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
GB/T 39849-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S 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’s 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 Ω and 75 Ω,
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 Ω. 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 Δf (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 Hert...