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GB/T 39849-2021 English PDF (GBT39849-2021)

GB/T 39849-2021 English PDF (GBT39849-2021)

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GB/T 39849-2021: Non-destructive testing instruments -- Ultrasonic time-of-flight diffraction instrument -- Methods of performance tests

This Standard specifies methods of performance tests for the UTOFD instrument. This Standard applies to the UTOFD instrument.
GB/T 39849-2021
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 19.100
N 77
Non-destructive testing instruments - Ultrasonic time-
of-flight diffraction instrument - Methods of
performance tests
ISSUED ON: MARCH 09, 2021
IMPLEMENTED ON: APRIL 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the PEOPLE Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Test method ... 6
Non-destructive testing instruments - Ultrasonic time-
of-flight diffraction instrument - Methods of
performance tests
1 Scope
This Standard specifies methods of performance tests for the UTOFD
instrument.
This Standard applies to the UTOFD instrument.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only the dated version applies to this document. For undated references, the latest edition (including all amendments) applies to this document.
GB/T 12604.1, Non-destructive testing - Terminology - Terms used in
ultrasonic testing
3 Terms and definitions
Terms and definitions determined by GB/T 12604.1 and the following ones are applicable to this document.
3.1 Sampling rate
The number of samples that are collected in unit time when analog-to-digital conversion is performed on an analog signal.
Note: The sampling rate unit is equivalent to the frequency unit Hertz (Hz). 3.2 Ultrasonic time-of-flight diffraction; UTOFD
The propagation time of the ultrasonic diffraction.
3.3 UTOFD instrument
UTOFD instrument
When the UTOFD instrument is placed in the double crystal probe working mode (transmitter and receiver are separated), the amount of energy leakage suppression from the output of the transmitter to the input of the receiver during the transmission of the transmitted pulse.
4 Test method
4.1 Test conditions
The UTOFD instrument shall be tested under the following conditions:
a) The ambient temperature is 20 ??C ?? 5 ??C;
b) The relative humidity is 45% ~ 75%;
c) The AC power supply voltage is 220 V, and the error is ??2%;
d) The AC power supply frequency is 50 Hz, and the error is ??1 Hz;
e) The error of the DC power supply voltage is ??1% of the rated value;
f) Avoid external electromagnetic field interference;
g) The ventilation is good;
h) Avoid direct sunlight.
4.2 Instruments and equipment
The performance and stability of the used electronic equipment shall meet the testing requirements. Use the following main instruments and equipment: a) An oscilloscope whose bandwidth is not less than 100 MHz.
b) A non-inductive resistance whose resistance values are 50 ?? and 75 ??, and maximum allowable relative error is ??1%.
c) A standard attenuator, of which the step is 1 dB, the total attenuation is 100 dB, and the output impedance is 50 ??. When the signal frequency is
within 15 MHz, the cumulative error within the range of any 10 dB shall be within ??0.3 dB.
d) Choose one of the following two generators:
1) An arbitrary waveform generator;
2) Two pulse signal generators, which are equipped with external trigger or gate, to output two gated sinusoidal radio frequency signal strings. 4.3 Performance test
4.3.1 Frequency bandwidth
According to the connection mode that is shown in Figure 2, connect the input signal to the receiving end of the UTOFD instrument, and set it to dual-probe working. Calibrate the attenuator. Adjust the input signal of the ultrasonic instrument to reach ??1 V peak-to-peak value.
Select each working frequency band in turn; measure their respective
frequency bandwidths respectively. For each selected working frequency band, change the frequency of the input signal in the range of 0.1 MHz ~ 25 MHz; observe the output of the UTOFD instrument. Search the frequency when the output of the UTOFD instrument reaches the maximum. When searching, the attenuator shall be adjusted at the same time, so that the output signal amplitude that is displayed by the UTOFD instrument does not overflow the screen. Check the oscilloscope at any time, to confirm from the display on the oscilloscope that the input signal amplitude remains constant. When the output of the UTOFD instrument reaches the maximum frequency fmax, adjust the
attenuator to make the display amplitude reach 80% of the full-screen amplitude of the UTOFD instrument. Record this frequency fmax and the value of the attenuator.
