the physical parameter being measured influences the strain or tension in the wire, and therefore the fundamental frequency at which it vibrates. VW devices are used in many strain and pressure gauges employed in
geotechnical and structural instrumentation.
The Model 1211 VWT Input Assembly is designed to measure a single VW gauge of the type that can be excited by a momentary electrical pluck or chirp signal driving an electromagnetic coil to exert forces on the wire. After the wire is excited, the fundamental frequency of oscillation induces a signal into the same coil, which is measured on the same pair of signal wires used for excitation. The 1211 VWT also provides a second channel to measure the resistance of a thermistor temperature sensor, which is often built into VW instruments. The temperature of the gauge is normally used to compensate for a temperature coefficient of the measured parameter, but is sometimes used to record groundwater temperature changes for depth/level pressure transducers or piezometers.