An apparatus for sensing a flow of fluid , the apparatus comprising: a flow sensing device comprising: a heating structure having a centerline that defines upstream and downstream sections of the flow sensing device ; a membrane structure ; a first thermopile , wherein at least a portion of the first thermopile is disposed over the membrane structure , and wherein the first thermopile comprises: a first plurality of upstream thermocouple junctions disposed over the membrane structure , and a second plurality of upstream thermocouple junctions offset from the membrane structure ; and a second thermopile , wherein at least a portion of the second thermopile is disposed over the membrane structure , and wherein the second thermopile comprises: a first plurality of downstream thermocouple junctions disposed over the membrane structure , and a second plurality of downstream thermocouple junctions not disposed over the membrane structure , characterised in that a maximum temperature difference is defined by a minimum temperature difference location located upstream of the centerline and a maximum temperature difference location located downstream of the centerline ; wherein the first plurality of upstream thermocouple junctions is aligned substantially parallel to the centerline along an upstream vertical line through about the minimum temperature difference location, and wherein the first plurality of downstream thermocouple junctions is aligned substantially parallel to the centerline along a downstream vertical line through about the maximum temperature difference location. a flow sensing device comprising: a heating structure having a centerline that defines upstream and downstream sections of the flow sensing device ; a membrane structure ; a first thermopile , wherein at least a portion of the first thermopile is disposed over the membrane structure , and wherein the first thermopile comprises: a first plurality of upstream thermocouple junctions disposed over the membrane structure , and a second plurality of upstream thermocouple junctions offset from the membrane structure ; and a first plurality of upstream thermocouple junctions disposed over the membrane structure , and a second plurality of upstream thermocouple junctions offset from the membrane structure ; and a second thermopile , wherein at least a portion of the second thermopile is disposed over the membrane structure , and wherein the second thermopile comprises: a first plurality of downstream thermocouple junctions disposed over the membrane structure , and a second plurality of downstream thermocouple junctions not disposed over the membrane structure , a first plurality of downstream thermocouple junctions disposed over the membrane structure , and a second plurality of downstream thermocouple junctions not disposed over the membrane structure , characterised in that a maximum temperature difference is defined by a minimum temperature difference location located upstream of the centerline and a maximum temperature difference location located downstream of the centerline ; wherein the first plurality of upstream thermocouple junctions is aligned substantially parallel to the centerline along an upstream vertical line through about the minimum temperature difference location, and wherein the first plurality of downstream thermocouple junctions is aligned substantially parallel to the centerline along a downstream vertical line through about the maximum temperature difference location. <EOS>