Through-beam photoelectric sensors consist of an emitter and a receiver in separate housings. The emitter sends a beam of light to the receiver, which determines a target is present when the beam is interrupted. All information about the E20827 at a glance. We assist you with your requirements. ✓ Technical data ✓ Mounting and Installation Instructions ✓ CAD drawings ✓ Compatible AccessoriesThrough-beam sensors from Balluff serve to detect objects reliably, regardless of surface, color, material - even with a heavy gloss finish. When an object interrupts the light beam, this causes a change in the. One fibre optic cable emits light from the sensor. What Is a Photoelectric Sensor? What Is a Photoelectric Sensor? Photoelectric Sensors.