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Voltage standards are widely used to transfer volts from Josephson voltage standards (JVSs) at national metrology institutes (NMIs) into calibration labs to maintain the volts and to transfer them to test equipment at production lines. Therefore, commercial voltage standards based on Zener diodes are used. Analog Devices Inc. (San Jose, CA, USA), namely, Eric Modica, introduced the ADR1000KHZ, a successor to the legendary LTZ1000, at the Metrology Meeting 2021. The first production samples were already available prior to this event. In this article, this new temperature-stabilized Zener diode is compared to several others as per datasheet specifications. Motivated by the superior parameters, a 10 V transfer standard prototype for laboratory use with commercial off-the-shelf components such as resistor networks and chopper amplifiers was built. How much effort it takes to reach the given parameters was investigated. This paper describes how the reference was set up to operate it at its zero-temperature coefficient (z.t.c.) temperature and to lower the requirements for the oven stability. Furthermore, it is shown how the overall temperature coefficient (t.c.) of the circuit was reduced. For the buffered Zener voltage, a t.c. of almost zero, and with amplification to 10 V, a t.c. of <0.01 µV/V/K was achieved in a temperature span of 15 to 31 °C. For the buffered Zener voltage, a noise of ~584 nVp-p and for the 10 V output, ~805 nVp-p were obtained. Finally, 850 days of drift data were taken by comparing the transfer standard prototype to two Fluke 7000 voltage standards according to the method described in NBS Technical Note 430. The drift specification was, however, not met. [ABSTRACT FROM AUTHOR]

We have been investigating the long-term drift of pressure gauges under constant pressure application with the aim to improve the precision of pressure monitoring at seafloor. This paper focuses on the effect of surrounding temperature on the long-term drift of quartz Bourdon-type pressure gauges. The pressure of 100 MPa was continuously applied to the test gauge for several months at 3 °C and 23 °C. The calibration results at 100 MPa and those at atmospheric pressure were traced. The long-term drift at 3 °C was much smaller than that at 23 °C. In addition, the variations in the calibration results at 100 MPa and 0 MPa were different at 3 °C, whereas the two variations were identical at 23 °C. The effect of temperature on the drift characteristics should be considered for the appropriate selection of gauges and procedure of the actual pressure monitoring at seafloor.

Borehole tiltmeters are widely used to continuously record small surface deformation of reservoirs and volcanoes. Because these instruments display unknown long-term drift, only short-term tilt signal can be used for monitoring purpose. We propose a method to invert long-term time series of tilt data induced by strain variations at depth. The assumption that tiltmeter drift is linear over time is on its own insufficient to remove the drift and uniquely determine the deformation source parameters. To overcome this problem, we first invert the data with no constrain on the drift to obtain one particular solution among all admissible. Then, using the linearity of the forward model, we use the statistical properties of the drift distributions to restore the uniqueness of the solution. We illustrate our approach with four synthetic cases simulating volume changes of a reservoir. We demonstrate the efficiency of our method and show that the accuracy of estimated volume variation dramatically improves if low drift tiltmeters are used. [ABSTRACT FROM AUTHOR]

• The long-term drift of pressure gauges under constant high pressure was evaluated. • Calibration values under 100 MPa application have been traced for 800 days. • The drift trend under pressure was different from that under atmospheric pressure. • Preliminary pressure application can reduce the initial drift during actual use. • Most part of the drift under pressure can be corrected by zero offset on site. We have evaluated a long-term drift of hydraulic pressure gauges which are kept under constant pressure application. Three pressure gauges were pressurized and kept at 100 MPa, and the variations in calibration results at 100 MPa have been traced for 800 days. The calibration results significantly varied immediately after the pressure application, and the variation rate became small and almost constant as the pressure was continuously applied. The observed drift trend was different from the drift which is observed when the gauges are always kept at atmospheric pressure. In addition, during the pressure application, the pressure was intermittently released to atmospheric pressure for a short time, and outputs at atmospheric pressure were obtained. The calibration results at 100 MPa and atmospheric pressure showed a similar drift trend, showing that most part of the drift under pressure can be corrected by zero offset. Several methods are proposed to appropriately evaluate and correct the long-term drift of pressure gauges during use under constant pressure application. [ABSTRACT FROM AUTHOR]

