Calculation of the components of the temperature measurement error by a resistance thermocouple of an installed unbalanced bridge

The article has devoted to solving an urgent problem related to the determination and calculation of the components of the temperature measurement error. A grain drying machine had selected as the object of research, in which the temperature of the grain at the exit from the machine is measured with the help of a Cu50 resistance thermocouple installed in an unbalanced bridge. It had found that the scale of the measuring device, calibrated in degrees Celsius, will have a nonlinearity error, which increases towards the end of the measurement range. For the Cu50 resistance thermocouple installed in the grain drying machine, when measuring the temperature in the range of 0 … 100 °C in absolute terms, the nonlinearity error was 0.3 mA, in relative terms - 4.4 %, which is quite large. The measurement error has calculated with a tolerance for the nominal resistance of the thermistor ± 0.1 Ohm, which in the given form was 0.5%. The resulting value indicates that this component will have an insignificant effect on the total measurement error. The measurement error due to the supply voltage drop by 0.2 V in relative form was 4.2 %. Thus, the voltage drops when using an unbalanced bridge will have a significant effect on the measurement result.