Phase Inversion Detection

Multiple methods can be used to determine if a Phase Inversion occurs within a sample. Phase inversion can indicate a problem such as delamination within a part.

Phase Inversion with RTG Gates

RTG Gate with Phase Inversion detected

An RTG Gate runs an algorithm to determine if a Phase Inversion occurs. In summary, the gate checks that the following conditions are met:

• Absolute Peak Amplitude exceeds the Consider Threshold
• No Negative Peak is found or a negative peak occurs after the Positive Peak
• The Positive Peak crosses one or more Relative Threshold gates (the amplitude of which is determined by the absolute peak)

Note: RTG Gates are available in Hardware peak detection for 8xGTE A/D boards: for other devices, RTG Gates must be run with Software Peak Detection.

RTG Settings

An RTG Gate has the following settings:

1. Start
2. Length
3. Standard Threshold, any signal under the threshold is ignored. This behaves the same as any Data gate threshold.
4. Consider threshold, usually set above the standard threshold. Only if the APA exceeds this value will a Phase Inversion check occur.
5. Relative Thresholds, numbered 1-3, these are set at Percentages of the APA, not as absolute thresholds. Therefore, the "absolute" threshold of these gates will vary with the peak amplitude. There will be two positive and one negative relative thresholds.

Phase Inversion Algorithm

RTG Map superimposed on a Peak Amplitude Image.

To run a Phase Inversion check, the algorithm proceeds as follows:

1. did any signal exceed the standard Threshold? If not, stop.
2. record the APA, PPA, NPA, THPP, THNP values in the gate.
3. did the APA exceed the consider threshold? If not, stop.
4. Phase Inversion Check:
   1. adjust the relative thresholds based on the APA, e.g. if the APA is at 80% FSH, and the negative relative threshold is set for -60%, the "working" relative threshold is 80 * -0.6 = -48% FSH
   2. does a signal cross the negative relative threshold before crossing the positive relative threshold? If so, stop.
   3. If there is no negative signal crossing the negative relative threshold or it occurs after the positive relative threshold, check the postive relative thresholds.
   4. Does the positive peak cross one or more of the positive relative thresholds? Then record as phased inverted, with the intensity being the maximum relative threshold crossed.

On the image, this will result in a map that shows normal Peak data if no Phase Inversion is detected, or colors representing the intensity of the Phase Inversion. By default, those colors are Red (High) and Yellow (Low).

Phase Inversion using PCM

Standard PCM Palette.

The PCM method of determining Phase Inversion uses a combination of Signed Peak-to-Peak amplitude and a custom palette. Options allow the user to adjust the algorithm to use Peak Amplitude, order of peaks, or both to determine the value.

PCM can be used on any Data Gate. The Signed Peak-to-Peak amplitude feature must be enabled.

PCM Settings

The data Gate has the following settings:

1. Start
2. Length
3. Standard Threshold, any signal under the threshold is ignored. This is the normal Data gate threshold.
4. Consider threshold, usually set above the standard threshold: only if the APA exceeds this value will a Phase Inversion check occur)

The PCM Palette (shown at right) is colored so that high Phase inversion is 80% or above, and medium Phase Inversion is 60% or above.

Phase Inversion Algorithm

To detect Phase Inversion, the algorithm checks that the following conditions are met:

1. Checks that the absolute peak amplitude exceeds the Consider Threshold
2. (Peak Only): If the Negative peak exceeds the Positive Peak, record the Peak-to-Peak as phase inverted.
3. (Time Only): If the Negative peak occurs before the Positive Peak, record the Peak-to-Peak as phase inverted.
4. (Both): if the negative peak exceeds the positive peak and occurs before the positive peak, record the Peak-to-Peak as phase inverted.

On the image, the recorded values will reflect the Phase Inversion detected: normal values will be black and white, and samples that are Phase Inverted will be shown as yellow or red.