Described here are the configurations and procedures used to provide traceability to electrical standards for an aerosol electrometer calibration in the range ± 20 fA to ± 40 fA. The technique used here simulated the condition of a current induced when charged particles would flow into the aerosol electrometer’s Faraday-cup by replacing the charged particle flow with known source currents. The technique used here was to source known currents over a wider range of ± 1 pA, in addition to the ± 20 fA to ± 40 fA, and subtract the offset (i.e. zero) current measured when charged particles are not flowing into the aerosol electrometer. Linear regression was used to scale from the pA to fA range by determining the slope of the sourced vs. measured currents over both ranges and using the residuals to verify the linearity. Two independent methods, both traceable to electrical standards, were used to source known currents from ± 1 pA to ± 20 fA: a source-meter and a voltage-resistor source using high resistance standards of 100 GΩ or 1 TΩ.

This paper presents a method to estimate the impedance response of a vibrating wire viscosity sensor. The method is based on the application of a multi-harmonic signal at the terminals of the sensor. The signal is composed by the harmonics that correspond to the frequencies at which one wants to obtain the impedance of the sensor. The impedance is determined using least-squares (LS) multi-harmonic fitting algorithms to estimate the amplitudes and phases of the harmonics of the impedance current and voltage. The measurement and estimation procedure is performed by a dedicated developed measurement system. It includes a digital signal processor (DSP) to perform all the calculations, programmable gain instrumentation amplifiers (PGIA) and analog to digital converters (ADC) to amplify and acquire the signals across the sensor and a reference impedance used to limit and sample the current flowing through the wire of the sensor. The system is connected via USB to a personal computer (PC) where the measurement results can be stored, interpreted and further processed.

This paper presents a new, simple and efficient dual-slope Capacitance-to-Digital Converter (CDC) that gives digital values of capacitances in a π-model of a capacitive proximity sensor. This CDC is suitable for a capacitive proximity sensor with two electrodes. When a human approaches the electrodes, it forms three capacitances, i.e., between human body and first electrode, between body and second electrode and between body and ground. It can be represented in a T-model or in an equivalent π-model. Conventional signal conditioning methods can provide only a single output from this network. It will be very useful, in a proximity sensing point of view, if the signal conditioning circuit can capture changes in those three individual capacitances and provide corresponding outputs. Further it will also be useful, to store and process easily, if these outputs are obtained in digital form, directly. A novel dual-slope CDC that measures all the three values of the capacitances in a π-model and provides those three digital outputs has been developed and details are presented in this paper. Measuring all the three capacitance is advantageous because it can detect proximity as well as provides location of body in relation to sensor electrodes. A prototype CDC has been developed and tested. Results are promising.

In this work we analyse the applicability of low-frequency (LF) noise measurement in order to study the defectiveness in the gate oxide of power MOSFETs. To this purpose we implement a low-noise experimental set-up, which is able to measure the drain current flicker (“1/f”) noise of the device under test (DUT). First, we show how these measurements can be used to empirically detect the physical model and related compact expressions, which best describe the source of fluctuations in this type of devices. Then, accordingly to the selected physical model, the defect density in the gate oxide is extracted. In order to validate the proposed methodology, experimental data are reported and discussed in the case of trench power MOSFETs. The measured noise spectra confirm the suitability of the laboratory set-up for this type of analysis and, by means of an empirical fitting of the data, the defect density is estimated, in accordance with the typical values expected for the technology considered.

A large variety of time synchronization protocols for wireless sensor networks has been suggested. Yet, setting up a sensor network for synchronized data acquisition based on those algorithms is not a trivial task.
This paper outlines two different approaches to time synchronous sampling in wireless sensor networks, discusses their advantages and disadvantages and gives recommendations on when to chose which approach.