When you're protecting an automatic door, a gate, or a movable machine guard, the sensor you choose makes the difference between reliable operation and a shutdown every time something gets too close. Two very different options cover opposite ends of the safety sensor spectrum: the EMX Industries IRB-MON 2 thru-beam photo eye and the Schmersal BNS33-11ZG-2128 safety magnetic sensor with magnet actuator. One watches for objects crossing an invisible beam; the other confirms that a guard is closed by matching a coded magnet to a reed switch array. Which one you need depends on whether you're stopping motion or proving position.
Quick Verdict
If you're protecting a door, gate, or barrier from someone or something entering while it's moving, the EMX Industries IRB-MON 2 thru-beam photo eye is the straightforward choice. If you need to interlock a movable machine guard or an articulating robot arm so the machine cannot run unless the guard is closed, the Schmersal BNS33-11ZG-2128 safety magnetic sensor with actuator is the one to use.
At a Glance
| Product | Listed Price | Working Principle | Best For |
|---|---|---|---|
| EMX Industries Thru-Beam Photometer Sensor IRB-MON 2 photo eye | USD 45.00 | Monitored infrared beam between transmitter and receiver | Entrapment protection on doors, gates, and barriers |
| SCHMERSAL SAFETY MAGNETIC SENSOR BNS33-11ZG-2128 with Magnet Actuator 101148482 | USD 215.00 | Coded-magnet reed switch interlock with matching actuator | Guard position interlocking on movable machine guards and robot arms |
Where Each Product Wins
The EMX wins when the task is presence detection along an opening. Its IRB-MON 2 is described as a monitored, weather-proof thru-beam photo eye that is UL325 compliant and housed in an IP65-rated enclosure for indoor or outdoor use. The kit includes a transmitter, receiver, integrated protective hoods, and a removable lens sunshield, and it is compatible with a wide variety of monitored operators as well as most non-monitored legacy products.
The Schmersal wins when the task is proving that a guard is actually closed. The BNS33-11ZG-2128 is a coded-magnet sensor with a matching actuator, sealed to IP67, wired for 24 VDC, and terminated with an M8 4-pin connector. It's made in Germany and mounted to a chassis, so it suits safety interlock circuits on moving guards and robot arms.
Product Notes
EMX Industries Thru-Beam Photometer Sensor IRB-MON 2 photo eye
If your concern is entrapment protection on an automatic door, gate, or barrier, this IRB-MON 2 photo eye gives you an all-in-one kit. It is a monitored, weather-proof thru-beam infrared sensor with a transmitter and receiver, plus integrated hoods and a removable lens sunshield. Its IP65 housing is suitable for indoor and outdoor use, and because it is UL325 compliant, it can work with a wide variety of monitored operators. The design is also compatible with most non-monitored legacy products, which can simplify retrofits. What holds it back: it detects a broken beam, not guard position, so it will not confirm that a movable machine guard is closed. If your safety circuit needs that confirmation, you need a guard interlock instead of a photo eye.
SCHMERSAL SAFETY MAGNETIC SENSOR BNS33-11ZG-2128 with Magnet Actuator 101148482
When a movable guard or articulating robot arm has to be proven closed before the machine can operate, the BNS33-11ZG-2128 is the better fit. This set includes the reed switch sensor and the coded-magnet actuator; the reed switches are wired in series and close only when they see the matched magnetic field array. It's sealed to IP67, so it can withstand submersion, and it operates on 24 VDC with an M8 4-pin connector and a cable termination. The thermoplastic enclosure and chassis mounting make it straightforward to place on a guard frame. The tradeoff is the price gap between this interlock and a photo eye, along with the New - Open box condition, meaning the package has been opened rather than factory-sealed. This is an interlock, not a presence sensor, so don't expect it to detect objects moving through an opening.
Final Choice by Use Case
- For an automatic door, gate, or barrier where you need entrapment protection and want a weather-proof photo eye that comes with transmitter, receiver, hoods, and sunshield, go with the EMX IRB-MON 2.
- For a movable machine guard or articulating robot arm where the safety circuit must verify that the guard is closed, go with the Schmersal BNS33-11ZG-2128 with its matching magnet actuator.
