Area scan cameras

How to choose an area scan camera

An area scan camera takes a full two-dimensional image with each exposure. It is the default camera for inspection, gauging, PC-based code reading and robot guidance whenever the part can be imaged in one shot. The choice comes down to six things: pixels, shutter, mono or colour, interface, sensor format with the lens mount, and the environment it has to survive.

1. Resolution: pixels on the smallest feature

Start from the field of view and the smallest detail you must see. Divide the field of view by the feature size and allow at least 3-4 pixels across the feature for detection, more for repeatable measurement. A 100 mm field with 0.1 mm defects needs about 3,000-4,000 pixels across, which points to a 12 MP class sensor rather than a 5 MP one. The camera resolution calculator does this for your numbers.

2. Shutter: global for moving parts

A global shutter exposes every pixel at the same moment, so a part on a conveyor is not skewed. A rolling shutter reads the sensor row by row; it is fine for stationary parts and slow scenes, and it is often the cheaper way to get very high pixel counts. For motion, also keep the exposure short enough that the part moves less than about one pixel during it - the motion blur calculator gives the limit, and a strobed light usually supplies the light that a short exposure needs.

3. Mono or colour

Mono sensors are more sensitive and resolve finer detail per pixel, because a colour sensor splits its pixels between red, green and blue behind a Bayer filter and interpolates. Use mono for measurement, edges, code reading and low light; use colour only when the decision depends on hue. A mono camera with a coloured light often separates colours well enough.

4. Interface: bandwidth, cable length, PC side

Data rate = width x height x frames per second x bytes per pixel. Compare it with what the link carries in practice:

Leave 20-30 % headroom. Several GigE cameras on one switch share its uplink, so give each camera its own port when they run at full speed. The camera bandwidth calculator checks a camera against a link, and the industrial PC guide covers the PC side.

5. Sensor format and lens mount

The sensor format sets which lenses fit: the lens image circle must cover the sensor diagonal or the corners go dark. Formats up to 1.1 inch use C-mount lenses; larger sensors use M42, M58, M72 or F-mount. Pick the camera first, then a machine vision lens rated for that format and for the pixel size - small pixels (2.4 µm and below) need lenses rated for high resolution.

6. Environment and wiring

Check the working temperature, the IP rating, the supply (9-24 V DC or PoE on most models here, bus power on USB models) and the I/O: one opto-isolated trigger input and one output is common; some models add more lines.

What this range covers

• Resolution: from 0.3 MP (640 x 480) up to large-format sensors of about 150, 245 and 604 MP; most stations use 1.3-25 MP.
• Sensor formats: 1/4 inch to 1.1 inch, plus APS-C, APS-H, medium and large format. The most used formats have their own pages, such as 2/3-inch area scan cameras.
• Interfaces: GigE, 2.5GigE, USB3, 10GigE, CoaXPress and Camera Link.
• Frame rates: from a few fps on the largest sensors to several hundred fps on small ones; high-speed models reach thousands of fps at reduced resolution.
• Spectrum: visible mono and colour, plus NIR, UV and SWIR (InGaAs, 900-1700 nm and 400-1700 nm) models.
• Housing: mostly IP30 / IP40; IP67 versions where washdown or dust is expected. Where stated, most models run from -30 to 50 °C (some to 60 °C), others from 0 to 50 °C.

Typical applications

• Dimensional gauging of machined and stamped parts, usually mono with a backlight or a telecentric lens.
• Surface and print inspection on labels, packaging and PCBs.
• Reading DataMatrix, QR and barcodes from a PC when a dedicated reader is not flexible enough.
• Robot guidance and pick-and-place from a fixed or arm-mounted camera.
• Moisture, fill-level and sorting checks with SWIR models, where water and many plastics look different than in visible light.

Common mistakes

• Choosing by megapixels alone: an oversized sensor slows the frame rate and the inspection.
• A rolling shutter on a moving conveyor.
• Putting a 12 MP camera behind a lens rated for 2 MP or for a smaller format.
• Forgetting the trigger: free-running cameras give images that do not line up with the part.
• Colour where mono with the right light colour would give more contrast.

Questions

GigE or USB3?
GigE allows long cables, PoE and easy multi-camera networks at about 115 MB/s per camera. USB3 gives more bandwidth per camera but needs short cables and a good USB controller per camera.

When do I need 10GigE or CoaXPress?
When the data rate goes beyond about 300 MB/s: high resolution at high frame rates, for example 25 MP at 30 fps or more. 10GigE stays on standard network hardware; CoaXPress needs a frame grabber but gives the highest rates and deterministic triggering.

Does the camera include a lens?
Almost never: apart from a few models with integrated optics, area scan cameras come without a lens, so pick one that covers the sensor format and matches the mount. To check a full set at once, configure a vision system starting from the camera.

Area scan or line scan?
Area scan for discrete parts that fit in one image. Use line scan cameras for continuous webs, very long parts and cylinders that rotate in front of the camera.