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Part of the Omron Photoelectric Sensors series — see the full model table, lifecycle status and replacement parts.

Omron E3T-ST21 2M — front view of the 18.5 x 7 x 9.5 mm square through-beam emitter (or receiver) showing the red 650 nm LED lens window, the orange operation indicator LED and the M2 mounting screw hole on the side of the PBT housing

Omron E3T-ST21 2M — Through-Beam Photo Sensor, 300 mm

SKU: E3T-ST21 2M

USD 44.00

Omron E3T-ST21 2M through-beam photo sensor, 300 mm, NPN Light-ON, M2 mount, 2 m cable. In stock, China shipping.

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Product Overview

The Omron E3T-ST21 2M is an ultrathin through-beam photoelectric sensor from the E3T series, manufactured by Omron Corporation. Hengyixin Automation ships this sensor from our Xiamen warehouse with a 30-day DOA return window and a datasheet PDF included in the box.

The sensor consists of an emitter and a receiver facing each other across a 300 mm gap. It detects opaque objects 2 mm or larger at 1 ms response. Output is NPN open-collector, Light-ON, rated 26.4 VDC max at 50 mA max. Supply is 12 to 24 VDC +-10% (ripple p-p 10% max). The red LED at 650 nm makes alignment visible to the eye during commissioning.

The square body is 18.5 (H) x 7 (W) x 9.5 (D) mm, made of PBT with a denatured polyarylate lens. Mounting uses M2 screws. Connection is a 2 m pre-wired PVC cable. The E3T-ST11 2M sibling is the side-view NPN Light-ON with the same 300 mm range; the E3T-ST12 2M is the PNP Light-ON sibling.

Key Features

  • E3T-series ultrathin through-beam sensor, square top-view housing, 300 mm sensing distance, 2 mm min detectable opaque object
  • NPN open-collector output, Light-ON, 26.4 VDC max at 50 mA max, residual voltage 1 V max below 10 mA
  • Red LED 650 nm light source, 1 ms operate / reset response, 12 to 24 VDC +-10% supply
  • PBT housing with denatured polyarylate lens, 18.5 x 7 x 9.5 mm, M2 mounting, IP67, 2 m PVC cable
  • SKU: E3T-ST21 2M
  • Series: Omron E3T-series ultrathin photoelectric sensor with built-in amplifier
  • Voltage: 12 TO 24 VDC

Best-Fit Applications

  • Semiconductor wafer cassette index where 2 mm opaque object detection through a narrow gap is required inside a cleanroom robotic end-effector
  • Small component drop-check on a blister packaging line where 1 ms response verifies parts falling through a sorting chute without slowing the conveyor
  • Spare replacement on a medical-device assembly tool where the previous ultraminiature photo-eye has reached end of life on a sterile washdown station

Buying Checklist

  • Pick the E3T-ST21 2M for an ultrathin through-beam NPN Light-ON sensor at 300 mm in a 7 mm wide housing for tight-mounting cleanroom or medical tooling.
  • Pick the E3T-ST12 2M instead when the wiring is PNP sourcing for the same 300 mm range and 7 mm housing.
  • Pick the E3T-ST11 2M instead when the same square 7 mm housing is needed but the controller expects Dark-ON instead of Light-ON logic.

Technical Specifications

Manufacturer Omron Corporation (Japan)
Series Omron E3T-series ultrathin photoelectric sensor with built-in amplifier
Model / SKU E3T-ST21 2M
Sensing Method Through-beam type, separate emitter and receiver
Sensing Distance 300 mm
Standard / Min Object Opaque, 2 mm diameter minimum
Light Source Red LED, 650 nm
Supply Voltage 12 to 24 VDC +-10% (ripple p-p 10% max)
Current Consumption Emitter 10 mA max, receiver 20 mA max (30 mA max total)
Control Output NPN open collector, 26.4 VDC max, 50 mA max, residual voltage 1 V max below 10 mA, Light-ON
Response Time 1 ms max operate or reset
Environment / Mounting IP67, -25 to 55 C operating, 35 to 85% RH, 18.5 x 7 x 9.5 mm body, PBT housing, M2 mounting screws, 2 m PVC cable

FAQ for E3T-ST21 2M

What is the Omron E3T-ST21 2M used for?
It is an ultrathin through-beam photoelectric sensor for small-object detection in tight mounting spaces. The 7 mm wide housing fits between conveyor rails or inside robotic end-effectors where standard M18 photo-eyes do not.
What is the minimum detectable object size?
An opaque object 2 mm in diameter or larger. Anything translucent or below 2 mm will not reliably break the 300 mm beam at the rated supply voltage.
E3T-ST21 vs E3T-ST11 - what is the difference?
The E3T-ST21 is the top-view (square) Light-ON version. The E3T-ST11 2M is the side-view Light-ON version of the same family with the same 300 mm range and NPN output. Pick the 21 for top-aim mounting and the 11 for side-aim.

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