Using an oscilloscope for calibration and verification purposes, we measured the initial voltage V0=448mV
from Figure 5(a), at time location t0. From Figure 5(b), we measured reflected voltages V1=30.4mV at time location
t1 and V2=70.4mV at time location t2. We measured t1=6.76μs from Figure 5(a-b), and from Figure 5(b) we
measured t2= 1.440μs. Knowing the actual thickness of steel=19.50mm and tungsten=3.85mm, we calibrated for
1=5769m/s and 2=5347m/s using equation (4) and measured t1 and t2 from the oscilloscope. Our measurement
results of 1=5769m/s and 2=5347m/s for steel and tungsten closely match the values found in [2] (i.e. 1=5890
m/s, 2=5180 m/s), such that the slight difference is due to the manufacturing process of the two metals. Using
equations (12) and (15) we calculated signal losses in the two mediums 1=1.59dB/cm, and 2=9.46dB/cm. Thus,
the total signal loss through the two mediums is 13.4dB for one echo reflection. Another 16.5dB is required to bring
the 448mV to a rail-to-rail voltage swing of 3.0V; thus, a minimum gain of approximately 30dB was needed. Since
other factors in the NDT-module design will contribute to the echo signal loss, such as the Muxes, two BPFs, DET,
and LPF, the digitally controlled PA compensates for approximately 15dB of dynamic range.
Using an oscilloscope for calibration and verification purposes, we measured the initial voltage V0=448mV
from Figure 5(a), at time location t0. From Figure 5(b), we measured reflected voltages V1=30.4mV at time location
t1 and V2=70.4mV at time location t2. We measured t1=6.76μs from Figure 5(a-b), and from Figure 5(b) we
measured t2= 1.440μs. Knowing the actual thickness of steel=19.50mm and tungsten=3.85mm, we calibrated for
1=5769m/s and 2=5347m/s using equation (4) and measured t1 and t2 from the oscilloscope. Our measurement
results of 1=5769m/s and 2=5347m/s for steel and tungsten closely match the values found in [2] (i.e. 1=5890
m/s, 2=5180 m/s), such that the slight difference is due to the manufacturing process of the two metals. Using
สมการ ( 12 ) และ ( 15 ) เราคำนวณสัญญาณจากสองสื่อ 1 = 1.59db/cm และ 2 = 9.46db/cm . ดังนั้น
รวมการสูญเสียสัญญาณผ่าน 2 สื่อ 13.4db หนึ่งก้องสะท้อน 16.5db อื่นต้องเอา
448mv ไปยังรถไฟรางแรงดันสวิงของ 3.0v ดังนั้น กำไรขั้นต่ำประมาณ 30db เป็นที่ต้องการ ตั้งแต่
other factors in the NDT-module design will contribute to the echo signal loss, such as the Muxes, two BPFs, DET,
and LPF, the digitally controlled PA compensates for approximately 15dB of dynamic range.
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