The temperature compensation of a thermal flow sensor by changing the slope and the ratio of resistances

Abstract The errors of fluid temperature in Wheatstone-bridge circuit result from a variable gap between Rh and Rf (or Rh′). Rf is changed by fluid temperature and Rh is changed by Wheatstone-bridge equilibrium. So, the gap varies in response to temperature of the fluid. The gap can be constant; the error of temperature can be solved. This paper suggests two compensation methods that maintain the gap constant in response to the temperature change of fluid. To maintain the gap constant between Rh and Rf, there are two methods. The first method is by changing the slope of Rh in the calculating method. The second one is by changing the slope of Rf in adjusting the ratio of the resistances. Changing the slope of Rh is needed to measure it in a circuit and to calculate the compensated Rh. It needs to know voltage and current within a circuit in real time, but changing the slope of the Rf is easy to compensate in a circuit by adjusting the ratio of the resistances.