Machine vision camera interface comparison: USB to CoaXPress

The interface is the one camera decision you cannot quickly undo. A lens swaps in ten minutes; moving from USB3 to CoaXPress means new cabling, a new host card, a different power scheme and a retest. This comparison puts numbers on the choice: payload rate per interface, the cable reach you can plan around, what each one demands at the host, and where the power comes from. A worked example runs one 12 MP camera through every option, and each case ends with a decision.

Pick the payload first, then the reach

Size the link in two steps: compute the image payload the camera must stream, then take the interface whose usable payload and reach both clear it with the least extra hardware.

The line rates are set by the standards. USB3 moves 5 Gb/s, GigE 1 Gb/s, 10GigE 10 Gb/s, CoaXPress up to 12.5 Gb/s per coax line, and Camera Link 2.04 Gb/s in base configuration or 6.8 Gb/s in full. Usable payload sits below the headline rate: USB3 pays about 20 percent for 8b/10b line encoding before packet overhead, so plan on roughly 3.5-4 Gb/s of image data. GigE with jumbo frames delivers close to its full 1 Gb/s; call it 110-118 MB/s.

Then decide reach. A camera on the bench within 3 m of the host makes USB3 the whole answer. Past that, run length, camera count and payload per camera drive the choice, and the sections below take them one at a time.

The interfaces at a glance

All five link families attach to the same area scan cameras; the sensor behind the link does not change what the link can carry.

Device counts follow the same pattern. A USB host controller addresses up to 127 devices, but everything hanging off one controller shares its 5 Gb/s. Ethernet scales through standard switches and multi-port NICs, and each port renews the bandwidth budget; the coordination cost moves into switch and IP setup instead. A Camera Link capture channel serves one camera by design, because the cable carries dedicated video lines rather than a shared packet stream.

Connectors follow the host world: USB Micro-B or USB-C on USB3, RJ45 on Cat 5e or Cat 6 for GigE, 26-pin SDR plugs on Camera Link, and standard 75 Ω coax connectors on CoaXPress.

Worked example: a 12 MP camera streaming 30 fps

The example camera is the 12 MP USB3 area scan camera LS-CMR-0166: 4000 × 3000 resolution, 30 fps, 1/1.7" sensor. Those printed values and one assumption - 8 bits per pixel, the usual mono 8 output - are all the arithmetic needs.

Bits per frame: 4000 × 3000 px × 8 bit = 96,000,000 bit, i.e. 96 Mbit (12 MB).

Stream rate at full speed: 96 Mbit × 30 fps = 2,880 Mbit/s, about 2.9 Gb/s or 360 MB/s.

Decision: USB3 carries this camera at full speed as long as the run stays inside its reach. If the camera must move further out, do not step down to GigE and keep 30 fps - the arithmetic forbids it. Take 10GigE, take CoaXPress, or accept about 10 fps.

Sensitivity: switch the pixel format to 12-bit and the payload grows by half - 144 Mbit per frame, 4.32 Gb/s at 30 fps. USB3 no longer fits, GigE caps near 7 fps (1,000 ÷ 144 = 6.9), and one CXP-6 line at 6.25 Gb/s still carries it with roughly a 30 percent margin. The pixel format is as decisive as the resolution.

USB3: the short-cable workhorse

USB3 needs no capture card, powers many cameras straight over the cable, and plugs into any modern PC. That is why it dominates bench work, single-camera prototypes and compact machines. The practical limit is reach: about 3 m of passive copper is the dependable figure, and a marginal or over-length cable shows up as a frame rate that collapses mid-run rather than as a clean disconnect. That failure has its own USB frame rate troubleshooting guide, and the same cable physics bounds USB runs on 3D cameras.

Bandwidth scales per controller port. Each root port carries its own 5 Gb/s, while a hub divides one port's budget among everything below it. Two cameras on two ports stream two full-rate payloads; the same two cameras behind one hub share one budget.

The catalog carries the same 6 MP camera family on both links: a USB3 twin and a GigE twin. With USB3's usable image payload roughly three to four times GigE's, the USB3 twin moves that much more data when the sensor runs flat out.

High-resolution fast work fits the link too: MV-CH120-11UC pairs a 12 MP global-shutter sensor in the 1.1" format with USB3.

For choosing between sensors on this interface, the USB3 camera selection guide covers the sensor side of the decision.

GigE and 10GigE: reach first, rate second

GigE runs 100 m per segment on ordinary Cat 5e or Cat 6 through standard switches, and the camera side needs no extra hardware beyond a NIC. The tax is bandwidth: about 110-118 MB/s of image payload per port. To see where that bites, take MV-CS200-10GC, a 20 MP GigE camera. At 8 bits one frame is 20 Mpx × 8 bit = 160 Mbit, so the port tops out near six full-resolution frames per second (1,000 ÷ 160 ≈ 6.3). At reduced resolution or slower streams it is entirely comfortable - GigE punishes only payloads that are big and fast at once.

Multi-camera systems live on switches, and a shared hop spends the same budget twice. Divide bandwidth per port before choosing topology - the multi-camera GigE bandwidth budget guide works through that split - and fit a high-performance NIC driver on the host before blaming the cable. The GigE Vision frame rate guide runs the same per-link arithmetic for a single fast camera.