Reduce the attenuator value by 3 dB. Respectively increase and decrease the frequency from fmax, in turn, in an increment that is 5% less than the nominal frequency bandwidth; observe the signal that is displayed by the UTOFD
instrument. When it returns to 80% of the full-screen amplitude, respectively record the corresponding upper-limit frequency value fu and the lower-limit frequency value fl (-3 dB point). Confirm again that the input signal is constant. The center frequency fo of the working frequency band is calculated according to Formula (1):
Where:
fo ?€? center frequency, in Hertz (Hz);
fu ?€? upper-limit frequency, in Hertz (Hz);
fl ?€? lower-limit frequency, in Hertz (Hz).
The frequency bandwidth ??f (between the -3dB point) of the working frequency band is calculated according to Formula (2):
If the noise level is greater than 5% of the full-screen amplitude, reduce the gain, until the noise level is 5% of the full-screen amplitude. Adjust the input signal amplitude, so that the signal amplitude that is displayed by the UTOFD
instrument reaches 10% of the full-screen amplitude of the UTOFD instrument. Use the oscilloscope to measure the voltage Vmin of the input signal (consider the setting of the external standard attenuator when measuring; generally, set to 40 dB ~ 50 dB); record the gain value.
If the gated signal generator cannot provide a sufficiently low voltage, reset the UTOFD instrument to a level of 20 dB greater than the minimum gain; make necessary corrections to the measurement results.
The dynamic range is calculated according to Formula (3):
Where:
GD ?€? dynamic range, in decibels (dB);
Vmax ?€? voltage of the input signal, in volts (V);
Vmin ?€? voltage of the input signal, in volts (V).
If Vmin is lower than the equivalent input noise Vein, the dynamic range GD is calculated according to Formula (4):
Where:
GD ?€? dynamic range, in decibels (dB);
Vmax ?€? voltage of the input signal, in volts (V);
Vein ?€? equivalent input noise, in volts (V).
4.3.3 Time base linearity error
Provide 11 equally spaced sine wave pulse trains through the signal generator; compare them with the scale value corresponding to the position of each signal that is indicated on the time base line of the UTOFD instrument; measure the time base linearity of the UTOFD instrument.
Use the instrument configuration that is shown in Figure 2, to generate a sine wave pulse train detection signal that has 11 equidistant intervals, as shown in Calculate the noise per square root bandwidth according to Formula (6): Where:
Vein ?€? equivalent input noise, in volts (V);
Vin ?€? peak-to-peak voltage of the input signal, in volts (V);
S ?€? attenuation of the calibrated external attenuator, in decibels (dB); nin ?€? noise per square root bandwidth, in volts every one-half square hertz (V/H 1/2
z );
fu ?€? upper-limit frequency, in Hertz (Hz);
fl ?€? lower-limit frequency, in Hertz (Hz).
For the measurement method of fl and fu, see 4.3.1.
4.3.6 Transmitted pulse voltage amplitude, transmitted pulse rise time, transmitted pulse duration, transmitted pulse recoil amplitude
Put the UTOFD instrument in the double crystal probe working mode; connect the oscilloscope to the transmitting end of the UTOFD instrument.
Set the pulse repetition frequency to the maximum; connect a 50 ?? non-
inductive resistance to the transmitter output socket. Use the oscilloscope to measure the transmitted pulse voltage V50. As shown in Figure 5, measure the transmitted pulse rise time tr, the transmitted pulse duration td and the transmitted pulse recoil amplitude Vr.
Repeat the measurement at each emission intensity set value and/or pulse frequency set value, maximum and minimum damping gears.
