Electro-magnetic noise

During initial periods, there were large number of spurious scram due to electro magnetic noise pickup by start up and delayed neutron detector channels and due to cross talk of fine impure test (FIT) pulse. Remedial measures viz., separation of signal cables from power cables, improvements in grounding system and reshaping FIT pulse were carried out and system performance improved. 

An optical fiber sensor is a new and an attractive AE sensor as alternative to the PZT sensor. It can ofier a number of advantages such as the longterm monitoring, the condition free from electro-magnetic noises, and the use of corrosive and elevated environments. One example applied to a pipe structure is illustrated in Fig. 3.14 (Cho, Arai et al. 2004). According to their results, the sensitivity depends on the number of fiber winding, and is still 10 times lower than a conventional PZT sensor. 

AE sensors transform surface motions into electric signals. Thus, the amplifiers are usually employed to magnify AE signals. Because cables from the sensor to the amplifier are subjected to electro-magnetic noise, specially coated cables of short length shall be used. Preamplifiers with sate-of-the-art transistors should be used to minimize the amount of electronic noise. Amplifiers with a flat response in the frequency range are best use. 

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