Hi Caroline. The first ...

Hi Caroline. The first consideration isn't the type of meter but whether or not the pipe flows full bore or not. Usually sewers are not full bore which means neither meter types will work unless especially manufactured (i.e. mag flow) to work in part full pipes. ABB manufactured a version some years ago. A pipeline section can be designed and modified to ensure that a short section remains full at all times, then either will work and a mag low can easily be installed during this work. Ultrasonics can be retrofitted externally providing that the bore (as in working condition diameter) is known and the pipe material is made from a homogenous material. These considerations are OK for most sewers but if yours is an exceptionally large diameter then ultrasonics may be the better option however the pipe stills needs to be flowing full bore. Alternatively if not full bore have you considered depth measurement, e.g. capacitance tubes, to provide data for calculation into a flow estimate?