• Jan 08, 2026
• Color Sensor
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The photoelectric mark sensor (also called a registration mark sensor or “electric eye”) is a key component in packaging machines.
It detects printed registration marks (color marks) on the film to control film indexing, ensuring accurate print-to-cut alignment and consistent bag length.

During production, the film may slip, stretch, or drift due to tension, rollers, or material changes. By continuously reading the marks, the sensor helps the machine compensate for these shifts, reducing misregistration (off-center prints or wrong seal/cutoff positions).

Printed film should include registration marks (color marks). The sensor detects each mark and tells the machine when to stop running the film, so the seal and cut happen in the correct position relative to the printed artwork.

Accurate registration ensures consistent bag length, particularly for printed bags with stringent design tolerances.

These sensors come in several versions—most commonly single-color (monochrome), dual-color (two-channel), and three-color (RGB) models.
The key differences are detection capability, film/print compatibility, and resistance to interference (e.g., reflective films or complex backgrounds).

We no longer offer the single-color (monochrome) model.

1. Overview of Key Differences

Item	Dual-Color Model	Three-Color Model
Light source	2 colors (commonly red + green or red + blue)	3 colors (red + green + blue, RGB)
Detection principle	Compares reflectance/contrast in two channels	Compares the reflectance/contrast in two channels
Anti-interference ability	Moderate	Strong
Registration mark requirement	Usually requires higher contrast marks	More tolerant of low-contrast or complex backgrounds
Recommended print/film complexity	Low to medium	Medium to high
Cost	Lower	Higher
Setup & adjustment	Typically simple setup	May require more tuning

2. Selection Recommendations (Practical)

The most direct deciding factor is print complexity.
In most cases, the more complex the printed film/artwork, the more we recommend a three-color (RGB) mark sensor. Other factors usually have a much smaller impact.

• Simple, high-contrast registration mark + clean background → Dual-color is usually sufficient
• Busy artwork / multiple colors / gradients / reflective films → Three-color (RGB) recommended
• Frequent artwork changes → Three-color (RGB) helps reduce the risk of sensor mismatch and saves troubleshooting time

If you’re not sure which type you need, send us your film artwork/design (or a photo of the printed roll). We’ll review it and recommend the right sensor model.