WEB Acquisition Mode

In the WEB acquisition mode, a unique acquisition sequence can be executed within the Channel activity period.

A WEB acquisition sequence acquires SeqLength_Ln contiguous lines. It is divided in contiguous phases, each phase acquiring PageLength_Ln lines. When SeqLength_Ln is not a multiple of PageLength_Ln, the last phase fills partially the surface.

The sequence and the first acquisition phase are initiated according to TrigMode. Subsequent acquisition phases are automatically initiated without any line loss.

BreakEffect specifies the behavior in case of a user break.

The WEB acquisition mode is the default mode enforced automatically by MultiCam for line-scan cameras; it can also be explicitly invoked by assigning value WEB to AcquisitionMode.

The first action is to define all MultiCam channel parameters before channel activation.

More specifically the following acquisition control parameters need to be configured:

Parameter	Value range
AcquisitionMode	WEB
TrigMode	IMMEDIATE, HARD, SOFTand COMBINED
BreakEffect	FINISH, ABORT
PageLength_Ln	1 ~ 65535
SeqLength_Ln	MC_INDETERMINATE and 1 ~ (PageLength_Ln × 65,535)

When invoking the WEB acquisition mode:

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ActivityLength is enforced to 1. The channel automatically goes inactive at the completion of the sequence.

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PhaseLength_Pg is enforced to 1. A single page is acquired during an acquisition phase.

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PageLength_Ln is automatically set to a working value. However, the page length can be enforced by setting PageLength_Ln. For more information see Setting Optimal Page Length.

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TrigMode establishes the starting condition of the sequence and consequently the starting condition of the first phase of the sequence. Possible values are IMMEDIATE, HARD, SOFT and COMBINED. The default MultiCam setting is IMMEDIATE.

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NextTrigMode is enforced to REPEAT. This ensures that no lines are missed between subsequent acquisition phases.

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The sequence length is specified by SeqLength_Ln. Assigning a value MC_INDETERMINATE enforces an indefinite WEB acquisition sequence. Assigning any value ≥ 1 enforces a finite WEB acquisition sequence.

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EndTrigMode is enforced to AUTO. The sequence terminates automatically after the acquisition of the specified number of pages. An indefinite acquisition sequence stops when the channel is forced to its inactive state.

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BreakEffect establishes the effect of a user break on the channel. When set to FINISH, it ensures the integrity of the last acquired phase —page— even when the user break event occurs during its execution; this is the default value. When set to ABORT, the effect of the user break is immediate (at line boundary); the current acquisition might be incomplete; the portion of image already acquired is available. When SeqLength_Ln is not a multiple of PageLength_Ln, the last acquired page is partially filled despite the FINISH setting.

Setting ChannelState parameter to ACTIVE activates the channel and arms the trigger circuit.

The WEB acquisition sequence will start after the first trigger event occurring after channel activation.

The origin of the trigger event is determined by the trigger condition as specified by TrigMode parameter.

Usually, the trigger event is immediate (TrigMode=IMMEDIATE) in order to start the acquisition sequence immediately. Alternatively soft trigger (TrigMode=SOFT) or hard trigger signal (TrigMode=HARD) or both can be selected (TrigMode=COMBINED). When hard trigger is specified, additional parameters TrigCtl, TrigEdge, TrigFilter and TrigLine define the trigger input.

To summarize the usage of trigger parameters, see Hardware Trigger.

Once the WEB acquisition sequence is started, the frame grabber acquires data lines continuously until the acquisition sequence is stopped.

The acquisition sequence is composed of one or more acquisition phases. During an acquisition phase the frame grabber stores data lines into one destination surface.

Destination surfaces contain an arbitrary number of lines as defined by parameter PageLength_Ln.

When a surface is filled, the acquisition continues automatically into the next available surface without any missing lines. This process repeats until a stop condition occurs.

Every time a surface is filled, the "MC_SIG_SURFACE_FILLED" signal is reported to the user. Parameter LineIndex reflects the number of lines already written in a partially filled surface. If SeqLength_Ln is not a multiple of PageLength_Ln, the last surface will be partially filled. A new surface is selected at each begin of acquisition phase.

Lines are acquired at a rate defined by the line trigger condition. When object speed is variable, it is convenient to generate a line trigger derived from a motion encoder.

For more information, see Line Trigger and Line-Scan Synchronization.

The WEB acquisition mode allows two methods to stop the sequence: Manual stop and Automatic stop.

If the scanned object has a finite length, the automatic stop method can be used to automatically stop the sequence after a predefined number of lines. This variant of WEB acquisition is named WEB Finite. In this case, the number of lines to be acquired needs to be specified before Channel activation.

More often the length of the object is unknown. Therefore, the manual stop method is required. In this case, the parameter SeqLength_Ln should be set to MC_INDETERMINATE, in order to define an infinite WEB acquisition sequence.

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Elapsed_Ln reports the number of acquired lines in the sequence.

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When the sequence length is defined (SeqLength_Ln≠MC_INDETERMINATE), Remaining_Ln reports the number of remaining lines in the sequence.