You have a camera with a USB plug and a PLC HMI that should show its video live. That pairing does not work: PLC panels that support camera video take it over Ethernet — the documentation lists TCP, UDP and RTSP — and USB camera connection is not supported. This explainer is for integrators and controls engineers adding a machine view to an operator panel. You will see why USB cannot reach the screen, what the panel's video widget can actually play, which camera types deliver that stream, and the bandwidth, pixel and cable numbers that make the first installation the stable one.
The decision: one Ethernet camera, one cable
Put the camera on the panel's Ethernet switch, not on its USB port, and make it a camera that serves video itself. That means either a smart camera whose live view is an MJPEG or RTSP stream, or an industrial camera with a small PC beside it that republishes the feed as a stream. That is the whole decision; the numbers behind it follow.
For a monitoring view, choose the smart camera. It streams on its own, so the panel opens a URL and the video appears, with no extra hardware in the cabinet. Choose the industrial camera plus restream PC when the same image must feed inspection software, because a vision job and the operator view then share one sensor. A USB camera is off the list, and no adapter changes that.
Why USB cannot reach the panel
USB is a host-peripheral bus. The camera is a peripheral, and something must act as its host: enumerate the device, load a driver for it (normally the USB video class), and turn packets into frames. A PLC HMI's firmware is a fixed set of functions — tag display, alarms, trends and a short list of widgets. There is no USB video driver in that firmware and no mechanism to add one, so a USB camera plugged into the panel's port is simply not a device the panel knows. That port exists for a mouse, a keyboard or a memory stick.
Distance rules the idea out even where a driver exists. A passive USB 2.0 segment reaches about 5 m and USB 3.x about 3 m; machine cameras usually sit farther from the panel than that, and active extension repeaters are one more failure point on a production line. One Ethernet segment covers 100 m on Cat5e or Cat6. For how the interfaces compare across a whole vision system, read the most reliable camera interface: GigE, USB3, Camera Link or CoaXPress.
What the panel's video widget plays
Panels that accept camera video expose a video or IP-stream widget: you configure a URL, and the widget renders the stream on the screen. Two protocols cover nearly every PLC HMI on the market. MJPEG sends complete JPEG frames over HTTP, conventionally on TCP port 80. RTSP is a session protocol on TCP port 554 that usually carries H.264 or H.265 video. Where the panel has a hardware video decoder, the widget offloads to it and the panel's CPU keeps its headroom. Set-up walk-throughs for both protocols are in display an MJPEG stream in an HMI screen and display an RTSP camera stream in an HMI: snapshot URL or VLC.
Start with MJPEG. Every frame is independent, decoding is light on the panel, and latency is low. The price is bandwidth: MJPEG is several times heavier than H.264 for the same view. Move to RTSP with H.264 when you run many cameras, share a slow link, or know the panel decodes H.264 in hardware. When motion is not needed at all, a snapshot URL polled on a timer is lighter still — live camera image on an HMI panel: streaming vs snapshot limits draws the line.
Camera choice: streamer or industrial camera
Path A — a smart camera. A smart camera packs sensor, light and processor in one housing, runs its inspection job on board, and puts a live view on its Ethernet port. Point the panel's widget at that view: one cable, one address, no PC. What the panel can display from a smart camera, and what stays device-side, is set out in smart camera image in a PLC HMI: what actually displays live; dashboards that mix video with numeric readouts are covered in stream smart camera live video and metrics to a custom dashboard.
A first pick for a monitoring view:
- Interface
- GigE
- Resolution
- Up to 3 MP
If the view needs more detail, a 6 MP model such as the MV-SC5060XM-08M-WBN with its 8 mm focal-length lens and M12 mount covers a wider scene from closer in.
Path B — an industrial camera plus a restream box. Vision cameras speak GigE Vision, an acquisition protocol for vision software, not a media stream a widget can open. The standard pattern is a small industrial PC running the vision software and publishing the processed image as MJPEG or RTSP; the panel plays that. Use this path when inspection and display share one sensor, because what the operator watches is then exactly what the software measures.
On this path a compact area scan camera keeps the lens choice open:
- Sensor format
- 1/1.7"
- Lens mount
- C-mount
- Interface
- GigE
- Resolution
- Up to 3 MP
The restream box belongs at the machine, and industrial mini PCs are built for exactly that fanless, bracket-mounted role.
| Path | The panel plays | Best when | Extra hardware |
|---|---|---|---|
| Smart camera, MJPEG | MJPEG over HTTP | One view, one cable | None |
| Smart camera, RTSP (H.264) | RTSP stream | Several cameras, slow link | None |
| Industrial camera plus PC | MJPEG or RTSP from the PC | Inspection and display share a sensor | Industrial PC |
The bandwidth arithmetic
Bitrate decides how many cameras the link carries, and it follows from three settings you control at the camera: frame size, frame rate and codec.
Worked example, MJPEG. A 1920 × 1080 JPEG frame at mid quality runs about 60–150 kB; take 100 kB as typical. At 10 fps: 100 kB × 8 = 800 kbit per frame; 800 kbit × 10 fps = 8,000 kbit/s = 8 Mbit/s. HTTP and TCP overhead adds roughly 15%, so plan 9.2 Mbit/s per stream.
Link budget. Keep camera traffic under half the link speed so PLC I/O and programming sessions are untouched. On a 100 Mbit/s port that is a 50 Mbit/s budget: four streams at 9.2 Mbit/s come to 36.8 Mbit/s, which fits with headroom. On GigE the wire stops being the constraint at dozens of streams, and the panel's decoder becomes the ceiling. Four 1080p MJPEG streams is the design point for a Fast Ethernet link; two is the comfortable number for a mid-range panel decoding in software.
