Investigation of Signal Conditioning for Tx-Rx PEC Probe at High Lift-Off Using a Modified Maxwell’s Bridge

Abstract

Pulsed eddy current testing is widely used because of its richness in spectral components. However, the degrading sensitivity as lift-off increases poses a challenge to its application in thick insulation or buried structures and weld areas. In the transmitter-receiver probe, self-impedance (offset) of receiver coil dominates the output signal, reducing the signal-to-noise ratio, especially at high lift-off. This limits the subsequent amplification of the output signal by the signal conditioning circuit. In practice, bridge-based measurements are used to mitigate this challenge but result in small linear range inputoutput characteristics. Electromagnetic interference and stray capacitance effects also cause measurement errors. This paper investigates a modified Maxwell's inductance bridge based on operational amplifier configuration for high lift-off testing. The receiver coil self-impedance is removed to improve signal-tonoise ratio and to make output signal proportional to impedance change only. Experiments are performed to evaluate the performance of the circuit in crack detection. The results show improved signal-to-noise ratio with maximum linearity deviation of 0.30%, and a higher crack detection sensitivity at 30mm high lift-off, in comparison to the conventional bridge circuit with maximum linearity deviation of 0.53%.

Design of differential probe with harmonic magnetic field and its data process method

“…3) Orthogonal phase-sensitive detection technique: First, two orthogonal reference signals are constructed for the target frequency f harmonic and denoted as (8) where f is the frequency of the target harmonic. The cross-correlation function between the differentialinduced voltage signal and the reference signals can be represented as…”

“…Differential sensors, as a design approach for probes, can effectively address this issue. Ona et al [8] have designed an improved pick-up coil structure by combining it with a Maxwell bridge as a magnetic field measurement sensor, further enhancing the probe's standoff distance. Zhang et al [9] have introduced a planar three-phase array probe, in which the output of the probe is only proportional to the size of the damage.…”

Investigation of rolling contact fatigue cracks using the transmitter-receiver eddy current testing under moving conditions

“…where 𝐿 , 𝐿 are the self-inductance of Tx and Rx, 𝑟 , 𝑟 are the internal resistance of Tx and Rx, 𝑙 , 𝑙 are self-coupling of Tx and Rx through the specimen, 𝑖 , 𝑖 are the current of Tx and Rx and 𝑀 is the indirect mutual inductance, and M is the direct mutual inductance that is negatively correlated with the distance (coil gap) between the driver coil and the pick-up coil. According to references [30,31] and equation (1), the 𝑉 is induced by the primary magnetic field and secondary magnetic fields, which are affected by the excitation current (𝑖 ), direct mutual inductance (M), and indirect mutual inductance (𝑀 . The secondary magnetic fields will change under moving conditions.…”

Electromagnetic Pigging System Based on Sandwich Differential Planar Coil

“…4. To ensure the same magnetic field, the excitation coil requires applying the same voltage, where it is placed parallel at both ends of the power supply [22][23][24] [25]. According to the Biot-Savart law, the magnetic flux relationship between the excitation and reception coils can be calculated, and Mutual inductance M can be solved by Neuman's formula [26] as…”