Is your vibration controller squaring with Chi?
A random spectrum generated by a Vibration Research controller without iDOFTM looks jagged due to proper statistical performance. For any random test, the measured amplitude of every g2/Hz PSD spectral line of the control signal should be governed by predictable (± dB) confidence limits derived from the chi-squared (χ2) distribution.
In the case study, “Does Your Controller Square with Chi?“, several testing methods show undesirable statistical behavior. We found that some commercial random controllers use more than the number of DOF specified in the setup parameters for PSD calculation. This error gives the appearance of a tighter ±dB match between the Demand and Control spectra than both theory and the operator-entered DOF support. Other controllers show evidence of non-Gaussian signal behavior.
The Chi-Squared Distribution Calculator provided by Vibration Research performs a statistical analysis of your controller. The comprehensive spreadsheet exports the Demand and Control spectra to Microsoft Excel® and is compatible with any controller. This free calculator is a simple alternative if:
- Your controller cannot perform χ2 calculations
- You do not own the optional software to implement embedded calculators
- You are not comfortable programming a similar data transfer and investigation
Chi-Squared Distribution Calculator (Excel)