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Typical Thickness Gage Adjustments

Pulser/receiver settings

The parameters in this section affect the excitation pulse sent to the transducer and the processing of returned echoes.

• Pulser energy: Permits selection of higher or lower excitation pulse energy. Higher energy optimizes penetration, while lower energy optimizes near surface resolution.

• Pulser frequency: Advanced gages utilize tuned pulsers that vary the frequency of the excitation pulse for optimum transducer performance.

• Receiver gain: Gages will typically operate with a default level of amplification applied to received echoes. Many gages permit user adjustment of gain to optimize response in applications involving very thin materials, thick or highly attenuating materials, or scattering materials. Automatic gain control is often employed to adjust echo height to an optimum level for detection and avoid saturated signals. Advanced gages will also incorporate time varied gain, which allows use of lower gain for thin measurements and higher gain for thick measurements, further optimizing echo detection over a broad thickness range.

• Rectification: Many waveform display gages permit display of received echoes as either an RF signal or a rectified signal (full wave or half wave). This can be an aid to echo interpretation in challenging applications.

Detection and timing settings

The parameters in this section determine which received echoes in a wave train will be detected and timed as the basis for thickness measurement.

• Measurement mode: Most gages will automatically select one of the measurement modes described in Section 3 as part of any default setup, however advanced users may wish to change the measurement mode to optimize performance, or choose the mode when beginning a custom setup.

• Echo window: This adjustment selects a time interval following the excitation pulse, corresponding to a thickness range in the test material, during which the gage will be able to receive echoes. Adjustment of echo window length can help prevent detection of noise and other spurious signals.

• Blanking: Echo blanking adjustments within the select echo window are a further tool to minimize the change of detection of noise, ringing, or other false signals in a wave train.

• Echo polarity: Permits section of the optimum lobe of unrectified echoes in situations where material acoustic impedance relationships cause inversions.

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Factors Affecting Measurement >>