Compression Force to Weight Relationship on a tablet press
Tablet weight changes can be detected and controlled by monitoring compression force.
A tablet press can be instrumented with a strain gauge that senses and reacts to compression force changes. Compression force fluctuation is the result of slight changes in tablet weights. It is normal and expected that powder blends are not perfectly uniform, this fluctuation is detected by checking tablet weights during compression. When tablet weights change they typically trend, either increasing or decreasing in average tablet weight. As the tablet weights increases the compression force increases and as tablet weights decrease the compression force decreases.
As blended powders are being compressed there is a consistent and measurable force rhythm that is detected using a strain gauge. The strain gauge sends a signal to control the volumetric powder fill level (weight adjustment cam), which controls tablet weights. Thus we have created a loop; the amount of force to compress is really reporting tablet weight. The controls can be setup to react to the compression force changes and adjust the weights within a range or stop the press. If the amount of force is too much or not enough this is directly attributable to tablet weight, provided that the press is being operated correctly and all parts and components are in good operating condition.
When using an automatic weight control device it is important to note that changes to press settings like thickness, speed, force feeders, and pre-compression can be misinterpreted by the force monitor. Proper steps must be followed to prevent improper operation. Then acceptable tablet weight ranges are established so that off weight tablets are rejected.