Thermal imaging observations of the surface of a gauge block

Abstract

This paper proposes a method for determining the time at which the temperature of surface of a gauge block will be established. The relationship between the temperature of a gauge block, its length and the value of uncertainty of measurement when calibrating using this block was explained. Attention was paid to problems resulting from the applied measurement method. Particular attention was paid to thermal imaging observations of the lateral surface of a gauge block PrefaceThe gauge blocks are rectangular length standards. Most often they are made of tool steel. The dimensions of a gauge block are subject to change as a result of the change in the value of its temperature. A change in the temperature of a gauge block may be caused, among others, by a change in ambient temperature or by a touch of hand. The actual length of the gauge block can be expressed by equation (1).where l s -the length of gauge block at the reference temperature t o = 20 °C given in the calibration certificate, δl D -change in the length of gauge block since the last calibration due to drift, δl -measured difference in the length of both gauge blocks, δl Ccorrection for non-linearity and inaccuracy of the comparator setting, L -nominal length of gauge block, α '-mean value of the thermal expansion coefficient of both gauge blocks, δl t -temperature difference of gauge blocks, δ α -difference of the thermal expansion coefficients of both gauge blocks, Δt'deviation of the mean temperature of gauge block and a plate calibrated from the ambient temperature, δl v -correction for the non-centricity of contact with the measuring surfaces of gauge block.While analysing the above equation one can notice the effect of temperature of gauge blocks on the determined difference in length between the gauge block and calibrated plate and the uncertainty of the difference measured. For this reason, in order to measure the difference between the length of gauge block and the calibrated plate, the temperature of calibrated plate should be equalized with the temperature of gauge block. The aim of the research conducted was to determine the time in which the temperature of lateral surface of gauge block is established.2 Methodology of conducted worksIn the works conducted, essential is the selection of method by which the temperature of lateral surface of the gauge block was recorded. In order to obtain a reliable distribution of temperature on the lateral surface of gauge blocked, a large number of measuring sensors should be placed. This would increase the thermal capacity of the entire system (calibrated plate and measuring sensors). Consequently, the time in which the temperature of plate with sensors placed would have reached the ambient temperature would differ from the time in which the plate without the sensors would have reached the ambient temperature. Impossibility to obtain appropriate thermal connections between the surface of gauge block and the surface of sensor should also be mentioned. In order to protect the plate from damage caused by the ef...