On BM series meters one complete turn of the screw alters the calibration by approximately 0.1% while similar rotation on LBM meters alters the calibration by 0.23%. The unit comprises a stepless friction wheel and disc, the ratio being adjusted by means of a calibration screw.
Reference has been made to a calibrating mechanism interposed between the rotor shaft and readout counter. A turndown ratio as high as 100:1 is claimed in some designs.įigure 52. Cumulative flow quantity and instantaneous flow rate are indicated, and these meters are suitable for in-vehicle use. Crankshaft rotation is transmitted magnetically to a pulse output flow transmitter. Several designs of positive-displacement (volumetric) fuel gauges make use of a four-piston metering unit with the cylinders arranged radially around a single-throw crankshaft. The process fluid must be clean because they operate with small clearances particles greater than 100 µm must be filtered out upstream of the unit. Their main disadvantage is the appreciable pressure drop required to drive the metering unit, which may approach 1 bar. Their accuracy is not affected by pulsating flow and many designs do not require a power supply nor lengths of straight pipe upstream and downstream in their installation. Positive-displacement meters provide high accuracy, ☐.1% of actual flow rate is claimed, and good repeatability. Rogers, in Engine Testing (Fifth Edition), 2021 Positive-displacement flowmeters