The best use of an analyzer is realized once the instrument is properly calibrated to the customer’s quality parameters and ranges. It’s important to realize that there are two phases to the calibration process, the first is static calibration with reference standards and the second is a dynamic calibration using dynamic comparative data. Each phase is discussed below:
This calibration can be used to quantify analyzer accuracy and precision with a set of static reference standards that approximate the customer’s range of quality. If being used to validate performance the standards (typically a set of five standards that have been designed to represent as closely as possible the customer’s quality ranges) are run in the analyzer for an hour each and the data is used to calibrate the analyzer. With the analyzer calibrated the standards are run again to validate performance. If care has been taken to configure the standards in a manner that represents the typical belt loading, the static calibration should deliver results that are close to correct also for dynamic operation. This may break down because the customer’s actual dynamic flow varies too much. But it should be noted that in order to dial in the dynamic calibration, dynamic comparative data is necessary. This is discussed in section 2 below.
The Standards. The static referenced standards used for static calibration can have very different origins. One approach preferred by many customers is to utilize materials from the customer’s site to build the standards. For example, in the case of a cement plant the customer will gather rock in such a way that it represents the quality ranges experienced in normal operation of the cement plant. The advantage in this approach is that the material used for calibration exactly represents the material the analyzer will be seeing and therefore provides the most effective calibration. The challenge in this approach is to obtain samples of the material for analysis in the lab that correctly represent the quality of the samples. In addition, it can be a challenge to ensure the material is homogeneous within the samples. The material also needs to be crushed to a level that accommodates insertion in the sample containers, typically abs plastic tubing three and one half inches in diameter and forty inches long – from 10 to 30 per set. A very different second approach also preferred by many customers is to specify to SABIA the desired quality ranges for the standards and have SABIA manufacture a set of synthetic standards that are used during manufacture and are shipped with the analyzer to be used for calibration in the field. These standards are typically two-kilogram plastic bags filled with elemental powders. Depending on the application the number of two kilogram bags would be as few as 30 bags or as many as 100. Each bag is approximately eight inches by eight inches and about one inch thick, double bagged six mil clear plastic.
Dynamic calibration takes advantage of existing systems within the customer’s operation for acquiring samples that are representative of the process. In the case of coal it would be a mechanical sampling system, often times located at or near the coal loadout. In the case of cement it would be the sampling system typically located at the exit of the raw mill. There are some simple keys to successfully acquiring good dynamic comparative data. Simply put, ensure that the sampling frequency is such that the quality population of the sample properly represents the process and ensure that the analyzer and the sampler are looking at the same population. Accomplishing the latter simply means ensuring that timing devices are synchronized and that time delays between the analyzer and sampler are taken into account. Even though it can take a long time for material to make its way through a raw mill in cement it is surprising how accurate the dynamic calibration can be. Often it is the case that the visibility given by a SABIA analyzer enables a customer to correct a host of problems in the operation such as biased sampling systems, intermittent plugging, fugitive material events and other such difficulties.
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