Earlier this year we released the AVW200-series, which is our new vibrating-wire interface.  You can go to our website at for more information about the AVW200 .  The quality of measurement for the sensors is far superior to the previous method and the noise sensitivity for these types of measurements is almost completely eliminated.

Please recognize that the AVW200 replaces the AVW1, AVW4 and AVW100. We are encouraging everyone to use the AVW200-series when they order new interfaces since they provide the best possible data measurement for vibrating wire (VW) sensors.

OLD:  Until now, most VW sensors’ output readings were determined by measuring the time period required for a user-specified number of cycles (usually 200 to 500).   This measurement technique is susceptible to external noise.  If the noise amplitude was within the range of the comparator’s measurement capabilities, the noise cycles would be averaged in with the resonant frequency cycles, leading to erroneous results. This is even more pointed for VW sensors whose signals have lower frequencies and amplitudes.  (Some have signal amplitudes lower than 1 mV rms, which is below the level of some instruments’ comparator capabilities.)   This lack of measurement integrity has been a concern for many of CSI's customers and led CSI to investigate a new approach that uses spectral analysis to determine the wire's resonant frequency. This method improves noise immunity and allows for the measurement of lower-level signals.

NEW:  The new approach (1) records the time-sampled response of the VW sensor using an analog-to-digital converter, (2) transforms the time response to a frequency spectrum, and (3) interpolates the spectrum to determine the wire’s resonant frequency.  In the past it was deemed that, due to the large amount of measurement and processing time required for a Fourier transform to resolve the required frequency resolution, Fourier analysis could not be used for VW measurements.  The new approach, with its interpolation scheme, solves this dilemma. The newly designed AVW200 interface excites the VW sensor, measures the response, performs a Fourier transform on the response, and returns the result with a resolution better than 0.001 Hz, all within two seconds. Because spectral analysis can distinguish signal from noise on the basis of frequency content, this technique offers improved immunity to competing noise.  In a typical noise benchmark, spectral-analysis frequency errors are less than ±0.02 percent of the reading. Compare this to frequency errors exceeding 100 percent of the reading using traditional time-domain methods.  Spectral analysis also offers improved precision during quiet conditions, achieving a frequency precision of better than 1x10^-3 Hz rms. 

Note: You don’t have to replace your existing AVW interfaces, and CSI will continue to support and repair them.  We will be discontinuing the legacy AVW interfaces by 31 Dec 2008.  They have already been removed from our price list, and we have limited quantities for sale.  If you have any questions, please contact one of our Application Engineers at sales@csafrica.co.za.