GB/T 36668.2-2018Condition monitoring and fault diagnostics of amusement device—Part 2: Acoustic emission monitoring method (English PDF)

4.4 Interference factors

Before performing acoustic emission monitoring, it shall be aware of potential sources of noise, such as electronic noise (electromagnetic and radio frequency interference), airborne noise (air leakage or impact of grains of sand in a windy environment), operating background noise (fluid flow in the tube), and mechanical background noise. Their presence may affect the acoustic emission monitoring results.

8.1 General monitoring process specification

Organizations engaged in acoustic emission monitoring shall, in accordance with the requirements of this Part, develop general acoustic emission monitoring process specification. Its contents shall include at least the following elements.

a) scope of application;

b) referenced standards and regulations;

c) qualifications of implementers;

d) monitoring instruments and equipment. coupling agent, sensor, sensor fixture, signal line, preamplifier, cable, instrument host, monitoring data acquisition and analysis software, etc.;

e) information about the device and components being monitored. name, type, number, structural style, dimensions, installation location, design and operating parameters;

f) installation position and installation mode of sensor;

g) operating conditions and timing of monitoring;

h) sensitivity measurement;

i) monitoring process and data analysis and interpretation;

j) evaluation of monitoring results;

k) monitoring records, reports, and data archiving;

l) personnel of development, review, and approval;

m) date of development.

8.2 Monitoring work instruction or process card

For each monitored component or each set of monitored devices, in accordance with the requirements of 8.1, acoustic emission monitoring work instruction or process card shall be developed.

9.2 Baseline setting

Baseline data are mainly used to compare against subsequent measured values, to find changes in the monitored object. The determination of baseline data shall accurately specify the initial stable working conditions of amusement device. Baseline data shall be obtained under normal operating condition of the device. For the device with multiple operating conditions, a baseline shall be established for each condition.

For new and overhauled devices, changes in measured values during the first few days or weeks of operation are usually observed. Therefore, before baseline data are collected, run-in time shall be specified.

For device which has been running for a long time and is monitored for the first time, its baseline can be used as a reference point for device stabilizing.

9.3 Installation of sensor

The installation of sensor shall meet the following requirements.

a) According to the sensor installation position determined by the schematic diagram, install the sensor;

b) The installation position of sensor is surface-treated, to make the surface flat and expose the metallic luster. If the surface has a smooth and dense protective layer, it can be retained; but the attenuation of acoustic emission signal by the protective layer shall be measured;

c) Coupling agent is applied to the installation position of sensor. The coupling agent shall be made of materials with good acoustic coupling performance. It is recommended to use vacuum grease, vaseline, butter, and other materials. The use temperature class of the selected coupling agent shall be matched with the surface temperature of the piece under inspection;

d) PRESS the sensor at a certain installation position, so that the contact surface of the sensor and the installation position achieves a good acoustic coupling condition; […]

9.5 Monitoring implementation

9.5.1 Loading of monitored device

Under no-load conditions, the monitored device shall operate normally according to its operating mode. The operating time shall ensure that sufficient acoustic emission data is obtained.

Acoustic emission monitoring shall begin after the start-up operating speed of the device reaches the normal operating speed. Continuously MARK at least 10 operating cycles; and it shall ensure that the device is continuously operated for one week. If the device has different speeds, different steering, and other working conditions, it shall be tested separately under each working condition of the actual operation of the device.

9.5.2 Monitoring environment

Monitoring shall be carried out when environmental conditions permit. If there are factors affecting the monitoring results, they shall be excluded before monitoring.

During the monitoring process, it shall be noted that the following factors may generate noises which affect the monitoring results.

a) External mechanical vibration;

b) Movement or collision of components;

c) Electromagnetic interference;

d) Interference from wind, rain, hail, etc.;

e) Leakage of pneumatic and hydraulic components.

During the monitoring process, if strong noise interference occurs, it shall stop the operation and suspend monitoring; and then monitor after eliminating the strong noise interference.

9.5.3 Monitoring data acquisition and process observation

The monitoring data shall at least collect the parameters specified in Appendix A; and be able to acquire the acoustic emission signal waveform.

During monitoring, the change trend of acoustic emission RMS voltage and (or) energy over time shall be observed.

9.5.4 Monitoring data analysis

10.2 Result verification

If the monitoring result is rated at Grade I, no verification is required. If the monitoring results are all Grade I for several consecutive times, the monitoring cycle can be extended appropriately.

If the monitoring result is rated at Grade II, according to the use of the component under inspection, the monitoring cycle can be shortened.

If the monitoring result is rated at Grade III, the monitoring cycle shall be significantly shortened. According to actual conditions, the need for verification shall be determined.

If the monitoring result is rated at Grade IV, the operation of the device shall be stopped immediately; the rotating components shall be disassembled. Other testing methods shall be used for verification.

The verification of monitoring result grading shall, according to the testing methods specified in GB/T 34370.1~GB/T 34370.6, be carried out for surface and (or) internal defect testing.

11.1 Measurement interval

According to the age, operating condition, and the last monitoring results of device, the next monitoring time interval shall be determined. After the first monitoring, generally no more than 12 months, it shall be monitored again. The adjustment of measurement interval is used to grasp the signs of the occurrence of a fault and the deterioration speed and behavior of the expected fault, with the aim of accurately predicting the fault.

11.2 Acoustic emission signal interpretation

The primary purpose of data analysis is to correlate acoustic emission measurement results with operating condition, and to measure or monitor any deviations from the baseline, to help identify the condition of the device.

The criteria used to evaluate the operating condition of the device by acoustic emission include at least.

a) The strength of acoustic emission signal continues to increase over time;

b) Abnormal acoustic emission signal during steady operation;

c) At the fault repetition frequency, an amplitude modulated signal appears.

A.6 Filter

The frequency response of the filter placed in the preamplifier and system host processor shall match the frequency response of sensor.

A.7 System host

A.7.1 The acoustic emission system host shall have sufficient number of channels covering the inspection area. It shall at least display and store parameters of acoustic emission signal in real time (including arrival time, threshold, amplitude, ring-down count, energy, rise time, duration, number of impacts, RMS voltage). It shall have at least one channel for the acquisition of waveform. It shall have the function of receiving and recording external electrical signals such as load and temperature.

A.7.2 The independent sampling frequency of each channel shall not be lower than 10 times the frequency of the center point of sensor response frequency.

A.7.3 The threshold accuracy shall be controlled within ±1 dB.

A.7.4 The accuracy of count measured values of acoustic emission signal shall be within ±5%.

A.7.5 Within 10 s from the start of signal impact, the acoustic emission system, in the process of collecting, processing, recording, and displaying each channel, shall have the ability to process no less than 10 acoustic emission impact signals per second. When there is a large amount of data and a blockage occurs, the system shall be able to signal an alarm.

A.7.6 The accuracy of peak amplitude measured value shall be within ±2 dB.

At the same time, the dynamic range of the signal undistorted shall not be less than 65 dB.

A.7.7 The accuracy of the RMS voltage and energy measured values shall be within ±5%.

A.7.8 For the time difference positioning acoustic emission monitoring system, the resolution of rise time, duration, and arrival time of each channel shall be no more than 0.25 µs. The accuracy shall be within ±1 µs. The error between each channel shall be no more than ±3 µs of the average.

A.7.9 The accuracy of the voltage value of external parameters measured by the system shall not be less than 2% of the full scale. […]