Allen Bradley42SMP-7321-QDFixed-Focus Diffuse Photoelectric Sensor, Mini Rectangular, PNP NO/NC, 11-28 V DC, Green 570 nm LED, Quick Disconnect

Product Description

What this part is

An Allen-Bradley 42SMP-7321-QD photoelectric sensor from the Rockwell Automation PHOTOSWITCH Series 7000 range. It is a fixed-focus diffuse sensor in a mini rectangular housing: emitter and receiver sit in the same body, and the sensor detects a target by the light it reflects back. Output is a PNP transistor with selectable normally open or normally closed action, and the sensor terminates in a quick-disconnect connector.

Decoding the designation

Within the 42SMP number the SMP prefix identifies the mini rectangular Series 7000 housing style, and the four digits that follow specify the sensing mode, output type and light source. The trailing QD marks the quick-disconnect version, which terminates in a connector rather than a fixed cable. That suffix matters because the QD and cable versions of the same sensor are not the same article to install.

What these specs mean in practice

A fixed-focus diffuse sensor differs from a standard diffuse sensor in a way that decides most applications. A standard diffuse sensor responds to anything reflective within its range, so a background wall or conveyor bed can trigger it. A fixed-focus sensor has its optics set to a defined focal distance, and it responds only to targets at that distance. Objects nearer or further away fall outside the focus and go undetected, which gives reliable detection of a small target close to the sensor without the background interfering.

That behaviour makes fixed focus the standard choice for registration mark detection, small part presence at a fixed position, and label and web edge sensing, where the target sits at a repeatable distance and background suppression matters more than range.

A PNP output sources current to the load, which suits the sinking input cards common on North American PLCs, and selectable normally open or normally closed action means the same sensor covers both a presence signal and an absence signal without changing hardware.

Published specifications

Function: photoelectric sensor, fixed-focus diffuse
Product line: Allen-Bradley PHOTOSWITCH, Series 7000
Housing style: mini rectangular
Field of view: 0.60 in
Minimum sensing distance: 0.2 in
Supply voltage: 11–28 V DC
Switching output: PNP
Output action: selectable normally open or normally closed
Light source: green LED, 570 nm
Termination: quick-disconnect connector (QD)
Catalogue number: 42SMP-7321-QD

Quantity and configuration

Sold as 1 Pc — one sensor. The mating quick-disconnect cordset is not included, and no mounting bracket is included.

Installation and setup notes

The sensor mounts so that the target passes through the focal zone, and detection is set by positioning rather than by adjusting range, which is the practical consequence of fixed-focus optics. A quick-disconnect cordset of matching connector style completes the wiring. The green 570 nm light source gives good contrast on many printed registration marks, which is one reason this light colour is specified in place of infrared.

Interchange guidance

The 42SMP-7321 without the QD suffix is the same sensor supplied with an integral 3 m cable instead of a connector, so it is the same sensing function in a different termination and is a related article rather than a drop-in for a connectorised installation. The 42SMP-7320-QD, 42SMP-7021-QD and 42SMP-7000-QD are further Series 7000 mini rectangular sensors in the same housing with different sensing modes, output types or light sources; a differing sensing mode makes them different parts. A direct replacement matches catalogue number 42SMP-7321-QD.