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.
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.
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.
This information has been sourced, reviewed and adapted from materials provided by Environics, Inc.
For more information on this source, please visit Environics, Inc.