Probe detectors

Neutron probe assembly consisting of probe, detector, scalar (cormting device) and cable (Fig. 2.7)... 

As probes must be manufactured individually for each different tube type, the probe development is an important factor for the economic use of the method. The classical procedure of probe development is a combination of experience and experiment. The new probe design is based on the experience with already manufactured probes. For an evaluation of the new design the probe must be manufactured. If the probe design is complicated, for example due to dual exciter coil arrangement or segmented differential detector coil systems, the costs of the development can be very high. Therefore a method for the pre-calculation of the probe performance is extremely useful. 

The probe receives a signal when either the driver or detector coil passes a flaw or other feature in the tube A signal is produced over the full length of the flaw. It is affected by geometry and permeability changes which cause the instrument zero to wander. 

Combined equipment consisting in flaw detector connected with probes, in the case of frequent-simplified verification (pr EN 12668-3). 

Combined equipment" verification enables to check daily or on site the good working of flaw detector connected to probe. It is based on a set of simplified measurements. 

With the reference block method the distance law of a model reflector is established experimentally prior to each ultrasonic test. The reference reflectors, mostly bore holes, are drilled into the reference block at different distances, e.g. ASME block. Prior to the test, the reference reflectors are scanned, and their maximised echo amplitudes are marked on the screen of the flaw detector. Finally all amplitude points are connected by a curve. This Distance Amplitude Curve (DAC) serves as the registration level and exactly shows the amplitude-over-distance behaviour" of the reference reflector for the probe in use. Also the individual characteristics of the material are automatically considered. However, this curve may only be applied for defect evaluation, in case the reference block and the test object are made of the same material and have undergone the same heat treatment. As with the DGS-Method, the value of any defect evaluation does not consider the shape and orientation of the defect. The reference block method is safe and easy to apply, and the operator need not to have a deep understanding about the theory of distance laws. 

Signal processing in mechanical impedance analysis (MIA) pulse flaw detectors by means of cross correlation function (CCF) is described. Calculations are carried out for two types of signals, used in operation with single contact and twin contact probes. It is shown that thi.s processing can increase the sensitivity and signal to noise ratio. 

A connnon teclmique used to enliance the signal-to-noise ratio for weak modes is to inject a local oscillator field polarized parallel to the RIKE field at the detector. This local oscillator field is derived from the probe laser and will add coherently to the RIKE field [96]. The relative phase of the local oscillator and the RIKE field is an important parameter in describing the optical heterodyne detected (OHD)-RIKES spectrum. If the local oscillator at the detector is in phase with the probe wave, the heterodyne mtensity is proportional to... 

Recently, the state-selective detection of reaction products tluough infrared absorption on vibrational transitions has been achieved and applied to the study of HF products from the F + H2 reaction by Nesbitt and co-workers (Chapman et al [7]). The relatively low sensitivity for direct absorption has been circumvented by the use of a multi-pass absorption arrangement with a narrow-band tunable infrared laser and dual beam differential detection of the incident and transmission beams on matched detectors. A particular advantage of probing the products tluough absorption is that the absolute concentration of the product molecules in a given vibration-rotation state can be detenuined. 

The detector D monitors the absorption of the probe beam as a function of the delay between the pulses given by xHc, where c is the speed of light and v is the difference between the optical path travelled by the probe and by the pump pulse. Adapted from [110],... 

Figure C3.1.1. The basic elements of a time-resolved spectral measurement. A pump source perturbs tlie sample and initiates changes to be studied. Lasers, capacitive-discharge Joule heaters and rapid reagent mixers are some examples of pump sources. The probe and detector monitor spectroscopic changes associated with absorjDtion, fluorescence, Raman scattering or any otlier spectral approach tliat can distinguish the initial, intennediate and final...

Optical detectors can routinely measure only intensities (proportional to the square of the electric field), whether of optical pulses, CW beams or quasi-CW beams the latter signifying conditions where the pulse train has an interval between pulses which is much shorter than the response time of the detector. It is clear that experiments must be designed in such a way that pump-induced changes in the sample cause changes in the intensify of the probe pulse or beam. It may happen, for example, that the absorjDtion coefficient of the sample is affected by the pump pulse. In other words, due to the pump pulse the transparency of the sample becomes larger or smaller compared with the unperturbed sample. Let us stress that even when the optical density (OD) of the sample is large, let us say OD 1, and the pump-induced change is relatively weak, say 10 , it is the latter that carries positive infonnation. 

Direct photography of drops in done with the use of fiber optic probes using either direct or reflected light. StiU or video pictures can be obtained for detailed analysis. The light transmittance method uses three components a light source to provide a uniform collimated beam, a sensitive light detector, and an electronic circuit to measure the amplified output of the detector. The ratio of incident light intensity to transmitted intensity is related to interfacial area per unit volume. 

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