How Target Flow Meters Work
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Target Flow Meters How Target Flow Meters Work Target flow meters measure flow by measuring the amount of force exerted by the flowing fluid on a target suspended in the flow stream. The force exerted on the target by the flow is proportional to the pressure drop across the target. Similar to differential pressure flow meters, Bernoulli’s equation states that the pressure drop across the target (and hence the force exerted on the target) is proportional to the square of the flow rate. Using this relationship, 10 percent of full scale flow produces only 1 percent of the full scale force. At 10 percent of full scale flow, the target flow meters accuracy is dependent upon the transmitter being accurate over a 100:1 range of force. Transmitter accuracy is typically degraded measuring low forces in its range, so flow meters accuracy can be similarly degraded. Therefore, this non-linear relationship can have a detrimental effect on the accuracy and turndown of target flow meters. Remember that of interest is the accuracy of the flow measurement system --- not the accuracy of the transmitter. |
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