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Omron E3FA-RP21 M18 retro-reflective photoelectric sensor — front view showing the M18 ABS plastic body with the polarized red 624 nm LED transmitter/receiver lens on the front face, the operation indicator (orange) and stability indicator (green) LEDs visible on the rear

Omron E3FA-RP21 — M18 Retro-Reflective, 4 m, PNP, MSR, M12

SKU: E3FA-RP21

USD 16.50

M18 cylindrical ABS plastic retro-reflective photoelectric sensor with polarized MSR (mirror-surface rejection), red 624 nm LED, PNP open-collector output, M12 4-pin connector, 4 m sensing range with E39-R1S reflector, IP67/IP69K.

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Product Overview

The E3FA-RP21 is the polarized retro-reflective variant of Omron's E3FA cylindrical M18 photoelectric sensor family — an ABS plastic housing with a built-in polarized MSR (mirror-surface rejection) filter that distinguishes real targets from shiny reflections. The 'retro-reflective' detection principle uses a reflector (E39-R1S, sold separately) on the opposite side of the detection zone — the sensor detects the beam reflected from the reflector; when any target (opaque or reflective) breaks the beam, the sensor switches.

Decoding the E3FA-RP21 model number

The E3FA family naming: E3FA = M18 cylindrical ABS plastic housing family (vs E3FB = M18 nickel-brass housing for rugged applications, E3RA = right-angle / radial version, E3RB = nickel-brass right-angle); R = Retro-reflective (vs D = Diffuse, T = Through-beam); P = PNP open-collector output (vs N = NPN, so E3FA-RN11/RN21 are NPN versions); 21 = M12 4-pin connector (vs 11 = 2 m pre-wired cable, 12 = short pigtail with M12, etc.). The 'MSR' (mirror-surface rejection) is built-in and indicated by the polarized LED + filter combination. Common pickings: E3FA-RP11 2M (PNP pre-wired retro-reflective with MSR), E3FA-RN21 (NPN M12 connector), E3FA-RP22 (300 mm range retro-reflective M12), E3FB-RP21 (nickel-brass M12 housing).

The MSR / polarized filter — why shiny targets would fail without it

Standard retro-reflective sensors emit red light and detect red light returning from the reflector. The trouble: any shiny object (a stainless-steel bracket, a glass bottle, a wet painted surface) also reflects red light back to the sensor, producing a false trigger. The MSR (mirror-surface rejection) polarization filter solves this: the sensor emits polarized red light (rotated 90° from horizontal). Light reflecting from the E39-R1S corner-cube retroreflector preserves this polarization (rotated 180°), so it passes through the filter at the receiver. Light reflecting from a shiny surface reverses the polarization (becomes horizontal again), so it gets blocked by the filter.

4 m sensing range with E39-R1S reflector

The E39-R1S reflector (40 × 60 mm corner-cube reflective tape or plastic) gives a 4 m sensing range with the E3FA-RP21. The E39-R1S is sold separately and must be ordered alongside the sensor. For longer range up to 6 m, use the E39-R2 reflector (80 × 80 mm large-area). For shorter range with smaller reflector footprint (e.g., tight installations), use the E39-R3 (15 × 30 mm small reflector). The polarized MSR filter costs ~30 % of the sensing distance vs non-polarized retro-reflective (where 7 m is typical with E39-R1S on E3FA-RP-1 7m max), so the trade-off is range for shiny-target filtering.

