PT ZONE: Performance Measurement

Stefan Kalt - Bio
Stefan Kalt recently joined K-Tron as Global Business Development Manager Plastic Compounding & Extrusion. More (+)
Jaime Gómez - Bio
Jaime Gómez is the Global Business Development Manager for Chemicals and Plastics for K-Tron. More (+)

MOST RECENT CONTENT: Performance Measurement

The Anatomy of Feeder Performance – Photo/Graphic TBDAs a major contributor to formulation quality and consistency, feeder performance rightly deserves close attention and concern.

Measurement Procedures

Whether performed automatically or manually, precise sampling is crucial to accurate performance measurement.

Defining Repeatability – RepeatabilityRepeatabilityThe performance statistic most familiar to feeder users, repeatability quantifies the degree to which a feeder’s discharge stream varies over brief time intervals, producing a snapshot of one dimension of feeder performance.Note that the repeatability measurement says nothing at all about whether the feeder is delivering, on the average, the targeted rate (that is the purpose of the linearity measure performed on a properly spanned feeder). Repeatability does, however, reveal a great deal about the expected extent of short-term flow-rate inconsistencies, an important contributor to the integrity of the formulation and end-product quality.The repeatability measurement is performed by taking a series (usually at least 30) of carefully timed consecutive catch samples from the discharge stream, weighing each, and then calculating the + standard deviation of sample weights expressed as a percentage of the mean value of the samples taken.

Repeatability Timescales – Timescale GraphicAn issue of growing importance in the specification and measurement of feeder repeatability relates to catch sample duration.

Defining Linearity – Linearity GraphicAssuming a properly spanned feeder (a calibration scaling process resulting in measured and requested feed rate being equal at a specified operating rate), a feeder’s linearity measurement quantifies how well it delivers, on the average, the targeted discharge rate throughout the feeder’s complete operating range.Perfect linearity is represented by a straight-line correspondence between the setpoint and measured average feed rate throughout the feeder’s specified turndown range from its design full-scale operating rate.(4942 placeholder)To perform a linearity measurement, several groups of timed catch samples must be taken from the feeder’s discharge stream.

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Performance Measurement


Performance Measurement

How is feeder performance measured? This section introduces you to the metrics of repeatability, linearity, and stability as applied to feeder performance. Also discusses considerations of process timescales and how it impacts feeder performance and the quality of your end product.

The core task of every feeder in plastics application is to precisely, accurately and consistently control discharge rate to comply with the processor’s applicable process specifications and end-product quality standards.

But how exactly is feeder performance expressed, how can it be measured, and how can processors evaluate feeder performance in the plant? This section explains what goes into a complete expression of feeder performance, what it means, why it’s so important to your operation, and how to measure and monitor feeder performance.

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