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MultiCam Boards Documentation > MultiCam Documentation > MultiCam User Guide > General Topics > Frame Grabber Topics > Line-Scan Frame Grabber Topics > Line Rate Modes

Line Rate Modes

The "line rate mode" expresses how the Downweb Line Rate is determined in a line-scan acquisition system.

The user specifies the Line Rate Mode by means of MultiCam parameter LineRateMode. Five Line Rate modes are identified in MultiCam:

LineRateMode

Description

CAMERA

Camera – The downweb line rate is originated by the camera.

PULSE

Trigger Pulse – The downweb line rate originates from a train of pulses applied on the line trigger input belonging to the grabber.

CONVERT

Rate Converter – The downweb line rate originates from a train of pulses applied on the line trigger input and processed by a rate converter belonging to the grabber.

PERIOD

Periodic – The downweb line rate originates from an internal periodic generator belonging to the grabber

EXPOSE

Exposure Time – The downweb line rate is identical to the camera line rate and established by the exposure time settings

LineRateMode = CAMERA

This mode is applicable exclusively for free-run permanent exposure – LxxxxSP – class of line scan cameras when LineCaptureMode=ALL. The grabber does not perform any sampling in the downweb direction; the downweb line rate is equal to the camera line rate. The camera line rate is entirely under control of the camera. Notice that most of the line scan cameras provide an internal line rate adjustment.

LineRateMode = PULSE

When the speed of motion is varying, the Downweb Line Rate should be slaved to this motion. To achieve this, a motion encoder is a good solution.
The motion encoder delivers an electrical pulse each time the moving web advances by a determined amount of length. The continuous motion results in a train of pulses the frequency of which is proportional to the web speed.
There exists another way to take knowledge of the web speed. In some applications, the motion is caused by a stepping motor controlled by pulses. The controlling train of pulses is also a measure of relative motion.
In both cases, the pulses are called line trigger pulses, and their repetition rate is the Line Trigger Rate. The line trigger pulses are applied to the frame grabber to determine the Downweb Line Rate .
Each line trigger pulse may result into the generation of one line in the acquired image. This means that the Downweb Line Rate is equal to the Trigger Rate.

LineRateMode = CONVERT

Alternatively to the "PULSE" mode, for more flexibility, the Line Trigger Rate may be scaled up or down to match the required Downweb Line Rate. The proportion between the two rates is freely programmable to any value lower or greater than unity, with high accuracy. This makes possible to accommodate a variety of mechanical setups, and still maintain a full control over the downweb resolution. The hardware device responsible for this rate conversion is called the rate converter. This device is a unique characteristic of Euresys line-scan frame grabbers.

LineRateMode = PERIOD

Other circumstances necessitate the Downweb Line Rate to be hardware-generated by a programmable timer, called the "periodic generator".

LineRateMode = EXPOSE

This mode is applicable exclusively for line rate controlled permanent exposure – LxxxxRP – class of line scan cameras when LineCaptureMode=ALL. The grabber does not perform any sampling in the downweb direction; the downweb line rate is equal to the camera line rate. The camera line rate is entirely under control of the grabber through the exposure time settings.

Important Notes

This mode is the default and recommended mode for LxxxxRP class of cameras on Grablink Avenue and Grablink Express.

This mode is not available on Grablink Value, Grablink Expert 2 and Grablink Quickpack ColorScan. On these boards...

  1. Use LineRateMode=PERIOD instead
  2. Specify the desired exposure time through Period_us
  3. Assign a value to Expose_us that is smaller than the desired exposure time.