Calculating Coherence for Structural Durability Testing
|Publication Date:||1 September 2018|
This procedure explains when coherence could be used in a project, how to calculate it, and some guidelines in interpreting coherence results.
Coherence is used to estimate the likelihood that a given drive signal, when used as input into a given system, causes the given response signal. This procedure is applicable for digital time histories in Remote Parameter Control (RPC) format when one set of channels is identified as drive channels and one set is identified as response channels. Traditionally, the drive channels have been rig drive channels, and the response channels are remote parameter channels, however, a method is available to calculate pseudo-coherence selecting some channels as pseudo-drives and some as pseudo-responses. Appendix A, Figure A1 illustrates the traditional process for calculating coherence using RPCpro software. Any automated tool must comprehend all processing steps shown, plus optional steps necessary for calculating pseudo-coherence. These optional steps for pseudo-coherence in an RPCpro environment include extracting both the Response and Drive channels. The drive and response files must have the same length of time, same sample rate, and same frame size. There does not need to be the same number of drive and response channels.