Banner Q20-2PLP-2M Polarized Retroreflective Sensor

Compact polarized retroreflective sensing to 5 m with a PNP output

The Q20-2PLP-2M is a compact plastic-housing polarized retroreflective photoelectric sensor from Banner Engineering’s Q20-2 range. Its visible red 645 nm LED, together with a polarizing filter, lets it see shiny or reflective objects reliably across distances up to 5000 mm when used with a BRT 92x92C reflector. Threaded brass inserts on the housing provide stable mounting points even in tight machine spaces.

Setup is deliberately simple: a single-turn gain potentiometer trims sensitivity, and a light-operate / dark-operate switch selects the output logic. Bright green and amber indicators on top show power and signal state, and the amber LED flashes when the sensing condition is marginal.

Technical specifications

Choosing among the Q20-2 retroreflective models

The datasheet covers four retroreflective part numbers that differ only in output electronics. Q20-2PLP-2M is the PNP three-wire sensor with a LO/DO switch, Q20-2NLP-2M the NPN equivalent, and Q20-2VPLP-2M and Q20-2VNLP-2M are four-wire complementary versions with one light-operate and one dark-operate output. Pick the PNP three-wire version when the PLC input card expects sourcing signals and only one output is needed.

Because the range figure is given against the large BRT 92x92C reflector, shorter distances will be achieved with smaller reflectors; the sensing range should be confirmed against the actual reflector and contamination level at the installation.

Mounting, wiring and ordering

Brackets, if used, are fitted to the brass inserts before the sensor is bolted on, and the manufacturer asks that overcurrent protection be supplied by the end application according to its table, using either external fusing or a Class 2 power supply. Supply leads smaller than 24 AWG should not be spliced.

To order a pigtail connector version, replace the 2M suffix with Q3 for a 150 mm cable and 3-pin M8, Q for 4-pin M8 on three-wire models, or Q5 for a 4-pin M12. Quick-disconnect models need a mating cordset ordered separately.

Aligning the sensor and reflector

A retroreflective sensor works only as well as its alignment. Mount the Q20-2PLP-2M and its reflector on rigid brackets so that machine vibration cannot shift the beam, and position them so the target passes completely through the beam rather than clipping its edge. With the gain potentiometer at a moderate setting, move the sensor slowly in both directions to find the edges of the region where the amber indicator shows light sensed, then fix it in the centre of that region. Afterwards, check that the amber LED does not flash, since flashing indicates marginal sensing that may fail as the lens or reflector becomes dirty.

Set the gain high enough for reliable detection at the installed distance but not so high that the sensor ignores semi-transparent objects. Pass a real product through the beam several times and confirm the output changes cleanly every time.

Detecting shiny objects

The polarizing filter is the main reason to choose this sensor for packaging and handling lines with shrink-wrapped, metallic or glossy items. It helps the sensor tell the difference between light returned by the corner-cube reflector and light reflected directly by a shiny surface. Even so, use a reflector type suited to polarized sensors, and avoid angling a highly reflective target face directly back toward the sensor. If false triggering still occurs, tilting the sensor slightly relative to the target path often solves it.

Wiring to the PLC

Connect the three wires of the cable to the supply and to a sourcing-compatible PLC input, following the colour code in the Banner datasheet. Select light operate or dark operate with the switch according to whether the PLC logic expects the output on when the beam is clear or when it is blocked. Keep the total load within the output rating listed above, and route the sensor cable away from motor and power cables to avoid interference.

Maintenance on dusty Omani sites

In Oman, dust from cement, food, fertiliser and general warehouse operations settles quickly on lenses and reflectors and reduces the returned signal. Include a gentle lens and reflector clean in routine maintenance, using a soft cloth and a cleaner compatible with the acrylic lens cover, and recheck that the amber indicator is steady afterwards. Where sensors sit near doors or loading bays, shield them from direct sunlight entering the sensor lens, and secure the cable so it cannot be damaged by forklifts or cleaning crews. Recording the final gain setting for each sensor position makes it easier to restore correct operation after a bracket has been knocked or replaced.

Documents and quotation

Use the request form to ask for this model with your exact code. The attached Banner Q20-2 Polarized Retroreflective Sensors with Visible Red LED datasheet, p/n 227993 (manufacturer, unaltered) lists all variants and options, and the output type, reflector and cable suffix should be confirmed before the order is released. Other products of this kind can be found in Sensors & Transmitters.