In solid and powder sampling applications, it is important to obtain a representative sample with a sampler that enters the material stream, captures a quantity of that material, and extracts a representative sample for analysis. For all solids and powders, the sampler chosen is determined by the material flow rate, the sample amount required, and the material characteristics such as flow behavior, the shape and makeup of the particles, and the tendency of the solid or powder to segregate or group together.
Because the top layer contains larger particles, and finer particles tend to migrate towards the bottom, the particle segregation means the scooping method yields an inaccurate sample.
In solid and powder sampling, segregation is an issue, and can get worse as the particle size distribution increases: Fine particles vibrate and move into the spaces between larger particles, forcing the large particles to rise to the top of the container over time. Because the top layer contains larger particles, and finer particles tend to migrate towards the bottom, the particle segregation means this scooping method yields an inaccurate sample. A better method is to take a sample of mixed material or take a strip sample of free-flowing materials as they are moving or pouring.
A flour miller in New Jersey had been taking hand samples of product from a valve located in the side of the transport line. Personnel would take a product sample manually three times per batch for quality control purposes, with the first sample determining whether to continue running the process. This method was labor- and time-intensive and was not yielding a representative sample, as the sample was gathered from the inside edge of the pipe only.
The milling operation chose to implement two Sentry® SA/A automatic cross-cut samplers, which take a cross-cut sample of free-flowing materials from vertical spouts and chutes. How it works: A solenoid-controlled pneumatic rotary actuator swings a pelican type diverter on an arc across the entire product flow. The diverter captures a sample and then discharges it through the pelican tube. This sampler features a design approved by the USDA, Canadian Grain, FGIS, and NOPA.
In this application, the customer chose to obtain samples of finished product before it was conveyed to either packaging or truck loading. The samplers were mounted directly below the mixers and above the metal detectors followed by the rotary valve for the pneumatic transport line. This new method of sampling using the Sentry SA/A sampler allowed the facility to automatically gather a complete cross-section of the powder product with each sampling instance.
By utilizing the Batch option on the sampler controller, the facility was able to collect three composite samples per hour with a constant volume that was representative of the process over the course of the elapsed time.
Sample automation was controlled by the Sentry SBC sampler controller. With this method, the operator can gather the first required sample by pressing the “Grab” key as many times as required to collect the needed sample volume. The operator then changes the container and places the sampler controller in “Auto” and utilizes the “Batch” option. This allows the sampler to collect sample automatically at a rate of one instance every 2 minutes for the next 20 minutes. By utilizing the Batch option on the sampler controller, the facility was able to collect three composite samples per hour with a constant volume that was representative of the process over the course of the elapsed time. Using this option reduced waste and the chance of over-filling the sample container, which could result in wasted product or a potential spill.
This sample automation technique provided a representative sample. The facility managers and operators felt assurance that this automatic sampling method was a much better and more accurate way of sampling – and they noted that they could be more confident in the quality of their product because of it.