Technology guide · Film, sheet & coated webs
X-Ray Transmission Web Gauging
See how much material is on the web while the line is running. X-ray transmission gauging converts a calibrated transmission signal into basis weight, helping you follow variation across and along production.
For thickness, coating add-on or density, the measurement needs the right material information and sensor arrangement. Start with the result you need to control.
Understand the signal
From transmitted intensity to basis weight.
An X-ray source sends a beam through the web. The detector measures how much reaches the other side. Material in the beam reduces that signal through absorption and scattering.
Measure the transmission
The detector captures the transmitted intensity for the selected beam geometry and acquisition settings.
Calibrate for the material
A material-specific calibration relates attenuation to mass per unit area. Composition and X-ray energy affect that relationship.
Follow the production trend
Compare the calibrated result with the product target and limits, then decide whether an operator or control system should respond.
Basis weight means mass per unit area. It is commonly reported in g/m². A thickness value in µm requires density information or a separate geometric measurement.
Technical resources: NIST attenuation fundamentals.
Specify the result
Four useful outputs, with different measurement requirements.
| Output | What it tells you | What the system needs |
|---|---|---|
| Basis weight | Mass per unit area of the material in the beam. | A qualified calibration for the composition and measurement range. |
| Calculated thickness | Thickness derived from basis weight and density. | An appropriate density value that represents the measured material and process state. |
| Net coating weight | The mass added by a coating or process stage. | A suitable substrate baseline or coordinated measurements before and after the addition, with matched calibrations. |
| Calculated bulk density | Mass per unit volume. | Calibrated basis weight and an independent physical-thickness measurement for the same material and location. |
Swipe to see all columns.
For consistent units: thickness (µm) = basis weight (g/m²) ÷ density (g/cm³). Use the coating’s net mass and density when calculating coating thickness.
What if the recipe changes?
Changes in fillers or composition can change attenuation. Changing bulk density also changes the relationship between basis weight and thickness. Define which properties may vary so the measurement can distinguish process variation from a changed material response.
Coating & lamination
Separate the material you add from the web beneath it.
A reading through a coated web includes the substrate and the coating. To report net coating weight, establish which contributions are known and which must be measured separately.
On a multi-station line, synchronized measurements help compare corresponding web locations. Scantech SameSpot aligns scanner trajectories so substrate variation is less likely to appear as a change in coating add-on.
Choose the measurement positions around the process: incoming substrate, wet coating, dry coating or final laminate. Account for line travel, drying and the layers present at each station.
Plan a web coating measurement system →
Wet and dry coating weight answer different questions. Specify the production state and whether the result is for one side, both sides or the complete laminate. Verify subtraction and location matching on the actual line.
Turn the profile into a decision
See the variation, then define the response.
A traverse builds a profile over time.
As the scanner crosses a moving web, it follows a diagonal measurement path. The resulting cross-direction profile helps reveal broad variation across the width; it is not automatically a measurement of every point on the roll.
Response time has several parts.
Sensor averaging, beam footprint, traverse time and web speed determine what variation is captured. Control also depends on transport delay and how quickly the actuator and process respond.
Software makes the result usable.
FLEXSCAN brings profiles, trends and production views together. Define recipes, alarms, records and plant interfaces around the operator’s tasks.
Explore Scantech FLEXSCAN software →
Need automatic correction?
A measured profile can feed a compatible control system. For a flat die, that means mapping the profile to actuator positions and agreeing on the controller, hardware and tuning. Machine-direction control is a separate control task.
Explore automatic thickness profile control →See a production roll-report example
Choose by the measurement requirement
Where do other gauging methods fit?
Compare the required output, material range and line conditions. The right choice depends on the application and the configured instrument.
| Method | Useful measurement role | What to check |
|---|---|---|
| X-ray transmission | Calibrated basis weight; derived thickness or coating add-on using the required material data and gauge configuration. | Composition, range, beam geometry, calibration and measurement positions. |
| Beta / gamma transmission | Established transmission methods for suitable basis-weight and thickness applications. | Performance at the actual range, source and service requirements, integration and the condition of existing equipment. |
| Infrared | Selected material, moisture or layer measurements when absorption signatures allow them to be distinguished. | Material spectra, substrate response, calibration and the properties that may change. |
| Optical thickness | Surface-position or geometric-thickness measurements using an appropriate laser or confocal arrangement. | Surface and optical response, alignment, access and passline stability. |
Swipe to see all columns.
Replacing an isotope gauge?
Review what the existing gauge controls, which interfaces must remain and how the replacement will be calibrated. The new X-ray gauge uses an electrically generated source, without a sealed radioactive isotope.
Explore beta and gamma gauge replacement →Apply the measurement
Choose the application that matches your production line.
Review the product profile, material recipe and required control response.
Define net add-on, substrate tracking and the appropriate scanner positions.
Separate coating loading, physical thickness and calculated density.
Relate total basis weight to reinforcement, resin addition and process state.
Inside Amcor’s Extrusion Line
See a Scantech customer example involving a line upgrade, coordinated measurements and production control.
It is a useful view of how the measurement fits into a working converting line.
Battery production measurement
Explore Scantech’s overview of online measurement for battery production lines.
Use the electrode application page to work through the outputs and sensor positions needed for your process.
Common questions
X-ray web gauging FAQ.
Does X-ray directly measure thickness?
The detector measures transmitted intensity. Calibration converts attenuation into basis weight. Thickness can then be calculated using suitable density information, or measured independently with a compatible geometric-thickness sensor.
Can one gauge separate every layer in a laminate?
Not generally from one total-transmission value. Identify the unknown layers and the required result, then select the measurements, material information and calibrations needed to resolve them.
Does a scanner inspect the entire web surface?
A traversing gauge builds a sampled profile as the web moves. If the objective is continuous visual-defect coverage, consider a dedicated web inspection system alongside the dimensional or basis-weight measurement.
Can X-ray be useful when density varies?
Yes, when the required result is basis weight and the composition and calibration support it. Converting that result to thickness needs suitable density information. Combining basis weight with an independent thickness measurement can support calculated bulk density.
Is an X-ray gauge radiation-free?
No. It generates ionizing radiation while energized, although it does not use a sealed radioactive isotope source. Shielding, interlocks and applicable installation requirements remain part of the system design.
Where should I start when selecting equipment?
Start with the web gauging systems page. Share the web construction, width, speed, measurement range and the production decision the result needs to support.
Technical resources: Scantech coating and lamination · Scantech customer examples.
Application review
Make the measurement useful to your line.
I’ll help define the required output, review scanner placement and connect the measurement to your operator, records or control system.
Helpful details to send
- Material composition, layer structure and changing recipes
- Web width, line speed and available installation space
- Basis-weight or thickness range and tolerance
- The required output: total web, net coating, thickness or density
- Existing gauges, software interfaces and control equipment
A drawing, part photo or sample description is a useful starting point.