A silicon micromachined flow sensor using thermopiles for heat transfer measurements

A silicon micromachined flow sensor composed of a platinum heater and four thermopiles centered at the heater is described. Two of the four thermopiles, placed up- and down-stream of the flow, measure the heat carried by the fluid, while the other two, arranged perpendicular to the flow direction, monitor the heat transferred from the heater to the fluid. This architecture allows the normalization of the output of the up- and down-stream thermopiles by the monitored output. Experimental results show that the normalization is quite useful for achieving a range as wide as 1:1000 and also for reducing the temperature and pressure dependence.