Precision Thickness Measurement
Thickness is a key parameter for many manufacturers as it affects the functionality, quality and cost of finished products.
Functionality- Raw material thickness directly influences the physical properties of a product. Important examples include;
- Tensile strength of textiles, plastic films, paper and tissue.
- Rigidity of plastic film, cardboard packaging.
- Barrier properties of plastic films.
- Puncture resistance of plastic microwaveable containers.
- Opacity of inks, coatings, plastic film and paper.
Quality- Thickness should be controlled to ensure batch consistency and ensure products have the correct tactile “feel”.
- High quality goods are packaged in robust high gauge materials.
- Quality toilet tissue, baby wipes, kitchen paper are supplied thicker and stronger.
- Thicker, heavier paper is used for certificates, brochures and art supplies.
Cost-Using a low accuracy gauge inevitably leads to in the supply of goods that are above or below thickness tolerance.
- Out of tolerance material can be rejected by customer leading to huge re-working costs and loss of credibility.
- A few microns saving in reduced thickness can equate to tens of thousands of Dollars/Pounds/Euros of raw material savings in a relatively short period.
The FT3 thickness gauge allows product to be manufactured within tight tolerances targeted right in the middle of a customer’s specification.
- The high accuracy and resolution give absolute confidence that material is always supplied within customer requirements.
- A high confidence in results often allows tighter manufacture control and a reduction in raw material use. Raw material savings can pay for the gauge in a matter of weeks or months.
- Securely date and time stamped result labels can be attached to retained samples or job sheets giving absolute confidence that a product has been tested throughout its production run.
How does the FT3 achieve high precision?
Sensor-The FT3 is uses a precision LVDT displacement sensor with highly stable electronics to produce a very sensitive transducer system.
Measurement Parameters-The key to repeatability and accuracy is to tightly control all the parameters that can lead to measurement uncertainty.
The parameters that effect thickness measurment are;
- Measurement pressure.
- Presser foot profile and size.
- Measurement velocity.
- Parallelism of presser foot to measurement plate.
- Dwell time.
To allow manufactures in the same industry sector to measure using the same conditions, these key measurement parameters are often specified by international standards (ASTM/ISO etc.).
External Factors-External effects such as temperature change and vibration will affect measurment, the FT3 instrument is designed to reduce the impact of these.
Calibration– The FT3 has a multi-point calibration routine to reduce/eliminate the effect of non-linearity in the LVDT sensor.
Electronic Drift– The 0.01micron resolution instrument includes routines to reduce the effects of short term thermo-electronic drift of <0.1 microns.
Why do different applications have different measurement parameters?
Measurement Pressure– Many materials including plastic film, plastics, rubber may crush or deform dependent on the pressure applied during testing and the momentum of the presser foot.
Textiles require high pressures during testing to remove wrinkles and airgaps.
Tissue thickness testing demands a light measurement pressure and slow presser foot speed so the paper fibre are measured without being crushed and flattened.
It is clear that different industries have adopted measurement parameters that give meaningful results for their own application.
FT3 measurement forces are applied using fixed masses; each instrument is supplied ready apply the exact force specified in the relevant international standard.
The FT3-V variable pressure thickness gauge can be useful if a sample needs to be tested to more than one standard, it can also be used to determine the compressibility of samples under different conditions.
Measurement foot size and profile-The measurement head size and profile is usually determined by the ISO Standard for the material.
- Domed measurement head- Small areas can be measured with high resolution- Plastic films and coatings.
- Small diameter flat measurement heads- used to apply a large pressure in a small area- Paper and board applications.
- A large diameter flat foot- Measures the average thickness of fibrous material over a large area with light pressure- Tissue Paper. Opacity of inks, coatings, plastic film and paper.
Measurement velocity– The speed of the measurement head can also have an effect on thickness measurement. A fast moving head will impact a sample with more energy and may deform or dent the material.
The measurement velocity of FT3 head can be set by the user from 1 to 5mm/sec. This speed is sometimes specified in international standards.
The most significant source of measurement error in any system is often introduced by the human operator.
The FT3 family of instruments have a number of features that reduce the impact of human operator.
Fully automated operation– the main parameters are fully controlled by the instrument; measurement pressure, speed and dwell time.
On board statistical calculation-Mistakes are often made in transcribing results and calculating statistics, these functions are performed automatically by the instrument.
Results can also be output via RS232 to SPC programs, lab networks or MS Excel.
QA labels record results throughout the batch – Securely time and date stamped labels with statistical results can be produced throughout a batch run and attached to job card or retained samples. This traceable control gives the customer confidence that the whole batch of product is within specification and allows manufacturers to issue certificates of conformance.
Standards of Conformity
The FT3 family of instruments comply to a variety of ISO & ASTM standards for many different appplications including:.
Plastic Film – BS 2782-6, DIN 53370, ISO 4593, ASTM D6988
Paper & Board – ISO 534, ISO 3034, DIN 53105, BS EN 20534, BS 4817, TAPPI T411, SCAN P7, SCAN P31, FEFCO No 3,
Tissue – ISO 12625, BS 7387, SCAN P47
Textile – ISO 5084e.