Full-Scale Error and Setpoint Error in Flow Control

The accuracy of a flow controller is usually represented as a percent of full-scale flow (%FS), which means when a flow controller is operated at its rated full-scale flow rate, it achieves maximum accuracy. Accuracy is represented as a percent of setpoint, and is significantly reduced when the flow controller is operated at lower flow rates.

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For instance, a 1000 cc/min flow controller with a +/- 1% FS accuracy and operating at a setpoint of 1000 cc/minute can be deemed to be accurate to +/- 1% of the setpoint. However, if operated at a setpoint of 100 cc/min, the accuracy represented as a percent of setpoint is reduced to +/- 10% of the setpoint.

Flow Controllers

The flow controllers from Environics instruments are calibrated to an accuracy of +/- 1% of setpoint, and not full-scale. In other words, the accuracy of the flow controller is the same, irrespective of the operating point of the flow controller. An 11-point calibration of each flow controller in the instrument is carried out to achieve this accuracy.

This graph shows a comparison of the percent setpoint error of an Environics instrument using calibrated flow controllers with that of a standard uncalibrated flow controller.

full scale error

environics

This information has been sourced, reviewed and adapted from materials provided by Environics, Inc.

For more information on this source, please visit Environics, Inc.

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