Reducing the additional error caused by the time‐difference method in transit‐time UFMs

In transit‐time ultrasonic flow meters (UFMs), one of the most commonly used methods in the time domain is the cross‐correlation method which is a time‐consuming and high computational requirement approach. Hence, the time‐difference approaches are preferred to reduce the computational requirement and increase the response time. However, the time‐difference methods in comparison to conventional ones have been suffering from an additional bias error (ABE). In this study, using a numerical simulation method, the ABE is analysed and some effective factors such as pipe diameter, flow velocity and medium temperature are introduced. Then, an approach for removing or reducing the ABE is presented. Since the time‐difference method has been used for Mach numbers <0.1, it is shown that by using a second‐order approximation, this method can be used for Mach numbers of more than 0.1, and the ABE resulting from this method is reduced to nearly zero. An experiment has been carried out on a 6 in transit‐time UFM with an eight‐path x ‐configuration to verify the validity of the second‐order approximation method. The test results confirm that the proposed method can be successfully used in UFMs with the flow velocity greater than Mach 0.1.