Trigger Modes for Line-Scan Cameras

Emergent Vision Technologies’ line-scan cameras support various triggering methods, depending on the desired mode for triggering frames and lines. The default mode uses internal triggers, while other modes use external hardware triggers. You can control line time internally or with an external encoder, which is more common. Using external triggers and encoders attached to conveyor belts or other motion systems allow more precise control and synchronization of imaging.

Note: Line-scan cameras only support continuous acquisition mode and so don’t use an acquisition frame count parameter.

See also Trigger Modes for Area-Scan Cameras.

Mode LS-A: Triggerless acquisition

If you don’t need to synchronize frame and line capture with external events or devices, you can configure a line-scan camera for triggerless acquisition using the camera’s software features and commands.

Key features for trigger mode LS-A:

• The acquisition start and stop commands start and stop image acquisition
• The frame rate feature controls the start of each frame
• The height feature controls the number of lines in each frame
• The exposure feature controls the duration of each line capture
• The frame rate and line time sync feature evenly spaces the lines (and extends the frame) along the frame time by adjusting the line time according to the frame rate (the line time setting is ignored)

Figure 1: Line-scan camera trigger mode LS-A: Triggerless acquisition

To configure a line-scan camera to use triggerless acquisition:

1. Set the following parameters:
   • trigger mode: off
   • trigger source: software
   • frames rate and line time sync: enabled
2. Set the following parameters as needed:
   • frame rate
   • height of the frame
   • exposure duration of each line capture
3. To start frame capture, execute the acquisition start command or use the corresponding feature in eCapture.
4. To stop frame capture, execute the acquisition stop command or use the corresponding feature in eCapture.

Mode LS-B: Hardware frame trigger and internal line time setting

You can use signals from an external hardware device or system to trigger each frame and the camera’s line time setting to trigger each line capture.

Key inputs and features for trigger mode LS-B:

• Hardware trigger signals control the start of each frame, with each frame starting when the signal on the specified pin rises (or falls)
• The line time feature controls the start of each line capture
• The exposure feature controls the duration of each line capture

Figure 2: Line-scan camera trigger mode LS-B: Hardware frame trigger and internal line time setting

To configure a line-scan camera to use a hardware frame trigger and internal line time setting:

1. Set the following parameters:
   • trigger mode: on
   • trigger source: hardware
   • GPI start frame mode: GPI 1 (example value for the trigger signal pin)
   • GPI start frame event: rising edge (example value for the trigger event)
   • GPI 1 debounce count: 50 (example value to reduce noise in signal detection)
   • line time: 1000 (Example value for the number of camera clock cycles used to scan one line. The 10G and 25G cameras have 150 MHz clocks, whereas 100G cameras  have 400 MHz clocks.)
2. Set the line exposure duration as needed.

Mode LS-C: Hardware frame trigger and encoder line-scan trigger

You can use signals from an external hardware device or system to trigger each frame and pulses from an encoder to trigger each line capture.

Key inputs and features for trigger mode LS-C:

• Hardware trigger signals control the start of each frame, with each frame starting when the signal on the specified pin rises (or falls)
• Encoder pulses control the start of each line capture
• The exposure feature controls the duration of each line capture

Figure 3: Line-scan camera trigger mode LS-C: Hardware frame trigger and encoder line-scan trigger

To configure a line-scan camera to use a hardware frame trigger and encoder line-scan trigger:

1. Set the following parameters:
   • trigger mode: on
   • trigger source: hardware
   • GPI start frame mode: GPI 1 (example value for the trigger signal pin)
   • GPI start frame event: rising edge (example value for the trigger event)
   • GPI 1 debounce count: 50 (example value to reduce noise in signal detection)
   • encoder mode: on (enables encoder mode)
   • encoder line multiplier: 1 (example value that affects the line trigger pulse rate) 
   • encoder line divider: 4 (example value that affects the line trigger pulse rate)
2. Set the line exposure duration as needed.

Mode LS-D: Encoder frame and line-scan triggers

You can use pulses from an encoder to trigger each frame and line capture.

Key inputs and features for trigger mode LS-D:

• Encoder pulses control the start of each frame
• Encoder pulses control the start of each line capture
• The exposure feature controls the duration of each line capture

Figure 4: Line-scan camera trigger mode LS-D: Encoder frame and line-scan triggers

To configure a line-scan camera to use encoder frame and line-scan triggers:

1. Set the following parameters:
   • trigger mode: on
   • trigger source: hardware
   • GPI start frame event: encoder frame divider (the encoder provides pulses that are converted to frame triggers)
   • encoder mode: on (enables encoder mode)
   • encoder line multiplier: 1 (example value that affects the frame and line trigger pulse rates) 
   • encoder line divider: 4 (example value that affects the line trigger pulse rate)
   • encoder frame divider: 24000 (example value that affects the frame trigger pulse rate)
2. Set the line exposure duration as needed.

Mode LS-E: Encoder frame and line-scan triggers and hardware pulses

You can use pulses from an external hardware device or system to enable image acquisition and use pulses from an encoder to trigger each frame and line capture.

Key inputs and features for trigger mode LS-E:

• Hardware pulses enable or mask frame and line capture
• Encoder pulses control the start of each frame
• Encoder pulses control the start of each line capture
• The exposure feature controls the duration of each line capture

Figure 5: Line-scan camera trigger mode LS-E: Encoder frame and line-scan triggers and hardware pulses

To configure a line-scan camera to use encoder frame and line-scan triggers and hardware pulses:

1. Set the following parameters:
   • trigger mode: on
   • trigger source: hardware
   • GPI start frame mode: GPI 1 (example value for the trigger signal pin)
   • GPI start frame event: rising edge (example value for the trigger event)
   • GPI 1 debounce count: 50 (example value to reduce noise in signal detection)
   • encoder mode: on (enables encoder mode)
   • encoder line multiplier: 1 (example value that affects the frame and line trigger pulse rates) 
   • encoder line divider: 4 (example value that affects the line trigger pulse rate)
   • encoder frame divider: 24000 (example value that affects the frame trigger pulse rate while the GPI_Start_Frame_Event is still active)
2. Set the line exposure duration as needed.

Converting encoder pulses to trigger pulses

You can use an encoder to precisely synchronize the movement of objects and material with a line-scan camera’s line and frame triggers.

To adjust the line trigger pulses for trigger modes LS-C, LS-D, or LS-E, configure the line multiplier and line divider settings.

line trigger pulse rate = forward motion pulse rate × (line multiplier ÷ line divider)

For example, to configure a line trigger pulse rate that’s twice the rate of the forward motion pulses produced by the encoder’s pulses, set the line multiplier to 2 and the line divider to 1.

To adjust the frame trigger pulses for trigger modes LS-D or LS-E, configure the line multiplier and frame divider settings.

frame trigger pulse rate = forward motion pulse rate  × (line multiplier ÷ frame divider)

For example, to configure a frame trigger pulse rate that’s 3/50th the rate of the forward motion pulses produced by the encoder’s pulses, set the line multiplier to 3 and the frame divider to 50.

Note: Each trigger pulse is derived from the last forward motion pulse. If the forward motion of the objects or material has a constant speed, producing steady forward motion pulses, then the trigger pulses will be synchronized with the motion of the objects or material. However, if the speed fluctuates, the triggers will be less synchronized.

The following figure shows how the camera and its software convert encoder pulses to line trigger pulses and frame trigger pulses.

Figure 6: The camera and its software convert encoder pulses to line and frame trigger pulses