High-speed Digital Oscilloscope Research Articles

A Fast, Accurate, and Reproducible In-Drive Measurement of Media Thermal Decay

A rapid, in-drive technique for the measurement of the thermal decay rate of the magnetic readback signal amplitude has been developed. The adaptive variable-gain-amplifier (VGA) of the read channel is used to measure the signal amplitude eliminating the need for a high-speed digital oscilloscope. Individual VGA measurements include a noise component significantly larger than the amplitude change due to thermal decay. It was found that by using interleaved sectors of aged reference data, the noise could be dramatically reduced. This report will detail techniques to reduce the noise level of the measurement and techniques to acquire the final thermal decay rate as rapidly as feasible.

Channel addition/removal response in Raman fiber amplifiers: modeling and experimentation

In this article, we investigate, both theoretically and experimentally, transient effects in Raman fiber amplifiers (RFA) caused by channel addition/removal. A comprehensive large-signal numerical model of RFA, which incorporates time variation effects and the downstream and upstream propagation of multiple signals, pumps, and amplified spontaneous emission components, has been used for the theoretical analysis. The effect of pumping scheme, pump power, the length and type of Raman fiber, and number of added and/or dropped channels on the dynamics of surviving channel power fluctuations has been studied. In our experimental setup, signals from two laser diodes (LDs) were transmitted through counterdirectionally pumped RFA consisting of 15.6 km of dispersion compensating fiber (DCF). To simulate channel addition/removal, one signal was square-wave-modulated at 500 Hz. At the output of the RFA, the signal of the continuous-wave LD was selected with an optical bandpass filter, and power fluctuations of the surviving channel were recorded with a high-speed digital oscilloscope. Power fluctuations as high as 0.45 dB with typical saturated amplifier overshoots were observed.

Cross-gain modulation in Raman fiber amplifier: experimentation and modeling

The effects of channel loss on the performance of Raman fiber amplifiers (RFA) are investigated both experimentally and theoretically. Signals from one distributed-feedback (DFB) laser and an external cavity laser (ECL) were transmitted through counterdirectionally pumped RFAs consisting of 15.6 km of dispersion compensating fiber (DCF). The ECL light was square-wave modulated at 500 Hz. At the output of the RFA, the signal of the modulated channel was eliminated with an optical band pass filter, and power fluctuations of the surviving channel were recorded with a high-speed digital oscilloscope. Power fluctuations as high as 0.45 dB with typical saturated amplifier overshoots were observed. The experimental results were confirmed by a large signal numerical analysis.

Characterization of plume fluence for laser ablation of yttria stabilized zirconia in mixed oxygen and argon environments

Pulsed laser deposition (PLD) is a versatile and efficient deposition technique that produces a highly energetic plume, from which films are grown. The plume characteristics are highly dependent on background environment conditions, with low pressure oxygen being the most common choice for the deposition of highly oriented yttria stabilized zirconia (YSZ) films. Emission intensity measurements of the plume excited and ionized species were made using four different narrow band filters in conjunction with a high-speed photomultiplier tube and digital oscilloscope. Experiments were performed with five background gas compositions containing oxygen and argon, at seven different pressures ranging from 0.3 Pa to 26.7 Pa. For Ar/O 2 gas mixtures, there was an optimum background pressure of 1–10 Pa, providing a highest level of plasma ionization and excitation. Plume species were also considerably decelerated through gas collisions at pressures above 1 Pa. For films grown at approximately 1 Pa pressure, the variation of Ar/O 2 background gas compositions had a minor effect on YSZ crystal size and lattice parameters. Film crystallinity was drastically improved, when negative bias was applied to the substrate. This was explained by the presence of Zr ions in the plume, which accelerate with negative bias to provide surface ion bombardment and structure reconstruction.

On-line partial discharge detection in cables

This paper describes an on-line PD (partial discharge) detection technique applicable to power cables. The method can be applied to both wire screen and solid shielded cables. In wire screen shielded cables, PD components with frequencies <100 MHz can be detected at distances over 150 m from the source, PD activity with levels as low as 20 pC can be detected within 100 m. However, in the case of solid shielded cables, PD levels of /spl ges/50 pC can be measured within 60 m in the frequency range <50 MHz. This method also can be utilized to check cable accessories such as splices and terminations. PD pulses with frequencies to /spl sim/300 MHz can be measured near the joints and terminations. The suitability and the sensitivity of the VHF technique were checked against two other alternative PD detecting techniques (pulse phase analyzer and high speed digital oscilloscope) by performing PD measurements in standard air gap and defects induced in EPR-insulated cable under laboratory-controlled conditions. The suitability and sensitivity of the VHF method were as good as the two alternative PD detection techniques.