For the same 1080p view, H.264 typically lands at 2–4 Mbit/s — one quarter to one half of MJPEG — at the cost of codec support in the panel and slightly higher latency.
Arranging several cameras on one screen has widget and refresh behavior of its own; display multiple IP camera streams on one HMI screen works through it.
Match the stream to the panel's pixels
Every pixel the camera sends that the panel cannot show is bandwidth paid for nothing. Common PLC panel sizes: 800 × 480 = 384,000 px (0.4 MP), 1024 × 600 = 614,400 px (0.6 MP), 1280 × 800 = 1,024,000 px (1.0 MP) and 1920 × 1080 = 2,073,600 px (2.1 MP).
Send a full 1080p stream to a 1024 × 600 panel and it displays 614,400 of 2,073,600 pixels — 30% of them. The other 70% of the bitrate is thrown away at the screen. When the camera or the restream box can scale its output, set the stream to the panel's native size and leave full resolution to the inspection job. Aspect ratio matters too: most vision sensors are 4:3 while many panels are 16:9, so the picture letterboxes — 16, 20 or 24 MP camera: pick by aspect ratio and format lays out the formats.
To size a sensor against the panel view and any measurement task together, start here:
Network plan: one subnet, fixed addresses
Put the panel and the camera on one subnet and one switch — for example panel 192.168.1.10, camera 192.168.1.20, mask 255.255.255.0, both static. RTSP opens its session on TCP 554, but the media itself often rides UDP ports that routers between subnets drop; keeping camera and panel on the same switch removes that whole class of failure. The address plan is worked through in camera static IP setup: reach a smart camera on the same subnet.
Cable the run
One Ethernet segment spans 100 m on Cat5e or Cat6 — usually the whole machine and then some. Choose the cable by the motion it lives in: a fixed run takes a standard data cable, a camera riding a gantry needs a drag-chain rated high-flex cable, and vibration zones want locking or screw-down connectors that cannot walk out. Camera cables are grouped by exactly these jobs.
Cable styles for the two kinds of run:
- Type
- Camera data cables
- Length
- 15 m
Match the length to the route with a service loop; the cable pulled taut at its connector is the one that fails first.
When the Ethernet answer is wrong
The panel is a PC, not a PLC HMI. Panels running Windows or Linux can host a USB camera driver themselves. On Linux, whether the camera appears at all as a video device comes down to V4L2 driver support — USB camera live stream in an HMI: V4L2 driver support decides gives the checks. If USB cameras are mandatory at that machine, an industrial panel PC is the host that runs them.
You reach for a surveillance IP camera. It serves RTSP out of the box, but it has no strobe, no trigger input and no PLC-facing I/O. Fine for watching a doorway; wrong the moment the image feeds a decision.
You consider a wireless bridge. It removes one cable and adds jitter, dropouts and a security surface. Route the Cat6 instead — 100 m is a long way.
Before you order: the checklist
- Open the panel's video widget in its editor and read the protocol list it offers — MJPEG, RTSP or both — plus any codec limit and the number of stream widgets it allows.
- Multiply cameras by 9.2 Mbit/s (1080p MJPEG at 10 fps) and keep the total under half the link speed.
- Set each stream to its panel's native pixels; keep full sensor resolution for inspection.
- Reserve two static addresses on the panel's subnet — one for the camera, one spare.
- Pick the cable class for the motion: fixed, drag-chain, locking connectors.
- If one camera serves inspection and display, confirm the smart camera streams while its job runs.
Ready to pick parts? The camera finder filters by interface and resolution, and the system configurator walks camera, lens, light and controller in one pass. For multi-camera layouts across several panels, contact us and we will size the link with you.
问题
Can a USB-to-Ethernet adapter make a USB camera work on the panel?
No. The adapter moves USB packets down a wire; the panel would still need a USB host driver for the camera, and its firmware ships none and accepts none. The widget wants a URL it can play. The only working equivalent is a small PC that hosts the camera and republishes it as MJPEG, which is more hardware than buying an Ethernet camera in the first place.
Will a GigE Vision camera show up in the panel's video widget?
No. GigE Vision is an acquisition protocol for vision software on a PC; a video widget cannot open it. Either run vision software on an industrial PC and point the widget at the MJPEG or RTSP stream that software publishes, or choose a smart camera, which serves its live view over Ethernet by itself. The widget protocols are RTSP and MJPEG; GigE Vision is not on that list.
How many camera streams can one panel display?
Budget by bandwidth first. One 1080p MJPEG stream at 10 fps costs about 9.2 Mbit/s with overhead, so a 100 Mbit/s switch port carries four with room left for PLC traffic; a GigE port is not the constraint. The panel's own decoder sets the real ceiling. Dropping a stream to 1280 × 720 cuts the pixel count to 921,600, 44% of 1080p, and roughly halves that camera's bitrate.
What frame rate does an operator view actually need?
Five to ten frames per second reads as live video for machine monitoring; 15 fps only earns its bandwidth when the scene moves fast, and inspection never runs on the panel anyway. Bitrate scales linearly with frame rate, so dropping from 10 fps to 5 fps halves the stream with no visible loss on a static machine view. Set the frame rate at the camera and spend the savings on more views.
What URL goes into the panel's video widget?
For MJPEG it is an HTTP address, for example http://192.168.1.20/stream, where 192.168.1.20 is the camera's static address and the path names its stream. For RTSP it looks like rtsp://192.168.1.20:554/stream1, port 554 being the RTSP default, usually omitted. The exact path is printed in each camera model's documentation; type it once and the widget keeps it.