Measurement xxx (xxxx) xxx Please cite this article as: I.S.B. Ferreira, Measurement, https://doi.org/10.1016/j.measurement.2020.108681 Available online 2 November 2020 0263-2241/© 2020 Elsevier Ltd. All rights reserved. Measurement system analysis in angle of repose of fertilizers with distinct granulometries I.S.B. Ferreira a , R.S. Peruchi b, * , N.J. Fernandes a , P. Rotella Junior b a College of Engineering and Management, Federal University of Goi´ as, 1120 Dr. Lamartine Pinto de Avelar Avenue, Catal˜ ao, GO 75704-020, Brazil b Department of Industrial Engineering, Federal University of Paraíba, Campus I, Jo˜ ao Pessoa, PB 58051-900, Brazil A R T I C L E INFO Keywords: Repeatability Reproducibility Angle of repose Fertilizers ABSTRACT This research presents an experimental study for measurement system analysis of angle of repose in fertilizers with variable granulometry (1.5 mm < d50 < 5.0 mm). In the literature, there are different procedures for determining this angle of repose, which often result on a variety of measurements for one measurand. Thus, the main objective of this work is to propose a method for measurement system validation of angle of repose. The statistical validation was based on Nested Gage Repeatability and Reproducibility (NGR&R) and the experiment was conceived through a technical apparatus built to measure the angle of repose of fertilizers. Experiments was conducted by using available resources in a typical industrial laboratory of fertilizer characterization. Among the measuring procedures, the fxed funnel has been used and an image analyzer software has been adopted to gather the data. The experiment was planned with 3 (three) operators, 10 (ten) samples with distinct granulometries and 3 (three) replicates. The result analysis has shown that the measurement error through the frst measuring procedure was deemed unacceptable. After investigating the root cause of measurement error, a new standard measurement procedure was proposed. The new procedure was able to measure the angle of repose precisely, reducing measurement error from 59.93% to 4.82%. 1. Introduction Granular materials are of great importance in many industrial pro- cesses; however their complex behaviors are still poorly understood [1]. The challenges of handling granular materials arise when materials are agitated, as they do not behave as stable and solid materials [2]. In addition, stress distribution in granular materials is unevenly distributed along the power chains [3], which depend on the particles’ interactions and on the arrangement packing to stabilize. The fuidity of these granular materials depends on a set of parameters, mainly, the angle of repose [4]. The angle of repose is defned as the slope measured at their base of a pile of granular solids, uncompressed, after having taken place the runoff [5]. In the fertilizer industry the angle of repose of granular materials has been widely studied, as it is a very important macroscopic parameter in characterizing the fowability of granular materials [6]. The angle of repose is necessary to consider the storage capacity and design of hop- pers, rails, conveyors, among others. The literature review indicates that the angle of repose can also be used in other felds such as agriculture (designing silos), pharmacology (drug production and fuidity), geology (monitoring of sand dunes), bulk material handling, mining, civil engi- neering and numerical model calibration [7]. There are different procedures for determining the angle of repose. Beakawi and Baghabra [7] cite fve ways of physically determining the angle of repose: (1) tilting box method, (2) fxed funnel method, (3) revolving cylinder/drum method, (4) hollow cylinder method and (5) tilting cylinder method. Even though there are several guidelines and procedures, they lack of standardization [8]. Rouse [9] compared six different procedures for measuring the angle of repose taking six different types of granular soils. The results showed that each procedure and granular materials produced different measurements. As a result, the measuring procedure should be chosen according to the granular material. Rackl and Hanley [10] observed that within the same measuring procedure, high measurement variation can occur with respect to repeatability (i.e., the measuring error of an operator under the same operating conditions) and reproducibility (i.e., the measuring error between different operators or others operating conditions). Ac- cording to W´ ojcik et al. [11], there is no universal procedure for * Corresponding author. E-mail addresses: isabelengenharia@gmail.com (I.S.B. Ferreira), rogerioperuchi@ct.ufpb.br (R.S. Peruchi), nilsonfernandes@ufg.br (N.J. Fernandes), paulorotela@ct.ufpb.br (P. Rotella Junior). Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement https://doi.org/10.1016/j.measurement.2020.108681 Received 21 May 2020; Received in revised form 17 October 2020; Accepted 27 October 2020