Yesterday, we looked at calibration of Coriolis mass flow meters in natural gas applications and mentioned piecewise linearization (PWL), but did not delve into it. Let’s do with today’s post.I found a presentation by Emerson’s Tonya Wyatt, Fine Tuning Coriolis Flow Meter Calibrations Utilizing Piece-Wise Linearization. The PWL calibration method basically looks at the flow rate at points over its operating range and applies a multi-point piecewise linear interpolation correction to the “as-found error”.
This correction is applied at selected linearization points and is equal and opposite to the average of the as-found values at the same flow rate. The correction values applied between neighboring points are determined by linear interpolation between the two points. Corrections above the highest flow rate are held constant. Also, the correction below the lowest point is based on linear interpolation to zero error at zero flow to allow the meter zero adjustment to control accurately below the flow rate at time, t (Qt).
PWL calibration and configuration is conducted by qualified third-party calibration laboratories selected and hired by end users. The basic procedure used is to first install and zero the meter. Next, collect the as-found data with pressure compensation active. After this step, select and program the Coriolis meter with up to 10 linearization points from the as-found data. Finally, collect the as-left data to verify the accuracy of the linearization.
Contact Emerson’s Micro Motion team for more about this testing and qualified calibration laboratories. Also, visit the Micro Motion section of Emerson.com for additional resources and tools to find the right flow meter for your application.
You can also connect and interact with other flow experts in the Flow group in the Emerson Exchange 365 community.