A method for measuring the quantity of fluid received by the detection device is disclosed. The method comprises the following steps:- connecting the detection device (2) to an inlet tank (4)- filling a quantity of fluid (46) from the inlet tank (4) into the detection device (2), wherein the quantity of fluid (46) exceeds a predefined volume- closing an outer valve (12) and flooding a portion of the detection device (2) hereby evacuating/removing the air in this portion of the detection device (2)- detecting the fluid level (L1) in the flooded portion of the detection device (2).The method comprises the step of filling fluid (46) into a gas separator (24) and detecting the fluid level in the gas separator (24).The method comprises the step of:- opening the outer valve (12) and filling a further quantity of fluid (46) from the inlet tank (4) into the detection device (2), while detecting the flow and/or volume of the fluid (46)- emptying the inlet tank (4)- closing an outer valve (12) and flooding a portion of the detection device (2) hereby evacuating/removing the air in this portion of the detection device (2) and- detecting the fluid level in the flooded portion of the detection device (2).The method comprises the step of applying one or more pumps (18, 20) to transport fluid (46) into and/or within the detection device (2).The method comprises the step of determining the pressure at both sides of a pressure difference inducing member (28) provided in the detection device (2), wherein the method further comprises the step of determining the flow (Q1, Q2) at each side of the pressure difference inducing member (28), and applying the pressures and flows at both sides of the pressure difference inducing member (28) to calculate the gas content of the fluid (46).
