The refrigerating machine oil of the invention is characterized by comprising an ester of a polyhydric alcohol and fatty acids with a content of a C10-C13 branched fatty acid of 50% by mole or greater. The fluid flow RTD sensor is incorporated into a Wheatstone bridge circuit which is used to provide increased sensitivity to the outputs of the RTD sensors. An operational status for the identified linking device may be determined by the gateway device. Then the correctness of the filed data is executed either directly in the terminal or the terminal is connected to a datacenter where the checking of the meaningfulness of the filed data is executed.