Construction and characterization of inexpensive PRT differential thermometer in temperature interval 20-100 °C

A precise, inexpensive, and mercury-free differential platinum resistance thermometer based on the widely known and used 4 × Pt1000 Wheatstone bridge scheme has been constructed and tested for direct temperature difference measurements. Both a theoretical overview and an experimental study of the 4 × Pt1000 differential thermometer were conducted in laboratory conditions at a temperature interval of 20-100 °C. A comparison between the parameters of the 4 × Pt1000 measurement instrument and those of an alternative less accurate 2 × Pt1000 differential thermometer was made. The results show that the 4 × Pt1000 thermometer performs significantly better in terms of stability and accuracy. A maximal relative error below 0.9% has been achieved with the 4 × Pt1000 measurement device, which equals 0.20 °C in absolute units. Such accuracy is considered higher than that of some reference thermocouples, type S (0.5-1.0 °C). The presented 4 × Pt1000 differential thermometer is a low-cost substitute for thermocouples in various precise narrow-margin measurements of temperature differences in the fields of physics, metrology, chemistry, etc.