Surface deformation measured by geodetic data is the sum of single-strain sources deforming at depth. A combination of volume changes from several analytical models (e.g. a point source or dislocation along a plane) can be used to model the different sources. However, solving for the best fit of volume variations, dislocations, position and orientation parameters of all sources is a nonlinear problem, and its solution is generally non-unique. This problem can be converted into a linear one by assimilating the sum of sources to a simplified model formed by three orthogonal planes of dislocations at fixed position and orientation. This strain source model is equivalent to having all neighbouring deformation sources contained in a small size volume. The determination of the strain tensor components can be performed by inverting geodetic data. Because of their high resolution, tiltmeters are well adapted to survey shallow deformation of volcanoes and geological reservoirs. However, they are known to display unknown long-term drift. We propose an approach to jointly estimate the temporal evolution of the strain source and time-dependent instrumental parameters. We verify the approach using synthetic data, giving confidence intervals for each component of the strain tensor. Finally, we link geological information to the internal deformation by interpreting the strain tensor as principal directions of deformation. This approach seems promising for the identification of fracture onset and fault reactivation in geothermal, hydrocarbon exploitations or volcanic systems. [ABSTRACT FROM AUTHOR]

An active beam-pointing stabilization system has been developed for a high-power KrF laser system to eliminate the long-term drift of the directional change of the beam in order to have a stable focusing to a high intensity. The control of the beam direction was achieved by a motor-driven mirror activated by an electric signal obtained by monitoring the position of the focus of the output beam. Instead of large sized UV-sensitive position sensitive detectors a simple arrangement with scatter plates and photodiodes are used to measure the directionality of the beam. After the beam stabilization the long-term residual deviation of the laser shots is ~14 μrad, which is comparable to the shot-to-shot variation of the beam (~12 μrad). This deviation is small enough to keep the focal spot size in a micrometer range when tightly focusing the beam using off-axis parabolic mirrors.

Drift is an important phenomenon of capacitive humidity sensor, the most vital device in the commercial dew point meter. Due to drift in the output, most of the meters for critical applications require costly and time-consuming recalibration. Modeling of drift phenomenon for RH humidity sensors was reported in various literature. But to the best of our knowledge, there is no work reported so far about the drift of the sensors utilized for trace level moisture detection. This paper presents the mathematical model, the electrical equivalent circuits, and long-term drift analysis of the aged capacitive sensors for trace moisture sensing. The sensors were fabricated using porous alumina oxide thin film for detecting moisture in the range of 3 to 100 ppm. To study the long-term drift, experiments were performed under different operating conditions over a period of nearly one year. The response behaviors of the sensors were simulated with the help of the model. Comparing the model response with the experimental results, the proposed model can be used for drift analysis for an aged sensor, determination of hydration level and moisture condensation inside the pores. Experimental results showed that when a sensor was kept in drying agent, a maximum average drift of only 1.50% was observed but when a similar sensor was kept in open high humidity atmosphere, the maximum long-term drift was found to be ~11.20%. [ABSTRACT FROM AUTHOR]

We report laser frequency stabilization with modulation transfer spectroscopy (MTS) on Rb atoms. With both PZT (piezo-electric transducer) slow-loop feedback and current fastloop feedback to the laser head, we get a linewidth narrowing less than 5 kHz simultaneously. Laser injection to a laser diode and frequency beating with another polarization spectroscopy based stabilization setup are also employed to check the narrow linewidth property. With the help of the technique, a linewidth around kHz-level laser is obtained and pave the way for the locking of the lattice laser of ytterbium clock with transfer cavity technique. The setup can be used as a frequency reference for precise frequency control of atomic clock system. [ABSTRACT FROM AUTHOR]

Chemical analysis of old triple-point-of-water (TPW) cells has shown that the dominant impurities in the water are the principal constituents of borosilicate glass, which suggests the long-term downward drift observed in the realized triple-point temperature of TPW cells is caused by gradual dissolution of the glass containers. Because some of the glass constituents contribute to the electrical conductivity of the water, measurement of the conductivity provides a possible means for monitoring the long-term drift of TPW cells. This paper investigates the utility of a conductivity measurement, based on the measurement of a capacitor using the TPW cell as a dielectric, as a non-destructive means for monitoring the long-term stability of cells. The measurement exploits the cylindrical geometry of the cell and uses a two-terminal-pair coaxial electrical definition of capacitance. The results include estimates of the sensitivity of the method and examples of the long-term behavior of TPW cells, some as old as 38 years and monitored for periods of up to 10 years. It is found that the conductivity measurements correlate well with the cell age, with the drift rates increasing with time, as expected from the chemical model of glass dissolution. Measurements of temperature differences between cells show the technique can detect changes as small as $$10~\upmu \hbox {K}$$ , and therefore the method is a useful means of monitoring TPW cells. [ABSTRACT FROM AUTHOR]

The MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands, covering a wavelength range from 0.4 to 14.4 μm. Terra MODIS band 27 (6.72 μm), a water vapor band, was found to have electronic crosstalk from other bands located on the same focal plane assembly, which causes surface feature contamination and pronounced detector level striping in the images. In a previous study, an algorithm using a linear approximation derived from on-orbit lunar observations was developed to correct the crosstalk effect. Results demonstrated that the correction substantially reduces the striping and removes the contaminated surface features. However, it was also demonstrated that the crosstalk effect might bring about a long-term increase in the brightness temperatures (BTs) in Terra band 27. In this paper, it is shown that there is a long-term drift (or decrease), which is strongly detector dependent, in the BT for the band induced by the crosstalk effect. It is also shown that the crosstalk correction with the linear algorithm substantially removes the detector-dependent long-term drift and greatly improves the radiometric accuracy of the band. The comparison between the BT of Terra band 27 in the most recent MODIS Level 1B (L1B) collection [Collection 6 (C6)] and those from the Infrared Atmospheric Sounding Interferometer using simultaneous-nadir-overpass observations shows that the detector-averaged long-term drift in the BT in Terra band 27 varies from approximately 1 K to 3 K. The detector difference can be as large as 9 K for a few detectors during the last five years in the northern and southern polar areas. With crosstalk correction applied, the long-term drift is reduced to be less than 0.5 K, and the detector difference is within 1 K. The crosstalk effect-induced detector-dependent long-term drift in Terra band 27 and the capability of the crosstalk correction algorithm to remove the drift are also assessed at three well-characterized sites with different radiance levels, namely, Dome Concordia (Dome C), Libya 1, and the Pacific Ocean at various radiometric levels. The long-term drift and the strong detector dependence of the drift are clearly observed at the three sites with the BT in the Terra band 27 C6 L1B products. The band-averaged BT drifts are about 0.8 K, 5 K, and 5.5 K, and the detector differences can be as large as 4 K, 12 K, and 15 K, respectively, for the three sites. With the crosstalk correction applied, the long-term drifts in the BT over the three sites are substantially removed, and the observed detector differences of Terra band 27 at the three sites are also significantly reduced. The crosstalk correction greatly improves the radiometric accuracy of the band as well as the image quality. [ABSTRACT FROM PUBLISHER]

Abstract: Aging of porous silicon (PS) material is one of the important constraints for its large-scale commercial use as an accurate and reliable humidity sensor. It causes gradual drift of the sensor output with the passage of time. Present paper reports the systematic studies on the aging of the porous silicon humidity sensor with an objective to develop a signal-processing unit to compensate its long-term drift. Drift of the porous silicon sensor is first determined experimentally by periodic recalibration of the sensor with respect to a standard sensor. An ANN-based model is then developed, which can compensate drift due to its aging. Compensating ANN model is then hardware implemented using a simple electronics circuit. Experimental results using the circuit show that drift of approximately 13.5% has been compensated effectively. [Copyright &y& Elsevier]

Abstract: An approach to enhance accuracy of the output signal obtained from ISFET interface electronics due to the body effect is proposed. Based on an MOS drawing the same drain current as the ISFET, the scheme allows reduction of influence of body effect. The presented readout interface improves the accuracy of pH measurements, while maintaining operation at constant drain-source voltage and current condition. Using only one ISFET with a differential output configuration, we obtained temperature-dependency and long-term drift as well as common noise compensation. The proposed technique is simple and has a universal use for different ISFETs. In addition, a voltage-controlled dc offset error compensation circuit modulates the extracted signal to the desired dc level for the A/D converter for each sensor. Simulation and experimental results show a great effect on monolithic ISFET integration in CMOS technology. [Copyright &y& Elsevier]

Ion sensitive field effect transistor (ISFET) and membrane field effect transistor (MEMFET) have some drawbacks related to: long-term drift, hysteresis and thermal drift. These factors limit the accuracy of ISFET/MEMFET based measurements systems, specially for continuous or long period measurements. Due to its accuracy, repeatability and easy-to-use features, electronic instrumentation systems are the best tools to design ISFET/MEMFET based measurement systems. A well-designed hardware and a qualified virtual instrumentation software are the key factors to overcome and compensate hysteresis, thermal and long-term drifts ISFET/MEMFET limitations. The paper is dedicated to show an instrumentation system designed to compensate long-term drift on ISFET/MEMFETs. First, this limitation is experimentally shown. As a consequence of it, an electronic hardware is designed to supply correct sensor voltage and current bias levels. On the other hand, an acquisition and control algorithm is implemented. The software acts over the hardware selecting appropriate voltage bias levels compensating sensor drifts. Experimental results demonstrate the effectiveness and feasibility of the instrumentation system proposed. [Copyright &y& Elsevier]