Key Features

  • M18 cylindrical ABS plastic housing
  • Retro-reflective with MSR
  • Red 624 nm LED, polarized for shiny-target rejection
  • PNP open-collector output, Dark-ON / Light-ON selectable
  • M12 4-pin quick-disconnect connector
  • 4 m sensing distance with E39-R1S reflector
  • 100 mm minimum sensing distance
  • Response time 0.5 ms
  • SKU: E3FA-RP21
  • Series: E3FA M18 Cylindrical Photoelectric Sensor
  • Voltage: 2 V

Best-Fit Applications

  • Glass bottle counting on a bottling line — E3FA-RP21 with E39-R1S reflector at the fill-station trigger point; the MSR filter.
  • Aluminum can detection on a canning line — sensor detects cans passing the trigger point; polarized filter rejects the highly-reflective.
  • Wet food product detection on a reflective stainless-steel conveyor — sensor detects wet bottles or pouches without false triggers from.
  • Shiny plastic toy detection on an automated assembly conveyor — the toy has molded shiny surfaces; standard retro-reflective would false-trigger.

Buying Checklist

  • Pick E3FA-RP21 for M18 plastic retro-reflective with MSR, PNP, M12 connector, 4 m with E39-R1S
  • Pick E3FB-RP21 for M18 nickel-brass housing — pick for machine-tool coolant or food-processing washdown environments
  • Pick E3FA-RP11 2M if you need pre-wired cable instead of M12 connector — pick for fixed installations
  • Pick E3FA-RN21 for NPN output — pick for legacy NPN/sinking PLC inputs
  • Pick E3FA-DP21 if your target is near the sensor — pick for diffuse detection without reflector
  • Pick E3FA-TP21 for very-dark or very-shiny targets where retro-reflective is unreliable — pick for through-beam detection

Technical Specifications

Model E3FA-RP21
Series E3FA M18 Cylindrical Photoelectric Sensor
Type M18 retro-reflective with MSR, ABS plastic body, PNP, M12 connector
Sensing Method Retro-reflective with polarized MSR filter
Sensing Distance 4 m with E39-R1S reflector (sold separately); 6 m with E39-R2 large reflector
Min. Sensing Distance 100 mm
Standard Sensing Object Opaque, 80 mm dia min
Light Source Red LED, 624 nm, polarized
Output Type PNP open-collector, Dark-ON / Light-ON selectable
Switching Capacity 100 mA at 30 VDC
Residual Voltage 2 V max at 100 mA load
Supply Voltage 10 to 30 VDC, ripple 10 % p-p max
Current Consumption 25 mA max
Operating Temperature -25 to +55 °C (no icing)
Storage Temperature -30 to +70 °C

FAQ for E3FA-RP21

What is MSR (mirror surface rejection) on the E3FA-RP21?
MSR (mirror surface rejection) is a polarization-filter technique that allows the sensor to detect only real beam interruptions, not reflections from shiny surfaces. The sensor emits red light polarized at 90° (vertical). When this light hits the corner-cube retroreflector (E39-R1S), the corner-cube rotates the polarization 180° back to vertical, so it passes through the receiver's vertical-polarization filter.
What reflector do I need for the E3FA-RP21?
The E3FA-RP21 works with the E39-R1S corner-cube retroreflector (40 × 60 mm) for 4 m range, or the larger E39-R2 (80 × 80 mm) for 6 m range. The E39-R1S is the standard pick; the E39-R2 is for installations with longer distances. For smaller-distance installations where space is tight, the E39-R3 (15 × 30 mm small) reduces range to ~1 m. Order the reflector separately — it's not included with the sensor.
Can the E3FA-RP21 detect a clear-glass bottle?
Yes — the E3FA-RP21 detects clear-glass bottles (and clear PET, clear water bottles) because the beam must physically pass through the glass to reach the reflector, and the bottle blocks enough of the beam to trigger the sensor. Clear PET reduces beam transmission by ~20 %; clear glass by ~10 %; both are reliably detected at the 4 m E39-R1S range.
What's the difference between E3FA-RP21 and E3FA-RP11 2M?
E3FA-RP21 (this SKU) uses an M12 4-pin connector — the cable is removable and replaceable; the sensor body has an M12 connector port. E3FA-RP11 2M uses a pre-wired 2 m PVC cable — the cable is integral to the sensor body and cannot be replaced without replacing the sensor. Both have identical electrical specs (4 m range with E39-R1S, PNP, MSR polarized, IP67/IP69K).

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