How do I select the right automatic sampler for my process?

 

This is a good place to start this blog as its a question we are often asked by our clients, and it’s an important one to understand. If you are taking a sample from a dynamic process it is important that the sample you take is representative of the batch or the production over a period. Representative sampling is the act of capturing a small volume of material from a process that reflects the characteristics of the entire batch or process stream.

 

A manual scoop or bucket sample just give the user an insight into the process at one particular point. So this would be called a grab sample and depending on the process conditions a grab sample may not be suitable due to segregation or separation. There are also dangers around taking a manual grab sample from the process, especially of the material is moving or in an open vessel for example. We often come across customers running their entire process from small grab samples taken using a tin cup or scoop. This can lead to mis information on what is actually happening in the process and also cause the loss of yield due to over drying or mixing issues. There is also an environmental hazard with manual sampling especially for powders or chemicals that can be exposed to the atmosphere, or create dust and fumes.

 

The most accurate way of sampling is to sample more frequently with smaller volumes therefore building a composite sample of the process over 1 hour, or 1 day for example. There are also sample carousels available that will allow the user to take a sample over a period into one container, then indexing to a new container for a different period. A good example of this would be on a continuous process where you have a sampler collecting a 1 litre composite every hour in 100 ml samples, indexing to a new jar for each subsequent hour. at the end of the 24 hour period the client has 24 composites of each hours production.

 

 

The common types of sampler come in 3 forms. A spot sampler which enters the process extend to a spot in the stream (typically at 10%) and sample from that spot. This would be the least representative of automatic sampler unless the product is homogenous, but in some non homogenous processes it is the only way available. The next type of sampler would be a Strip sampler, these types of samplers either stroke into the process (60% into the stream) and remove a strip as it retracts. By capturing a strip across the entire width of the stream of material it captures a far more representative sample. The 3rd sampler type and the ultimate would be a full cross cut sampler, this type of sampler will stroke across the entire stream and capture a full 100% cut of the process stream. The cross cut sampler can also be configured to take a composite over time building a profile of the entire production.

 

The selection of which sampler you can use in your process will be very dependent on the location you would like to take a sample and also the material to be sampled. We can assist you with this selection of course but to give you an idea. Typically liquid and slurry samples are homogenous so a spot or strip sample is sufficient in these types of material, normally a spot sampler like the Sentry Isolok is a good choice for this type of application. Powders in pneumatic conveyors are not homogenous but its also difficult to fit a full cross cut sampler in these locations, so then a strip sampler would be used like the Sentry model RX. If the material is in a gravity chute or exiting a hopper and is free falling, this would be ideal for a full cross cut sampler like the Sentry model SA. Conveyor belts are also an area of interest and samplers are typically fitted in the head chute of the conveyor where the material is falling for the best accuracy.

 

It is very important to have the right type of sampler in the right location to give you a representative idea of your process. This will provide you with reliable and accurate analysis results, will help you save money by reducing waste and downtime, protect your operators and the environment, and ensure product quality and regulatory compliance. You can also get yield improvements and process optimisation which all add to savings.

 

Samplers can be controlled either by a PLC or an automatic controller from Sentry equipment. The controller or PLC can be configured to trigger the sampler actuation at a set interval and for it to be active for a set period. The sampling cycle can also be changed dependent on the time of day or week. You can also take other process inputs such as the ending of a batch process to trigger the sampling cycle.

 

As always you can contact us directly via our web site or live chat, or simply call us on +612 9486 3501. JWII have specialised in process automatic sampling since 1982 so we have a great knowledge of the type of sampler and how and where to apply it to a particular process. We would be more than happy to answer any questions you may have.