A method for detecting an air bubble or liquid in a flow tube of a fluid flow system, the method comprising: monitoring a first output signal of a force sensor of the fluid flow system for a change from the first output signal to a second output signal, wherein the change from the first output signal to the second output signal comprises at least one of a change in amplitude of an Alternating Current, AC, component of the first output signal and a change in a signal level of a Direct Current, DC, component of the first output signal; detecting the change from the first output signal to the second output signal, wherein the change in the amplitude of the AC component is detected based on an increase or a decrease of the amplitude of the AC component, and the change in the signal level of the DC component is detected based on a shift of the signal level from a first signal level to a second signal level; determining one of a time duration of the second output signal of the force sensor from an instance the first output signal is changed to the second output signal, and a number of transitions corresponding to changes in consecutive signal levels of the DC component from the first signal level to the second signal level; comparing the time duration of the second output signal with a predefined time and the number of transitions with a predefined number of transitions; and when one of the time duration of the second output signal exceeds the predefined time, and the number of transitions of the DC component exceeds a predefined number of transitions: determining that the change from the first output signal to the second output signal is in response to one or more of an uncontrolled sensor position, or movement of the flow tube, and determining a threshold, wherein the threshold is determined based on a predefined percentage of the second output signal. monitoring a first output signal of a force sensor of the fluid flow system for a change from the first output signal to a second output signal, wherein the change from the first output signal to the second output signal comprises at least one of a change in amplitude of an Alternating Current, AC, component of the first output signal and a change in a signal level of a Direct Current, DC, component of the first output signal; detecting the change from the first output signal to the second output signal, wherein the change in the amplitude of the AC component is detected based on an increase or a decrease of the amplitude of the AC component, and the change in the signal level of the DC component is detected based on a shift of the signal level from a first signal level to a second signal level; determining one of a time duration of the second output signal of the force sensor from an instance the first output signal is changed to the second output signal, and a number of transitions corresponding to changes in consecutive signal levels of the DC component from the first signal level to the second signal level; comparing the time duration of the second output signal with a predefined time and the number of transitions with a predefined number of transitions; and when one of the time duration of the second output signal exceeds the predefined time, and the number of transitions of the DC component exceeds a predefined number of transitions: determining that the change from the first output signal to the second output signal is in response to one or more of an uncontrolled sensor position, or movement of the flow tube, and determining a threshold, wherein the threshold is determined based on a predefined percentage of the second output signal. determining that the change from the first output signal to the second output signal is in response to one or more of an uncontrolled sensor position, or movement of the flow tube, and determining a threshold, wherein the threshold is determined based on a predefined percentage of the second output signal.