Ohmic Drop Compensation in Voltammetry: Iterative Correction of the Applied Potential

A new method of ohmic potential drop correction for use with potential step and sweep voltammetric methods is described. The method, iterative correction of the applied potential (ICAP), essentially replaces an electronic positive feedback correction with a digital positive feedback correction. This paper will present one form of the ICAP procedure, in which voltammetric current data acquired by a high-speed digital oscilloscope are used to iteratively generate a compensating potential waveform that is then synthesized by an arbitrary waveform generator. The ICAP method is advantageous for high-speed measurements, since many of the difficulties caused by electronic positive feedback compensation are eliminated.

An algorithm for a real time measurement of nonlinear transition shift by a time domain correlation analysis

An algorithm has been developed for a real time measurement of the nonlinear transition shift in high areal density magnetic recording, by a time domain correlation analysis. By measuring SNR and a correlation coefficient of the time domain readback voltages, r[/spl nu/(t), /spl nu/(t+/spl epsiv//2+(M/sub 1/-1/2)T)], written by a pseudorandom sequence, we can determine the nonlinear transition shift in real time. This new algorithm not only simplifies data processing of the readback waveform, but also includes noise effects on the nonlinear transition shift measurement. This algorithm has been implemented by LeCroy Corporation into their 7200-A high-speed digital oscilloscope. The LeCroy oscilloscope measures the nonlinear transition shift in less than 100 ms utilizing this algorithm. >

A Technique For The Measurement Of Dynamic Mechanical Properties Of Oil Sands

Abstract This paper describes a special technique for the measurement of Young's modulus and maximum compressive strength of Alberta oil sand specimens under confining pressure. A modified split Hopkinson bar facility with a pressure chamber was used to provide the source of dynamic loading. Measured strain data were recorded and processed by a high-speed digital oscilloscope and a microcomputer. Mechanical properties of oil sand specimens at strain rates of up to 2000/s were measured. Results indicated strong sensitivity of these properties to the loading (strain) rates. Introduction As the conventional oil reserves in the world are being depleted at an alarming rate and more exploration of new sources has been initiated in offshore and frontier regions, the vast reserve of oil sand deposits in this country presents a very attractive and viable alternative to make up this shortage. It is estimated that the total in-place volume of heavy hydrocarbons in oil sand deposits is in the order of 3 trillion barrels, which is roughly equal to the total discovered conventional oil reserve in the world. Unfortunately over 80% of the deposits in Alberta are situated at depths of over 150 metres from the ground surface, which makes in-situ processes the only practical production method(1). Oil sand is a densely packed material with a density exceeding 2 Mg/m3. It is usually comprised of four distinct phases: mineral solids, water, bitumen and gases. The extremely high viscosity of the entrapped bitumen makes conventional recovery by pumping virtually impossible. Most in-situ processes thus involve heating the oil sand with pressurized steam or by controlled combustion. Two common problems associated with these processes however, appear to be the poor sweep efficiency and communication between the injection and production wells. Pre-injection in-situ fracture of the oil sand pay zone is considered to be a partially effective method to improve the permeability and hence increase the sweep efficiency for the subsequent steam injection. There are two fracture methods commonly being used in reservoir engineering, namely hydraulic fracturing by pressurized water or steam and dynamic fracturing by explosives. The hydrofracture method is a more commonly used method but was found to be less controllable and often resulting in undesirable fracture patterns. The technology of dynamic in-situ fracture is not as widely used but has been found to be effective in similar applications for hard rock(2). The present authors believe that by introducing proper loading rates and fracture starters at the wellbore, dynamic fracturing can be both effective and controllable. Better understanding of the behaviour of oil sands under dynamic loading conditions is thus necessary. A literature review has failed to reveal any previous measurement of dynamic mechanical properties of oil sand under various loading rates. These properties are a necessary input to the analytical models for the dynamic in-situ fracture design and imulation. This paper will describe the construction of a split Hopkinson bar facility used to measure some key mechanicalroperties of pressurized oil sand specimens. Results have clearly indicated the sensitivity of these properties to the applied loading (or strain rates).