The thought that ...

The thought that electromagnetic flow meters also have a non-contact working way,or  magnetic flow meters have a lower request to straight pipe installing section. is wrong. Actually,  ultrasonic flow meters can get the accuracy of 5% and there are two basic types of ultrasonic meters - transit-time and Doppler meters. Transit-time meters send ultrasound signals into the flow using transducers that are either clamped onto or inserted into the pipe at two locations.  Ultrasonic meters use the frequency of 1 MHz, which is not even close to the frequency for acoustic noise. When mag meters measure very small flows it is done on the basis of very little voltage. When you measure very little voltage, you will be more vulnerable to electric noise.  As a result, these types of meters are somewhat nonlinear, especially at low flow rates, which necessitate the use of flow corrections. For small dimensions, ultrasonic meters only measure the middle part of the flow, which is where the velocity is the highest. It is, therefore, necessary to correct for the part of the flow that is not covered.