lindab | we simplify construction Flow measuring unit - circular FRU Technical data Settings V nom indicates the measuring range for the actuator. A standard FRU is calibrated to V nom of 7 m/s according to the table below. In special cases the FRU can be set to a higher V nom , e.g. 10 m/s. The output signal from VRD3 is linear between 2-10 V which corresponds to a flow between 0 and V nom . Air flows corresponding to air velocities below 1,2 m/s will result in a 2 V signal. (Zero flow). Air flow measurement The accuracy of air flow measurement depends on the flow conditions in front of the measuring cross. It is preferable to have a long straight duct section in front of the measuring point, according to the table below. If these recommendations are not followed, it will cause an unstable air flow measurement and therefore higher inaccu- racy in the regulation of the required air flow. Components Bend Tee-piece Damper Recommended straight duct before unit 3 x Ød 2 x Ød 6 x Ød With recommended straight duct in front of the unit, the air flow accuracy will be according to the table below. Duct velocity > 3 m/s 1,2 - 3 m/s Air flow accuracy +/- 5% +/- 10% FRU nominal air flow ( V nom ) Size Ød nom mm 100 125 160 200 250 315 400 500 630 (Standard) V nom (7m/s) m 3 /h l/s 198 55 309 86 506 141 791 220 1236 343 1963 545 3165 879 4946 1374 7851 2181 2 Lindab reserves the right to make changes without prior notice 2021-01-06
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