10GigE keeps the Ethernet model - long Cat 6a or Cat 7 runs, fiber where the copper stops, standard switches - and multiplies the rate by ten. The host side is the part people under-order: a 10GbE port wants a real PCIe NIC with lanes to feed it. The MV-GT2104 puts four copper 10GigE ports on one card. Machine vision cameras rarely take PoE at 10GigE, so order the camera's power lead either way.

CoaXPress: rate per line, length traded for speed

Each CoaXPress coax line carries up to 12.5 Gb/s, and cameras can combine lines for more. Reach falls as rate rises: the standard's planning figures give more than 100 m per line at 3.125 Gb/s, on the order of tens of metres at 6.25 Gb/s, and roughly 15-30 m at 12.5 Gb/s with a good cable. At order time, the coax maker's length table for your line rate is the deciding document.

Two properties make CXP the default for big, fast sensors. Power rides in the coax - up to 13 W at nominal 24 V - so one cable does data and power. And the link terminates in a card at the host, giving deterministic capture without USB-style bus arbitration.

Budget the card on day one: a CXP-6 frame grabber such as MV-GX1008 terminates the camera run and belongs in the parts list beside the coax, not as an afterthought.

Camera Link: the 10-metre lane

Camera Link predates all of this and still runs hard: 2.04 Gb/s of dedicated video in base configuration, 6.8 Gb/s in full, over a 26-pin cable limited to about 10 m. A capture card is required, power arrives separately, and one capture channel serves one camera. A 5 m SDR-to-SDR Camera Link cable LS-CBL-0191 is the standard run between camera and card.

For a station that keeps existing cards, the Camera Link frame grabber compatibility guide covers the pairing checks. For new designs, CoaXPress reaches higher per-line rates with power in the cable and 10GigE covers similar throughput on network hardware, so Camera Link earns its place mainly through installed fleets, spare-part stocks and the odd line scan camera that ships only in this format.

Power and cabling you actually buy

Most GigE installs take one of three power paths: a PoE port at the host, a PoE injector in the cable run, or a locking 6-pin or 12-pin power-and-I/O cable from its own supply. PoE needs support at both ends - camera and port. Where a camera has no PoE, that power-and-I/O cable is the only way in, and it also carries the trigger and I/O lines, which is why the camera cables category separates data from power. On the host side, MV-GE2002P is a dual-port PoE NIC.

USB cameras usually draw power over the bus; many industrial models also expose an auxiliary input for hosts whose ports cannot be trusted to deliver. The trade-offs live in the camera power guide. CoaXPress goes the other way and ships up to 13 W down the coax at nominal 24 V, removing a power supply from the cell.

Which interface for which case

• Bench or prototype, camera within 3 m of the host: USB3. Usable payload up to roughly 4 Gb/s, no card, no driver work.
• Camera mounted 10-100 m out, stream well under 1 Gb/s, possibly several cameras: GigE on standard switches.
• Stream between 1 and 8 Gb/s over a long run: 10GigE on Cat 6a or fiber, with a real PCIe NIC.
• Big sensor, high frame rate, deterministic capture, coax run: CoaXPress, sized line-rate first and cable length second.
• Existing Camera Link cards or a Camera Link-only camera: Camera Link for that station, and nothing new beyond it.

The worked example above is the pattern to copy: one payload number against one usable-rate number decides the interface, and reach eliminates whatever fails the run length.

Checks before ordering

• Payload arithmetic first: width × height × bytes per pixel × fps against the usable rate, using the pixel format you will actually run.
• Walk the real cable route, including dress, vertical drops and service loops - USB lives and dies by the 3 m figure.
• Host check: a free PCIe slot of the right generation for 10GigE NICs and capture cards. Laptops throttle every one of these links, as the laptop frame grabber guide details; a desktop-class machine such as the industrial mini PCs range takes the card properly.
• Power: PoE confirmed at both ends, or the power-and-I/O cable ordered with the camera.
• Trigger wiring: confirm the power-and-I/O connector's pin count - 6-pin and 12-pin are the common ones - before ordering cables.
• CXP and Camera Link: order card, cable and camera as one set, with the cable length table checked against the line rate.

When the usual answer is wrong

• "GigE's 100 m makes it the default." Reach is not bandwidth. The worked example's 12 MP camera manages about 10 fps over GigE at full resolution; if the inspection needs 30 fps, the 100 m is worthless.
• "USB3 is lab-grade only." A 12 MP stream at 30 fps fits inside USB3 with headroom. The constraint is cable length, not capability.
• "CoaXPress means long cable automatically." Reach falls hard as line rate rises; at 12.5 Gb/s you may be under 30 m, shorter than a Cat 6a Ethernet run.
• "Any PC with the right port works." A throttled NIC driver or a shared USB controller halves the budget before the camera is even connected.

Where to start

Put your width, height, bytes per pixel and frame rate into the payload formula, match the result against the table above, and let reach eliminate the rest. The camera finder filters area scan cameras by interface, the frame grabbers category covers the card side, and the camera configurator walks the whole chain in order. If a link rate comes out marginal, send the numbers through the contact page before ordering - the host-side and acquisition guides on the systems topic page cover the next layer of detail.