Product packaging is often made of lightweight polymeric foams or plastic sheets and films. These materials are relatively inexpensive, but manufacturers still want to minimize waste and maximize yields. Across high volumes of low-cost materials, even a small per-unit savings can become significant, especially as the price of petroleum  – a key ingredient in many polymers – continues to rise. For companies with environmental sustainability efforts, there are other important considerations as well.

The excessive use of packaging materials can contribute to environmental pollution, especially with polymers that are slow to degrade. Yet, materials such as plastic sheets and films can’t be too thin. Otherwise, they’re subject to tearing, puncture, and other forms of failure. The manufacturers of these and other packaging materials need to achieve the optimal thickness, and buyers need to know that what they’re ordering can meet the required specifications.

Precision measurement systems that use capacitance can help manufacturers to determine the proper thickness of closed cell foams and many plastics. By better controlling the amount of packaging material that is used, manufacturers can contribute to reductions in both operational and environmental waste without sacrificing quality. Companies gain better control of their current material costs as they look for ways to incorporate packaging made of compostable and biodegradable polymers.

Capacitive Measurement for Packaging Materials

Capacitive measurement systems consist of probe-based capacitive sensors, fixtures, an amplifier, probe holders and cables. Capacitance, the ratio of the change in an electric charge to the corresponding change in its electrical potential (voltage), is formed between a probe and a grounded target and varies as a function of the distance (gap) between them. To measure non-conductive materials such as plastics or foams, a metal ground plate can be used as one of the targets.

The sensing element in the capacitive probe emits an electric field that passes through the non-conductive material to the ground plate. The thickness of this insulating material can be determined from its dielectric constant, a numerical value that describes a material’s ability to store electrical energy in an electrical field. The dielectric constant of the non-conductive material affects the capacitance between the two conductors: the capacitive probe and the plate.

Putting a sheet of foam or plastic between the capacitance probe and ground plate causes a measurable change in capacitance. Different thicknesses of the same non-conductive material produce differences in capacitance, and these differences can be measured with nanometer precision. The probe’s capacitive sensors then send signals to an amplifier that outputs a voltage proportional to the thickness of the measured material.

The connection between the probe and amplifier can be wired or wireless. Analog amplifiers require wired connections and cost less. Digital amplifiers are more expensive but protect data integrity in noisy environments while eliminating the need for analog-to-digital conversion. Digital amplifiers can also achieve extremely high resolution and can support wireless connections.

Why Saint-Gobain Uses MTI’s Digital Accumeasure

Saint-Gobain, a French multinational manufacturer of high-performance materials, was seeking a better way to measure closed-cell foams because its method of producing accurate and repeatable measurements was time-consuming and cost-prohibitive. Saint-Gobain worked with MTI Instruments of Albany, New York (USA) to install a capacitance-based Digital Accumeasure, which is ideal for obtaining position, thickness, or dynamic measurements for non-conductive materials on an assembly line.

To learn more about Digital Accumeasure technology, check out this product information and watch this YouTube video about capacitance measurement for dielectric materials. If you’re ready to discuss your measurement application, contact MTI Instruments.