Operating Deflection Shapes: Extracting ODS from Cross Channel Phase Data

The information provided is for help with Commtest Instruments products:

• vb3000 instrument

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QUESTION

How do I obtain an operating deflection shape from cross channel phase data?

ANSWER

You can enter the raw data points into a spreadsheet program such as Microsoft® Excel, perform a few calculations, then plot the results as an operating shape chart. This procedure is described below.

Setup

This example uses 12 roving readings away from the reference point. You can download this spreadsheet, which includes the example data, the calculations, and the resulting plot.

Measurement	Reference	Roving	Phase
1	0.1148	0.2183	40
2	0.1149	0.1891	135
3	0.1151	0.1787	330
4	0.1147	0.2378	180
5	0.1152	0.2177	220
6	0.1151	0.2989	315
7	0.1147	0.2288	1
8	0.1156	0.1278	125
9	0.1152	0.1676	215
10	0.1149	0.1377	230
11	0.1145	0.1879	140
12	0.1145	0.2481	215

1. Take the raw data across a machine member.
2. Normalize the data by taking the ratio of the Roving/Reference data and multiplying the resulting number by the average Reference value.
3. Pick the point of highest amplitude (#6).
4. Re-reference all phase angles to this point (315 degrees).
5. Take the normalized amplitudes and multiply them by the Cosine of the re-referenced phase angle.
6. Plot the results.

The resulting plot then shows the shape, with the peak deflection being at the point with highest amplitude.

FAQ ID: 18012 Last Reviewed: 3 October 2006