How to control the bandwidth use of an industrial USB3 camera by limiting its framerate

Bandwidth is the amount of data which can be transmitted over a certain interface (USB3 / GigE / 5GigE) during a certain period. The higher the bandwidth of the interface, the more and faster data can be received or sent. This article will explain multiple options for bandwidth control and how to calculate the required framerate for your industrial USB3 camera.

To control the bandwidth of industrial USB3 cameras, we need to understand how the USB3 connection works and how to determine which framerate values we need.

USB3 INDUSTRIAL VISION CAMERA ADVANTAGES

USB3 is a suitable interface for high resolution and high-speed cameras. The USB3 connection has a maximum bandwidth of 480 megabytes per second. This is 10 times faster than USB2 and 4 times faster than GigE. Every computer and almost all developer boards come with USB3 ports. The USB 3.0 camera uses less processing power than a USB2 camera. Take note that the software and cameras need to reserve parts of this 480Mbps for packet retransmission, so the usable bandwidth is 400 Megabytes per second.

USB3 CHIPSET, BUS AND PORTS

You may have multiple USB3 ports on your computer, or host device. Those are usually shared via one BUS to one chipset. The total speed will be shared between these ports. For instance, with our Adapter PCIe1x you benefit from 4x USB3 speed ports, with shared bandwidth between them.

On systems with more chipsets, or a PCI cards such as Adapter PCIe4x you have 4x USB3-ports, and each port has its own chipset. This results in 4 full speed connections.

WHY LIMIT THE BANDWIDTH OF AN INDUSTRIAL USB3 CAMERA

When connecting multiple industrial cameras to one computer via USB3 connector, we have to limit the bandwidth of every camera, so that each device uses a specific amount of bandwidth. This will make sure images are transferred in a stable way from the camera to the PC, with constant and stable framerate. Incorrect parameters will cause incomplete images, or no images at all.

CALCULATE THE INDUSTRIAL CAMERA USB3 FRAME RATE

To calculate the frame rate we need to use the INDUSTRIAL CAMERA USB3 FRAME RATE calculator. Previously, after installing the Galaxy SDK, you would find this calculator in the following folder: C:\Program Files\Daheng Imaging\GalaxySDK\Doc\

Since the latest SDK update the frame rate calculator is no longer included. Dowload it seperatly from our download area.



In our example we will connect 3 MER-502-79 FPS USB3 industrial vision cameras to one USB3 controller with 3 USB3 ports. This camera has a framerate of 79FPS.



This is showing the standard framerate results of 79.19 FPS using the default bandwidth value 400Mbps, or 400000000 bps.

Considering the maximum Throughput limit of 400Mbps, each camera will be set to use 1/3 of this data amount. 400Mbps/3 Cameras = 133.3 Mbps per each camera.

This is showing the new framerate results of 26.53 FPS using 1/3 bandwidth value 133.3 Mbps, or 133000000 bps

HOW TO MODIFY THE INDUSTRIAL CAMERA USB3 BANDWIDTH IN THE GALAXY VIEW SOFTWARE

To modify the INDUSTRIAL CAMERA USB3 BANDWIDTH in the galaxy software, please connect to each camera and navigate to the menu: Remote device / Device control / DeviceLinkCurrentThroughputLimit

Here you can modify the standard 400000000 bps to the value of your calculation. In our case, this is 133000000 bps. Now images are transferred in a stable way from the camera to the PC.