What Is a Light Barrier? Types and Selection Criteria
A light barrier is an area-scanning optical sensor that monitors parallel beams from a transmitter bar with a receiver bar opposite and gives an output when a beam is interrupted.
A light barrier is an area-scanning optical sensor that monitors whether the many parallel beams from a transmitter bar reach the receiver bar opposite, and gives an output when one of the beams is interrupted. It is used to detect irregularly shaped or position-varying objects that a single-beam photoelectric sensor might miss, and for passage, presence and height monitoring on conveyor lines and at material passage points.
Photoelectric sensor, light barrier and safety light curtain
| Device | Beams | What it detects | Personal protection |
|---|---|---|---|
| Through-beam photoelectric sensor | Single beam | An object crossing the line of the beam | No |
| Light barrier (automation) | Multiple beams | An object passing anywhere through the scanned area | No |
| Safety light curtain | Multiple beams | A hand, finger or body entering | Yes, in types certified to IEC 61496 |
The light barriers in the catalog are automation types. The product data shows no safety certification; they cannot replace a safety light curtain for operator protection in hazardous zones such as presses and robot cells.
Selection criteria
- Protection height: Chosen by the height of the opening to be scanned. The catalog offers 25 cm, 30 cm, 50 cm, 75 cm and 1 m.
- Beam spacing and smallest object: The smallest object to be detected must be larger than the gap between two beams; otherwise it can pass between them. Check the beam spacing in the product datasheet.
- Operating distance: The distance between transmitter and receiver must stay within the range given in the datasheet.
- Supply and output: The catalog models have a 24 V DC supply and a PNP NC output. With an NC output, the output is active while the beams are clear; the signal drops when a beam is interrupted or the cable breaks. Set up the PLC program accordingly.
- Communication: The built-in RS-485 and analogue module pass barrier data to the control system over serial communication or an analogue signal, not only as an on/off signal. Check the datasheet for which data is transmitted.
Installation and common mistakes
- Using it for safety: An uncertified barrier does not meet the legal and technical requirements for operator protection.
- Misaligned mounting: Transmitter and receiver must be at the same height, parallel and facing each other. On vibrating frames, a loose bracket shifts the alignment and causes false outputs.
- Mounting near shiny surfaces: Stainless sheet, glass or glossy painted surfaces can reflect the beam around the object to the receiver; keep the barrier away from them.
- Mounting two barriers side by side facing the same way: One transmitter's beam can reach the other receiver. On neighbouring barriers, swap the transmitter and receiver positions or leave a gap between them.
- Neglecting lens cleaning: Dust, steam and oil weaken the beam. Route the connection cable away from power cables; suitable cables are in the Sensor Connectors and Cables category.
Light barriers in the catalog
The Light Barriers category has 5 active products, all from the Isıso ISCB-GB series: 24 V DC supply, PNP NC output, built-in RS-485 and analogue module, yellow housing.
| Model | Protection height |
|---|---|
| Isıso ISCB-GB12 | 25 cm |
| Isıso ISCB-GB16 | 30 cm |
| Isıso ISCB-GB24 | 50 cm |
| Isıso ISCB-GB36 | 75 cm |
| Isıso ISCB-GB48 | 1 m |
If single-beam detection is enough, see the Photoelectric Sensors category.
Frequently asked questions
Is a light barrier the same as a safety light curtain?
No. Both use multiple beams, but a safety light curtain is protective equipment certified to IEC 61496. The light barriers in the catalog are for automation detection only.
How do I choose the protection height?
Measure the height of the opening the object can pass through and choose the model that covers that height completely.
What does a PNP NC output mean?
The output switches the positive side (+24 V) and is active while the beams are clear. When a beam is interrupted or the cable breaks, the output drops, so a cable fault also shows up as a detection and gets noticed.