EN 13477-2-2011 pdf download.Non-destructive testing – Acoustic emission – Equipment characterisation – Part 2: Verification of operating characteristic.
The characterisation of the AE signal processor shall be performed using simulated burst signal parameters in a range covering the equipment specification. The recommended test signal patterns’ frequency, dynamic range and acceptable inaccuracy of each measurement is given in the corresponding clause of this standard and summarized in Table 3. Less accurate test signal generators can be used, if the inaccuracy of each pattern is measured and considered during verification.
The test signal frequency shall always be within the bandwidth of the measurement chain. Only the verification of the bandpass filter characteristics needs frequencies outside of the nominal bandwidth. If a filter is changed, the gain shall be checked and adjusted accordingly.
Before proceeding to verify the measured AE parameters, the bandwidth, detection threshold and AE signal processor noise shall be checked.
7.2 Bandwidth and filter roll-off verification
Bandwidth verification of the AE signal processor has to be performed as described In 6.3.3 for the peamplifier. The results I, HP roll-off, and F1,p, LP roll-off shall be reported according to the example in Annex and compliance with the acceptance limits checked (see Annex C).
7.3 Detection threshold verification
The detection threshold setting may be either fixed with variable gain, variable with fixed gain or floating at a fixed relation to the background noise.
The test set-up is shown in Figure 12. A triangle modulated sine wave with at least 20 cycles rise and 20 cycles decay time, or a sin2-modulated sinewave with at least 40 sine waves per burst shall be used.
Threshold test values of 40 dBAE and 70 dB shall be verified.
The amplitude of the test signal shall be varied until approximately 50 % of the test signals are detected by the
AE signal processor. The obtained test signal amplitude represents the actual detection threshold setting.
The acceptable threshold inaccuracy is equal to the acceptable peak amplitude inaccuracy ± 1 dB.
For floating threshold, if applicable, the manufacturer shall provide details about verification and acceptance limits.
7.4 AE signal processor noise verification
All three main components, AE sensor, AE preamplifier and AE signal processor, contribute to the total noise of a measurement chain. The AE signal processor noise defines the minimum threshold without getting false hits, while no preamplifier is connected. It is important that increased AE signal processor noise is observed in order to avoid noise contaminated data or the need of a threshold increase above the level foreseen by an applicable test instruction.
— input termination used, (e.g. high impedance or 50 Ohm);
— bandpass filter(s) used;
— time window ( 1 second) and sampling rate for determination of peak noise and, if applicable. RMS noise.
For the verification of AE signal processor noise, no preamplifier shall be connected. Either the peak noise has to be determined by searching the lowest threshold level that causes less than one hit per second, or the peak noise has to be taken from a seamless waveform record of at least one second duration. The determined noise level shall be reported as peak value in jtV and optionally as RMS value in pV with reference to the measurement range of the preamplifier input, usually ± 100 mV. The peak noise can be converted from iV to dB. An example of a report form is shown in Annex C.
7.5 Burst signal parameter verification
7.5.1 General
This section gives the procedure for verifying the measured AE burst signal parameters. The test parameters. test signal, required tests and minimum acceptance limits are given in this clause. Acceptance limits derived from the manufacturer’s specifications may be tighter. The range of test signals used shall properly cover the dynamic range of all verified burst signal parameters.
For the verification of energy counts and duration, by using a rectangular modulated sine wave, the signal behind the application specific filter may exhibit additional ring down counts at the end of the signal. An example is shown in Figure 13. The effect of those additional ring down counts on the readings of energy, counts and duration can be compensated: an additional reference measurement of short duration is used to determine an offset value for each of the results energy, counts and duration, which should be constant for all durations. Accordingly, all other measurement values of a test series of vaned duration can be corrected by considering the determined offset values.EN 13477-2-2011 pdf download.