CDM-VW300

The CDM-VW300 is a two-channel interface that you can use between standard single-coil circuit vibrating wire sensors and data loggers to allow shorter intervals between measurements. With the CDM-VW300 interface, you can achieve much faster and better measurements without having to purchase new sensors. Sensors typically used with the CDM-VW300 are strain gages, load cells, pressure transducers, crackmeters, and tiltmeters. 

This interface uses an excitation mechanism that maintains the vibrating wire sensor in a continuously vibrating state. The interface measures the resonant frequency of the wire between excitations using the patented vibrating wire spectral-analysis technology (VSPECT™). VSPECT provides very fine measurement resolution and also limits the influence of external noise by discriminating between signal and noise based on frequency content. Because of this technology, the signal can be carried through longer cables, giving you flexibility in your sensor and data logger siting.

You can connect multiple CDM-VW300 modules to one data logger. The CDM-VW305 is similar to this item, but it has eight channels.

The dynamic vibrating wire measurement technique is protected under U.S. Patent No. 8,671,758, and the vibrating wire spectral-analysis technology (VSPECT) is protected under U.S. Patent No. 7,779,690.

In addition to the dynamic vibrating wire measurement, the CDM-VW300 makes several auxiliary measurements. A static vibrating wire measurement is made once each second, along with the dynamic measurements, which provides finer measurement resolution and greater immunity to external noise sources. The CDM-VW300 includes a thermistor input channel paired with each vibrating wire channel, featuring high-precision 24-bit measurements at a 1 Hz rate. Lastly, a rich set of diagnostic parameters is provided with the vibrating wire data.

The CDM-VW300 has the capability to simplify post-processing of data by computing common values internally. Vibrating wire data can be reported as measured frequency or as the frequency squared with a multiplier and offset applied. The thermistor data is reported as resistance or is converted to degrees Celsius using the thermistor’s Steinhart-Hart coefficients. The CDM-VW300 also can internally compile rainflow histograms from the final data and report the values at user-specified intervals.

Vibrating Wire Inputs

Each channel has two terminals for connecting to the coil of the vibrating wire sensor. Both vibrating wire terminals are labeled VW and the polarity of the wiring is arbitrary. The sensor is excited and measured through the same connections. Sinusoidal excitation is applied for a few cycles of the wire oscillation. The wire is maintained in a continuously vibrating state. Excitation voltage varies automatically to maintain the desired return signal strength.

Thermistor Inputs

Each channel has two terminals for connecting to the thermistor. Both thermistor terminals are labeled T and the polarity of the wiring is arbitrary. The measurement is a half-bridge configuration with the excitation circuitry and completion resistor integrated into the module.