Adam Idźkowski

The calibration process and metrological analysis of a transducer used to measure two physical quantities

Abstract This article presents a way of calibration of an unconventional two-current circuit, named 2J+2R, which consists of two current sources and two referential resistors connected to the circuit mass. This bridge was used to measure the beam deflection and the temperature increase simultaneously with the use of a pair of metal strain gauges. This paper contains theoretical and corrected (after calibration) processing characteristics of the measurement circuit. Calibration coefficients of both inputs, responsible for measurement of the measured values in the places where the strain gauges are attached, were calculated. Moreover, the standard combined and expanded uncertainties of both calibration coefficients were calculated and an uncertainty budget was made.

Precautionary Statistical Criteria in the Monitoring Quality of Technological Process

The quality of products depends on a stability of production process. In practice to identify reasons of the process degradation, the Shewhart control chart is typically used. At the construction of control X-charts, it is supposed that the dispersion of sample means in subgroups of data measured in process is caused by the influence of random factors and the limited sample size. In such cases it is an improbable event to obtain the output sample values, which are outside the interval ±3σ. Its appearance indicates the presence of systematic influence and it is the need to adjust the controlled parameters of technological process. Based on practical experience in the ISO 7870-2: 2013 standard it is recommended to pay attention to “… any unusual structure of data points, which may indicate about a manifestation of special (non-random) reasons”. In the numerical example presented in this work the analysis of a structure of points on the control chart showed the presence of non-random values, although if the sample mean values were within interval ±3σ. The indicator of existence of non-randomness was the probability that the minimum number of consecutive selective averages, which got to a certain area did not exceed 0.003. As a result of executed analysis the criteria are established and the algorithm is developed. It helped to identify the dysfunction of technological process at an early stage.

Transforming the Conversion Characteristic of a Measuring System Used for Technical Control

As it is known, the real conversion characteristic of a measuring system is different than the nominal characteristic, e.g. due to lower sensitivity and (or) the presence of nonlinearity. In measurement control, particularly in the areas of the limiting values of tolerance interval, this can increase the effect of random variables, and consequently, this can increase a probability of erroneous decisions. A difference between the real and nominal conversion characteristic of a measuring system is corrected using the calibration procedure. But the real conversion characteristic remains unchanged. Therefore, during calibration it is necessary to transform a conversion characteristic and move it towards the nominal one considering the limiting values. The transformation of characteristic may proceed in several cycles, each one can consist of two phases – multiplicative and additive. In case of the multiplicative transformation, the cycle starts with the multiplicative phase (a change in sensitivity of the conversion characteristic). In this case, the probability of erroneous decisions at both stages, the multiplicative and additive, remains unchanged. In case of the additive transformation in the first (additive) phase of the cycle, there is a parallel displacement of the real conversion characteristic. In this case, in the second (multiplicative) stage, the probability of decision will be β times less than in additive stage cycle. For selecting the type of transformation and the number of cycles it is necessary, first of all, to inspect the relationship between components of errors of conversion measuring system and the length of the tolerance interval which is proportional to β. The relationships, which allow estimating the probability of erroneous decisions (both within a cycle and in the transition to next cycle of transformation) are obtained.

Method to Improve Accuracy of the Chromatography Mass Spectrometry Analysis

The structural-algorithmic methods for improving the accuracy of quantitative chemical analysis are discussed. It is realized with the use of chromatography mass spectrometry measuring system. The idea is presented to exclude the influence of uncertainty at the stage of sample preparation. That allows, for the directly calibrated mass spectrometer, to assess the dispersion and to determine the overall uncertainty of analysis. Considerations are illustrated by numerical example with calibration at five points in a measuring range.

Unconventional Double R/U Converter for Measurement of Two Quantities by a Single Differential Sensor

This paper describes an original four arm single mesh resistance circuit. It has the similar structure as the bridge circuit but is unconventionally supplied by the current source which is switched over between opposite arms. The two output signals of this circuit are sums of two voltages obtained after switching on each bridge diagonal. The processing of this signals allows to find two measured variables which differently influencing arm resistances. The two dimensional (2D) converter of the resistance changes to voltages based on this input circuit is build. It is described in detail and its dynamic properties are examined. The achieved results confirm that this unconventional signal conditioning circuit can be successfully used in continues measurements of two parameters, e.g. two geometrical components of the strain or the strain and temperature by a single differential sensor.