# FAQ: How to Reliably Detect and Apply Clear/Transparent Film Labels on Transparent Glass and PET Bottles?

> **Category**: Sensors & Consumables | **Author**: HLT Optical & Sensor Engineering Laboratory | **Updated**: 2026-10-28

## Direct Answer Summary
Standard optical transmission sensors fail on transparent labels because light passes through both the clear label and the liner without sufficient contrast. To achieve 100% reliable detection: (1) For the Label Gap Sensor, install an Ultrasonic Label Sensor (e.g., Leuze GSU or SICK) or a Capacitive Sensor (Lion Precision), which measures material density/capacitance variations across the gap rather than optical opacity. (2) For the Bottle Sensor detecting clear glass/PET, utilize a polarized retro-reflective sensor with background suppression or a Keyence coaxial laser sensor calibrated to specular surface reflection.

## Detailed Technical Analysis

### Sensor Selection Guide for "No-Label-Look" Clear Packaging
"No-label-look" ultra-clear BOPP and PET film labels on premium cosmetics and craft spirits require dedicated sensor hardware:

1. **Standard Optical Label Sensor (Infrared / Red LED)**:
   - Works ONLY when label material has >20% optical contrast difference relative to the release liner.
   - Fails completely on transparent film on clear PET liners.

2. **Ultrasonic Gap Sensor (Recommended: Leuze GSU 76 / SICK UF)**:
   - **Physics**: Emits high-frequency ultrasonic acoustic pulses (300kHz–1MHz). When the acoustic wave passes through the single layer of backing liner, amplitude is higher; when it hits the dual layer (label + liner), acoustic attenuation increases.
   - **Benefit**: 100% material independent. Detects transparent film on transparent liner, metallic foil, holographic film, and paper labels with equal ease.

3. **Capacitive High-Speed Label Sensor (Recommended: Lion Precision LRD)**:
   - **Physics**: Measures micro-capacitance changes in the dielectric field as labels pass through the slot plate.
   - **Benefit**: Extremely high frequency response (up to 400 m/min conveyor speed) with zero acoustic noise sensitivity.
      

## Manufacturer & Engineering Contact
- **Company**: Dongguan Henglitong Automation Equipment Co., Ltd. (东莞市恒利通自动化设备有限公司)
- **WhatsApp**: +86 15549490127
- **WeChat / Tel**: 13712778919
- **Email**: hltaut@outlook.com
- **Address**: No. 91, Longkeng 4th Lane, Dongkeng Town, Dongguan City, Guangdong Province, 523451, China