Fixed code readers

How to choose a fixed code reader

A fixed code reader is a small camera with built-in lighting, optics and decoding that reads 1D barcodes and 2D codes on parts as they pass, then sends the result to a PLC or host. Unlike a handheld scanner it is mounted on the line and triggered automatically. The right reader follows from the code, the field of view, the distance and the speed of the line.

1. The code: symbology, size and marking

List every code the station must read. The readers here decode the common 1D codes (Code 39, Code 93, Code 128 / GS1-128, EAN, UPC, ITF, Codabar and, on many models, MSI, Code 11, Industrial 2 of 5 and Pharmacode), 2D codes (Data Matrix, QR, Micro QR, Aztec on most) and stacked PDF417; the full list is on each product page. Then note the smallest element size: the narrow bar width of a 1D code or the cell size of a 2D code, in mil (1 mil = 0.0254 mm). Where stated, the finest readable codes are down to 2 mil (1D) and 5 mil (2D) on high-resolution short-range models. Printed labels are the easy case; direct part marks (dot peen or laser-etched Data Matrix on metal) need more resolution and the right light. See Industrial 2 of 5 support in fixed readers for one symbology that is often missed.

2. Resolution and field of view

The field of view must cover the area where the code can appear, including position tolerance on the conveyor. Then check the pixels per element: as a rule of thumb, at least about 1.5-2 pixels per narrow bar for 1D codes and 3-5 pixels per cell for 2D codes, more for damaged or low-contrast marks. Field width divided by the horizontal pixel count gives the size of one pixel on the part. Sensors in this category run from 640 x 480 to 20 MP and more; most readers use 1.3-5 MP, and the larger sensors cover wide conveyors or several codes in one image.

3. Working distance and focus

Each reader's depth of field is stated per code size on its product page. Fixed-focus readers suit a constant distance. Manual-focus models with M12 or M10 lens mounts are set once at installation. Readers with a liquid lens (D14 mount) refocus electronically, which handles boxes of different heights. A few larger readers take C-mount lenses for long distances or very small fields.

4. Speed

Frame rates in this category run up to 92 fps and decode rates, where stated, up to 120 codes per second. On a moving line, also check the exposure: blur in the direction of motion must stay under about half an element. Global shutter sensors, used on most readers here, avoid the skew that rolling shutters produce on moving codes. For multi-sided tunnel reading, plan one reader per face.

5. Lighting and aiming

Built-in light is red by default on most models, with white, blue, infrared, UV or red/blue dual-colour versions available. Polarized lens caps cut glare on shiny labels, film and metal; diffuse caps help on curved and direct-marked parts. An aimer (green, red or orange LED pattern, or a cross laser on some models) makes setup easier. For hard direct part marks, an external ring light or dome light can replace the built-in one.

6. Interface and integration

Readers connect over Fast or Gigabit Ethernet, USB 2.0 or RS-232. Ethernet models typically speak TCP client and server, UDP, FTP for images and the common PLC protocols - PROFINET, EtherNet/IP, Modbus TCP and, on most, SLMP / MC protocol and FINS - so the result goes straight into the PLC without a gateway. USB readers can act as a keyboard (HID) or virtual serial port; see USB barcode data capture. Power is 24 V DC or 12-24 V DC on most Ethernet readers, 5 V from the USB port on small ones. Isolated inputs take the trigger from a photoelectric sensor; outputs signal good read / no read.

What this category covers

Typical applications

• Traceability: reading Data Matrix codes on PCBs, castings and machined parts at each station.
• Logistics and parcel sorting: 1D labels on cartons on a conveyor, often with a liquid-lens reader for varying box heights.
• Pharmaceutical and food packaging: GS1 Data Matrix and GS1-128 on cartons and labels.
• Battery cells, tyres and automotive parts with laser-etched or dot-peened codes.
• Verifying the code before a robot picks a part; see barcode verification before picking.

Common mistakes

• Choosing by maximum reading distance alone, then finding the code is too small for the pixels at that distance.
• Mounting the reader square to a glossy label. Tilt it 10-15° so the light's reflection does not hit the lens.
• Leaving the exposure long on a fast line: the code blurs and the read rate drops.
• No trigger. Free-running readers can report the same code twice or miss gaps between parts.
• Forgetting the IP rating depends on the lens cap being fitted correctly.

Questions

Code reader or smart camera?
A code reader is tuned for decoding and is simpler to set up. If the station also has to inspect, measure or check presence, a smart camera does both.

Can it read damaged or low-contrast codes?
Most readers handle partly damaged codes, and image preprocessing helps; see 1D barcode preprocessing for rotation, blur and glare. Better lighting usually helps more than a higher resolution.

What accessories do I need?
A power and I/O cable, a mounting bracket and, for some models, a different lens or lens cap: see code reader accessories and cables.