The paper presents results of research on selected physico-chemical parameters of engine oils from farm tractors based on the date of their change assumed by the user. 17 samples of used engine oil from farm tractors of various producers and with a varied exploitation course were analysed. Oils for research were collected during oil change, registering the service life of oil each time. They were obtained from service points that repair farm tractors in the region of Lublin Province. The studies were to verify whether a decision concerning oil change taken by tractor users after specific time of operation of an engine was good. Number of exceedings of the threshold values of parameters of engine oil which are responsible for correct lubrication were the basis for evaluation
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.
The article presents the analysis of metrological properties of a two-current-source supplied circuit. It includes such data as precise and simplified equations for two circuit output voltages in the function of relative resistance increments of sensors. Moreover, graphs showing nonlinearity coefficients of both output voltages for two resistance increments varying widely are presented. Graphs of transfer resistances, depending on relative increments of sensors resistance were also created. The article also contains a description of bridge-based circuit realization with the use of a computer and a data acquisition (DAQ) card. Laboratory measurement of the difference and sum of relative resistance increments of two resistance decade boxes were carried out indirectly with the use of the created measurement system. Measurement errors were calculated and included in the article, as well.