Repeatedly measure the minimum pulse repetition frequency of the clear
waveform that is displayed on the oscilloscope screen.
Ds ?€? cross-talk damping during transmission, in decibels (dB);
V50 ?€? peak-to-peak voltage of the output end, in volts (V);
VE ?€? peak-to-peak voltage of the receiving input end, in volts (V).
4.3.8 Transmitted pulse repetition frequency
Put the UTOFD instrument in the double crystal probe working mode; connect the oscilloscope to the transmitting end of the UTOFD instrument.
Under each set value of different pulse repetition frequencies, use the oscilloscope to measure the repetition frequency of the transmitted pulse. If the controller of the UTOFD instrument has multiple combined gears, and the pulse repetition frequency (usually the range and pulse repetition frequency) of the combined gears is the same, only one of the combined gears needs to be
detected. For the UTOFD instrument that is equipped with a continuously adjustable controller of pulse repetition frequency, a set value shall be selected for testing from the product technical requirements that are given by the manufacturer.
4.3.9 UTOFD instrument sampling rate
Measuring instruments: arbitrary waveform signal generator (the highest output frequency is greater than 1/4 of the UTOFD instrument sampling rate),
attenuator, 200 MHz digital oscilloscope, general-purpose computer. The computer is equipped with waveform analysis software including sawtooth waveform analysis.
Connect the output of the arbitrary waveform signal generator to the input end (probe interface) of the receiving circuit of the measured UTOFD instrument through the attenuator; connect the output end of the measured UTOFD
instrument to the input end of the digital oscilloscope; output the digital signal of the UTOFD instrument to the computer. If the UTOFD instrument sampling rate is adjustable, the UTOFD instrument sampling rate indication shall be adjusted to the maximum sampling rate.
Set the arbitrary waveform signal generator to output sawtooth wave; place the output amplitude in the appropriate gear; the period is appropriately selected according to the highest real-time sampling rate that is given in the product specification of the UTOFD instrument. Adjust the amplification rate of the attenuator and the UTOFD instrument, so that the output waveform of the UTOFD instrument that is output to the personal computer has an appropriate value, which is large enough and does not exceed the maximum limit. Adjust the oscilloscope to display a sawtooth signal of more than one period; the vertical amplitude occupies about 80% of the screen.
measured UTOFD instrument; connect the input end of the digital oscilloscope to the output end of the measured UTOFD instrument.
Adjust the sine wave signal generator to output a sine wave whose period is T. Adjust the window adjustment of the measured UTOFD instrument; observe the measured windows length.
4.3.13 Sampling error
It is used to test whether the signal corresponding to the highest frequency within its bandwidth of the UTOFD instrument can be correctly displayed on the display screen, especially whether the signal amplitude has nothing to do with the time base line range.
The detection should be carried out in the detection and radio frequency modes of each frequency band; the time-dependent gain curve should not be used. This test should be repeatedly carried out for each set value that affects the number (such as time base range and pulse repetition frequency).
Set the UTOFD instrument in the double crystal probe working mode; adopt the device configuration that is shown in Figure 2 to generate a detection signal that is synchronized with the transmitted pulse. Adjust the signal delay T to T0, so that T0 is greater than the dead zone after the transmitted pulse. Adjust the frequency of the gated RF signal generator to the upper-limit frequency fu of the corresponding frequency band; adjust the signal generator, so that it outputs a single-cycle sine wave signal whose amplitude is 80% of the full-screen amplitude.
Use variable delay; when the delay T is increased by a small increment ??T, the increment ??T is calculated according to Formula (9).
Where:
??T ?€? time increment, in seconds (s);
fu ?€? upper-limit frequency, in Hertz (Hz).
Each time ??T is increased, measure the signal amplitude that is displayed on the display screen. Continue to increase the time delay and measure the signal amplitude, until 30 measurements (that is, 3 wavelengths) are completed. 4.3.14 Response time

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