Transit time

The sonic tool measures the time taken for a sound wave to pass through the formation. Sound waves travel in high density (i.e. low porosity) formation faster than in low density (high porosity) formation. The porosity can be determined by measuring the transit time for the sound wave to travel between a transmitter and receiver, provided the rock matrix and fluid are known. 

Shear Horizontal (SH) waves generated by Electromagnetic Acoustic Transducer (EMAT) have been used for sizing fatigue cracks and machined notches in steels by Time-of-Flight Diffraction (TOED) method. The used EMATs have been Phased Array-Probes and have been operated by State-of-the-art PC based phased array systems. Test and system parameters have been optimised to maximise defect detection and signal processing methods have been applied to improve accuracy in the transit time measurements. 

In situ control and calibration of flare and other gas metering systems is performed by gaseous tracers using the transit time method without affecting the normal production. Details about methodology are given in / /. 

A separator is fed with a condensate/gas mixture. The condensate leaves the bottom of the separator, passes a flowmeter and is followed by a choke valve, after which the condensate is boiling. The flow can not be measured using the transit time method, due to the combination of short piping, the absence of a suitable injection point and the flow properties of the condensate, which is non-newtonian due to a high contents of wax particles The condensate can not be representatively sampled, as it boils upon depressuratioh... 

Many experimental techniques now provide details of dynamical events on short timescales. Time-dependent theory, such as END, offer the capabilities to obtain information about the details of the transition from initial-to-final states in reactive processes. The assumptions of time-dependent perturbation theory coupled with Fermi s Golden Rule, namely, that there are well-defined (unperturbed) initial and final states and that these are occupied for times, which are long compared to the transition time, no longer necessarily apply. Therefore, truly dynamical methods become very appealing and the results from such theoretical methods can be shown as movies or time lapse photography. 

The technique just described requires the porous medium to be sealed in a cell, so It cannot be used with pellets of irregular shape or granular material. For such materials an alternative technique Introduced by Eberly [64] is attractive. In Eberly s method the porous pellets or granules are packed into a tube through which the carrier gas flows steadily. A sharp pulse of tracer gas is then injected at the entry to the tube, and Its transit time through the tube and spreading at the exit are observed. A "chromatographic" system of this sort is very attractive to the experimenter,... 

The average linear velocity u of the mobile phase in terms of the column length L and the average linear velocity of eluent (which is measured by the transit time of a nonretained solute) is... 

Ultrasonic Flow Meters. Ultrasonic flow meters can be divided into three broad groups passive or turbulent noise flow meters, Doppler or frequency-shift flow meters, and transit time flow meters. 

The flow velocity is thus proportional to the difference in transit time between the upstream and downstream directions and to the square of the speed of sound in the fluid. Because sonic velocity varies with fluid properties, some designs derive compensation signals from the sum of the transit times which can also be shown to be proportional to C. 

A variation on the transit time method is the frequency-difference or sing-around method. In this technique, pulses are transmitted between two pairs of diagonally mounted transducers. The receipt of a pulse is used to trigger the next pulse. Alternatively this can be done using one pair of transducers where each acts alternately as transmitter and receiver. The frequency of pulses in each loop is given by... 

In practice is a small number and the sing-around frequencies are scaled up for display. In one example, for a pipe 1 m in diameter and water flowing at 2 m/s, the frequency difference is 1.4 Hz (10). Frequency difference transit time meters provide greater resolution than normal transit time ultrasonic meters. The greatest appHcation is in sizes from 100 mm to 1 m diameter. 

As of this writing, it has not been possible to use the seismic data which defines the volume of the reservoir to also determine the joint stmcture. Extended flow testing is the most direct measure of the efficiency and sustainabiUty of energy recovery from the reservoir. The use of chemical tracers in the circulating fluid can also provide valuable supporting data with regard to the multiplicity of flow paths and the transit time of fluid within the reservoir (37). 

Sample Integrity. In order to be able to rely on the results of measurements, it is necessary to be sure that the sample as analy2ed is the same as it was when collected, and that it is properly identified in the field, in the laboratory, and in the report. Transit times and temperatures should be within the limits allowed for the type of sample and analysis. A series of documents which estabhsh a chain of custody should exist so that it is possible to be sure that the right result goes with the right sample. 

In most ultrasonic tests, the significant echo signal often is the one having the maximum ampHtude. This ampHtude is affected by the selection of the beam angle, and the position and direction from which it interrogates the flaw. The depth of flaws is often deterrnined to considerable precision by the transit time of the pulses within the test material. The relative reflecting power of discontinuities is deterrnined by comparison of the test signal with echoes from artificial discontinuities such as flat-bottomed holes, side-drilled holes, and notches in reference test blocks. This technique provides some standardized tests for sound beam attenuation and ultrasonic equipment beam spread. 

The transient current, derivable from equation 1, is given in equations 2 and 3 where T is the transit time and I is the absorbed photon flux. The parameter a can be further derived as equation 4 (4), where Tis the absolute temperature and is the distribution width (in units of kT) of a series of exponential traps. In this context, the carrier mobdity is governed by trapping and detrapping processes at these sites. 

When Uq3 > Up the MOSEET conducts. The conduction current is deterrnined by 1 where Q is the amount of charge in the inversion layer and t is the transit time for electrons to travel from source to drain. Q = C LW (U g — Up) where C = is the gate oxide capacitance per unit area... 

Transition. This is a temporaiy state that is only possible after the valve has been commanded to change state. The limit switch inputs are not consistent with the commanded state, but the transition time has not expired. 

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