Summary Background. Intracranial pressure (ICP) monitoring is dependent on the precise measurement of absolute pressures and low drifts of the different transducers in use. Our investigations have shown that probes sometimes appear to reveal positive and negative drifts consecutively. There is no regard for any of these important pressure changes by the mere result of the traditional drift. Therefore, we have developed a more precise way of assessing the behavior of the ICP drift. Method. A special laboratory set up for the simulation of constant pressures, at definite temperatures, was designed. We examined the Camino®-110-4B, Gaeltec® ICT/B, HanniSet® and Spiegelberg® transducers. Drift index is a new term that has been developed by our group to provide a better description of the actual pressure changes over long-term measurement. The drift index consists of three parameters: the percentage of measurements which show a pressure change during the 10 days of measurement; the maximum absolute pressure deviation that occurred during a ten day measurement; and the mean absolute pressure deviation during a 10 day measurement. Findings. The median proportion of pressure changes during ten days were: Camino: 1.59%; Gaeltec: 0.71%; HanniSet: 0.08%; Spiegelberg: 4.00%; The median maximum absolute pressure changes were 6; 9.5; 1; and 11 mmHg for the four types and the median mean absolute pressure changes were 2.9; 5.1; 0; and 2.4 mmHg, respectively. The median 10 day classical drift in each type of transducer was 4; 9; 0; and 2 mmHg, respectively. Interpretation. We recommend the use of the drift index to be used by manufacturers. This is an additional vital parameter in order to improve ICP measurement accuracy and the proficiency of ICP monitoring. [ABSTRACT FROM AUTHOR]

In a backward Er-doped superfluorescent fiber source (SFS), we report the observation of large mean wavelength variations (>100 ppm) induced by external perturbations of the fiber birefringence. These previously unreported variations, which need to be reduced to the ppm level for high-accuracy fiber-optic gyroscope applications, are shown to originate first from polarization-dependent gain induced by the polarized pump source, and second from a slight polarization dependence of the SFS wavelength division multiplexing (WDM) coupler and fiber isolator. We demonstrate that these effects can be substantially reduced by incorporating two Lyot fiber depolarizers in the source. The new depolarized SFS exhibits short-term mean wavelength stability of ±2.5 ppm and a long-term drift of ±3 ppm. The latter is probably due mostly to slow variations in the Er-doped fiber temperature, which can be eliminated with a simple temperature control to ~0.1°C [ABSTRACT FROM PUBLISHER]

Background: Intraocular pressure (IOP) is well known to be associated with blood pressure and other cardiovascular risk factors. The influence of systemic cardiovascular, in particular antihypertensive, medication on IOP is still controversial. This study analyses the association between the use of cardiovascular medications and IOP in a large European cohort., Methods: The Gutenberg Health Study is a population-based, prospective,observational cohort study in mid-western Germany. IOP was measured using a non-contact tonometer. The medication classes examined were peripheral vasodilators, diuretics, β-blockers (overall, selective and non-selective), calcium channel blockers, renin-angiotensin blockers (overall, ACE inhibitors and angiotensin-receptor blockers), nitrates, other antihypertensive medications, aspirin and statins. Subjects with missing IOP values, topical IOP-lowering medication or previous ocular surgery were excluded. In total, 13 527 subjects were enrolled in this study. Association analyses between medication use and IOP were performed using multivariable linear regression (p<0.0038)., Results: Neither selective nor non-selective systemic β-blocker intake was associated with statistically significant lower IOP (-0.12 mm Hg, p=0.054 and -0.70 mm Hg, p=0.037, respectively). IOP was not associated with the use of ACE inhibitors after adjustment for body mass index, systolic blood pressure and central corneal thickness (0.11 mm Hg; p=0.07)., Conclusions: None of the cardiovascular medications, in particular systemic β-blocking agents, showed an association with IOP in non-glaucoma subjects. The long-term drift phenomenon of topical and systemic β-blocker might explain this result. Our results suggest that systemic β-blockers have a negligible effect on IOP reduction., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)