Datalogic Label & Fork Sensors for Accurate Label Gap Detection
SR21, SR23 and SRF sensors for labellers, print-and-apply systems and part detection.
On a labelling machine everything depends on one tiny signal: the moment the gap between two labels passes the sensor. A Datalogic label sensor catches that gap on every label, so each one lands straight and in the same place — no skipped products, no double labels. Below we explain how fork sensors work, which Datalogic model suits which label material, and how to install one so it stays reliable shift after shift.
Label Sensor or Slot Sensor — Which Do You Need?
Label (fork) sensor
A narrow fork with the emitter in one arm and receiver in the other. The label web runs through the slot and the sensor sees the change in light between label-plus-liner and liner only. Datalogic SR21 and SR23 belong here.
Slot sensor
A wider fork for detecting objects that pass through the gap — tabs, edges, teeth on a wheel or small parts on a feeder. The Datalogic SRF series is built for this.
Choose the Right Emission for Your Labels
| Label and liner | Recommended | Why |
|---|---|---|
| Paper labels on paper or glassine liner | SR21-IR / SR23-5-IR-PH | Infrared passes through paper well and gives a strong label/gap difference |
| Printed, coloured or dark labels | SR21-RG | Red/green light gives better contrast where infrared sees little change |
| Transparent labels on transparent liner | Ultrasonic or capacitive sensor | Optical difference is too small — ask us for a suitable model |
| Parts, tabs or edges through a wide gap | SRF-50 / SRF-80 / SRF-120 | Wider fork for objects, not the label web |
Datalogic Label & Slot Sensors in Stock
Datalogic SR21-IR
Infrared fork label sensor, M8
Rs. 8,690
Datalogic SR21-RG
Red/green fork label sensor, M8
Rs. 15,895
Datalogic SR23-5-IR-PH
Infrared, PNP, external teach
Rs. 9,960
Datalogic SRF-50-5-N
SRF slot sensor, NPN
Rs. 9,500
Datalogic SRF-80-5-P
SRF slot sensor, PNP
Rs. 10,500
Datalogic SRF-120-5-N
SRF slot sensor, NPN
Rs. 12,500
Installation Checklist
- Run the web through the middle of the fork. Keep the liner centred between the arms and away from the fork base so flutter does not change the reading.
- Keep the web tight. Mount the sensor just before the peel plate, where the web tension is steady.
- Teach with the real material. Teach on the liner (gap) and on the label, using the same roll that will run in production.
- Check the output at full speed. One clean pulse per label means the setting is right; missed or double pulses mean it needs a re-teach.
- Use the right connector. SR21 and SR23 use an M8 connector — order the matching cordset with the sensor.
Where Datalogic Label Sensors Are Used
Bottle and jar labellers
Front, back and wrap-around labelling in FMCG, pharma and cosmetics.
Print-and-apply systems
Shipping and batch labels applied at conveyor speed in logistics.
Pharma serialisation
Accurate label placement before inspection cameras check the code.
Tag and ticket feeders
Counting and positioning tags, tickets and die-cut parts.
Label Sensor FAQs
What does a label sensor do on a labelling machine?
It detects the gap between self-adhesive labels on the backing liner. The labeller uses that signal to stop the web so each label is dispensed at exactly the same position on the product.
What is the difference between the SR21-IR and SR21-RG?
Both are high-resolution fork label sensors with an M8 connector and PNP/NPN output. The SR21-IR uses infrared light, which passes well through paper liners; the SR21-RG uses red/green light, which helps with printed or coloured labels where infrared gives too little difference.
Can a photoelectric label sensor detect transparent labels?
Clear labels on a clear liner often give almost no optical difference. For those, an ultrasonic or capacitive label sensor is usually the reliable choice — send us your label sample details and we will suggest a suitable model.
When should I choose an SRF slot sensor instead of an SR21?
SR21 and SR23 are narrow label forks for the label web itself. SRF slot sensors are wider fork sensors used to detect parts, edges, tabs or teeth passing through the slot — for example on feeders, conveyors or rotating discs.
Why does my labeller dispense two labels at once?
Usually the gap was not detected: the sensor needs re-teaching for the current liner, the web is not running through the middle of the fork, or the sensor is too slow for the machine speed.
Tell Us About Your Labels
Share the label material, liner type, label size and machine speed. We will recommend the right Datalogic label or slot sensor and quote from ready stock.
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