Measuring air velocity with a thermopile

A NEW-TYPE anemometer has been developed which allows velocities as low as five feet per minute to be determined as accurately as the higher velocities. It operates by placing a heated thermopile in an air stream whose velocity is to be measured. The flow of air past the thermopile tends to bring the thermopile wire, consisting of a succession of thermojunctions, to the same temperature throughout. The thermal differences between these junctions induce a thermal direct voltage which is proportional to the temperature differences. Thus, flow of air past the thermopile tends to reduce this temperature difference and therefore, to reduce the direct voltage generated by the thermopile.