Photoelectric Fork sensors SR21 Series

Datasensing SR21 Series

The SR21 Series provides a premium family of slot-type photo-electric sensors, engineered for extremely fine detection, high-speed response, and compact integration in automated packaging and printing applications. With a slot width of just 2 mm, a minimum detectable object/gap of ~0.5 mm, response time as low as ~20 µs, and switching frequency up to 25 kHz, this series delivers exceptional precision, high throughput, and reliable performance on moving webs, labels and transparent materials. 

Design & Functionality

• The sensors feature a robust metal housing (Zamak) measuring approximately 20 × 26 × 90 mm, optimized for machine-side mounting in print, label or packaging equipment. 
• Optical and operational characteristics include:
  • High switching frequency of 25 kHz and a very low response time (~20 µs) — enabling detection of fast moving labels or parts with minimal delay. 
  • Narrow 2 mm slot width and minimum detectable object/gap of approx. 0.5 mm, providing ultra-fine edge detection capability. 
  • Available in IR (infrared LED) emission version for hole/label detection, and Red/Green LED emission version (RG) for print registration mark detection on transparent or coloured films. 
  • Automatic threshold setting via a push-button (AUTO-SET) or dynamic setting during label movement, simplifying setup and maintenance. 
  • Selectable output logic (NPN or PNP), selectable Light-On/Dark-On mode, and compatible with standard 4-wire M8 connector (4-pole) for flexible installation.
  • Operating voltage 10 … 30 V DC, no-load supply current ≤ 55 mA, output current up to 100 mA, output saturation voltage ≤ 2 V. 

Total Crossed Beams

(In this slot sensor context, “Total Crossed Beams” is used metaphorically to emphasise the sensor’s full detection coverage along the narrow slot rather than literal crossed beams.)

• The SR21 Series ensures a stable detection zone across the slot aperture even when labels or print marks vary slightly in position, size or speed — resulting in fewer missed signals, greater repeatability, and higher installation reliability in high-speed lines.
• The combination of ultra-narrow slot (2 mm) and high switching performance makes it especially suited for applications where precision, speed, and minimal physical footprint** are required — such as high-speed label applicators, transparent film print mark detection, and packaging registration systems.

Beam Pitch Options

(Here interpreted as variant options (IR or Red/Green emission) rather than literal beam spacing.)

• Example variant: IR version — infrared LED emission, optimal for detection of holes, labels or continuous surfaces. 
• Example variant: RG version — red/green LED emission, designed for print registration mark detection on transparent materials. 
• These options allow you to select an SR21 model that matches your application’s target contrast type, background material and detection speed — offering design flexibility.

Intrinsic Synchronism

• The emitter, detector, electronics and configuration interface are fully integrated in one compact housing — no external synchroniser modules required — which simplifies wiring, reduces installation complexity, and aids in compact machine integration.
• With built-in AUTO-SET push-button, output/ready LEDs and compact metal body, the SR21 supports fast commissioning, easy adjustment, and reliable diagnostics — making it well suited for maintenance-sensitive environments.

Operational Advantages

• Ultra-fine detection capability: With a slot width of 2 mm and detection of items/gaps down to ~0.5 mm, the SR21 Series provides high precision edge detection suited for printing and labelling.
• High throughput performance: With switching frequencies up to 25 kHz and response times around 20 µs, the sensor keeps pace with fast web, label or packaging equipment.
• Compact footprint with industrial robustness: Metal housing, M8 connector, IP65 protection and robust mechanical design make the series ideal for machine-side mounting on demanding production lines.
• Applications: Ideal for label presence/absence detection, print or registration mark detection on transparent films, gap detection between labels or parts, high-speed packaging conveyors, and any installation requiring narrow slot sensor, high switching speed, and extreme precision.