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1 Metrology and Measurement Systems
1 Polish Journal of Chemistry
1 Prace Naukowe Instytutu Maszyn, Napędów i Pomiarów Elektrycznych Politechniki Wrocławskiej. Studia i Materiały
1 Scientific Papers of The Institute of Electrical Machines, Drives and Measurements of the Wrocław University of Science and Technology Series: Studies and Research

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Voltage coefficient of high-ohmic mox type resistors

Kłos Z., Krysiak J.

Prace Naukowe Instytutu Maszyn, Napędów i Pomiarów Elektrycznych Politechniki Wrocławskiej. Studia i Materiały

2009

Vol. 63, nr 29

487-500

MOX-type high-ohmic precise resistors are used both in highest resistance standards and in structures of pico-ammeters and mega-ohmmeters with highest measuring ranges. The parameters of applied resistors decides about instrument's accuracy class, available measuring ranges and also have influence on measurement results stabilization time. High-ohmic resistors, especially those with highest resistance values, show considerable voltage unstablility. Larger when forcing voltages are lower. One of the most important parameters of precise high-ohmic resistors besides quality of work tolerance, temperature coefficient (TCR) and noise tension is VCR - the Voltage Coefficient of Resistance. This coefficient is given by the producers usually for voltages higher than 10 V [1]. Therefore when there occurs a need of high-ohmic resistor use for different working voltage an resistance vs. voltagemeasurement R=f(U) has to be made. The article shows obtained up to now results of MOX high-ohmic resistors voltage coefficients examinations in wide range (1-1000) V. The method of obtaining VCR presented in this article can be applied also for determination of MOX high-ohmic resistors parameters in the lowest working voltages.

Synthesis and Selected Transformations of Optically Active Cyclopentenyl Sulfoxides: New Approach o Optically Active Cyclopentenones

Midura W., Krysiak J., Wieczorek M., Filipczak A.

Polish Journal of Chemistry

2007

Vol. 81, nr 2

211-223

The tandem Michael addition – Horner olefination reaction of (S)- alfa-(diethoxyphosphoryl) vinyl p-tolyl sulfoxide was applied for the synthesis of optically active cyclopentenyl sulfoxides, whichwere converted into the corresponding cyclopentenones by Pummerer reaction with trifluroacetic anhydride. The sequence comprising the tandem Michael – Horner reaction, separation of diastereomers and Pummerer reaction afforded enantiomerically pure substituted cyclopentenones.

Factors limiting extremely sensitive measuring ranges of contemporary picoammeter

Kłos Z., Krysiak J.

Metrology and Measurement Systems

2007

Vol. 14, nr 4

603-633

In the paper the principle of operation of contemporary picoammeters with analog conversion of current into voltage has been presented. The influence of factors disturbing the i/u conversion in a passive as well as in an active converter has been analyzed. It has been shown that a picoammeter with the most sensitive ranges should base on active i/u conversion. In detailed considerations maximal errors coming from internal sources (i.e. input bias current, offset, noise currents and noise voltages of ampli.er and thermal noise of a high-ohm scaling resistor) as well as external disturbances (leakage currents of printed board and insulators and disturbances in leading cables) have been discussed and evaluated. From this analysis it can be concluded that on the extremely sensitive ranges the most leading impact on the accuracy of the current measurement have the following factors: the input bias current of the electrometric amplifier, accuracy of the scaling resistor and its thermal noise. These factors limit the extremely sensitive ranges of picoammeter to the level of 10÷20 pA with an accuracy of 1.2%. The presented considerations can be helpful for designers as well as for users of extremely sensitive picoammeters because they permit to avoid some errors caused by improper configuration of the measuring circuit and to distinguish disturbances coming from different sources.