a result a very accurate representation of flow conditions within the flow meter can be obtained the dimensions of the sensor support structure are such however that a relatively large opening is required as shown in fig6 to enable the insertion and removal of the structure into the flow meter body an alternative arrangement which does not require such a large opening as illustrated in fig7 to 10 referring to fig7 a support structure 21 is mounted in a flow meter body 22 sandwiched between flanges 23 and 24 of a pipeline a meter installation adapter 25 is fitted upstream of the body 22 as in the case of the embodiment of fig1 to 6 the adapter is accurately located relative to the body 22 by virtue of the co operation of formations provided on the body and adapter flanges in particular fig7 shows a portion 26 projecting from the adapter flange as it is engaged in a radial slot in the periphery of the body flange the support structure 21 differs from that shown in fig3 to 6 however in that rather than being circular it is only part circular so as to define what may be loosely described as a j shape such an arrangement can be manoeuvred into position through a much smaller opening in the body 22 than is required to receive the full ring sensor structure as shown in for example fig5 fig8 9 and 10 illustrate in.