Trigger Modes for Area-Scan Cameras

Emergent Vision Technologies’ area-scan cameras offer different triggering modes, ranging from simple triggerless acquisition to precise and synchronized software, PTP, and hardware triggering. Below, we detail these modes and provide configuration guidelines to help you effectively set up your high-speed camera system.

See also Trigger Modes for Line-Scan Cameras.

Mode AS-A: Triggerless acquisition

If you don’t need to synchronize frame capture with external events or devices, you can configure an area-scan camera for triggerless acquisition. To start and stop frame capture, simply use the acquisition start and stop commands or use the corresponding features in eCapture.

The following figure shows the elements of triggerless acquisition.

Figure 1: Area-scan trigger mode AS-A: Triggerless acquisition

To configure an area-scan camera for triggerless acquisition:

1. Set the following parameters:
   • acquisition mode: continuous
   • trigger mode: off
   • trigger source: software
2. Set the following parameters as needed:
   • frame rate
   • exposure length
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 AS-B: Software triggers

In software trigger mode, you trigger frame capture by executing the trigger software command.

Note: If a camera receives a trigger before it’s ready to start a new capture, it ignores the trigger.

The following figures show the elements of software triggers with different frame counts.

Figure 2: Area-scan trigger mode AS-B: Software trigger with frame count = 1

Figure 3: Area-scan trigger mode AS-B: Software trigger with frame count = 2

To configure an area-scan camera with software triggering:

1. Set the following parameters:
   • acquisition mode: multiframe
   • trigger mode: on
   • trigger source: software
2. Set the following parameters as needed:
   • acquisition frame count
   • frame rate (ignored with acquisition frame count = 1)
   • exposure length
3. Disable PTP mode.
4. Enable frame capture by executing the acquisition start command.
5. To start frame capture, execute the trigger software command.
   The acquisition frame count setting determines when frame capture stops.
6. To disable frame capture, execute the acquisition stop command.
   Note: When the camera gets the acquisition stop command, it finishes capturing the number of frames specified by the acquisition frame count parameter.

Mode AS-C: PTP triggers

To precisely synchronize multiple cameras using the precision time protocol (PTP), you set the same PTP acquisition gate time for all the cameras. When the cameras simultaneously reach gatetime, they will begin frame capture, and each frame capture will be synchronized with the PTP clock.

The following figure shows the elements of PTP triggers.

Figure 4: Area-scan trigger mode AS-C: PTP trigger

To configure an area-scan camera with mode PTP triggering:

1. Set the following parameters:
   • acquisition mode: multiframe
   • trigger mode: on
   • trigger source: software
   • acquisition frame count: 1
2. Set the following parameters as needed:
   • frame rate
   • exposure length
3. Enable PTP mode on the camera, setting it to one step or two step, depending on the packets from your PTP grandmaster clock.
4. Wait until their PTP status value is slave, which means the PTP clock has been acquired and the cameras now have a valid and reliable PTP clock.
5. Get the current time from any camera:
   • Use the latch timestamp command to store the current time in two registers.
   • Use the GEV timestamp value feature to read the current time.
6. Set the PTP acquisition gate time for all the cameras to the current time plus a margin, such as 5 seconds, to account for possible system delays.
7. After setting the gate time but before reaching it, enable frame capture by executing the acquisition start command.
   When gate time occurs, frame capture begins. Also at that moment, the camera resets the gate time to the previous gate time plus the frame time. In this way, the camera continuously grabs frames that are each synchronized with the PTP clock.
8. To stop frame capture, execute the acquisition stop command.
   Note: When the camera gets the acquisition stop command, it finishes capturing the frame.

Mode AS-D1: Hardware triggers with internal exposure settings

In hardware trigger mode AS=D1, you trigger frame capture with an input signal on a GPI_n pin and control the duration of each frame Internally with the camera’s exposure setting.

Note: If a camera receives a trigger signal before it’s ready to start a new capture, it ignores the trigger.

The following figures show the elements of hardware triggers with internal exposure settings and different frame counts.

Figure 5: Area-scan trigger mode AS-D1: Hardware trigger with internal exposure setting and frame count = 1

Figure 6: Area-scan trigger mode AS-D1: Hardware trigger with internal exposure setting and frame count = 2

To configure an area-scan camera with hardware trigger mode AS-D1:

1. Set the following parameters:
   • acquisition mode: multiframe
   • trigger mode: on
   • trigger source: hardware
   • GPI start exposure mode: GPI 4 (example value)
   • GPI start exposure event: rising edge (example value)
   • GPI n debounce count: 50 (example value to reduce noise in signal detection)
2. Set the GPI end exposure mode to internal.
3. Set the following parameters as needed:
   • acquisition frame count
   • frame rate (ignored with acquisition frame count = 1)
   • exposure, which determines the duration of each frame

After configuring the camera, frame capture begins when it receives a rising edge on GPI 4 (based on the example values). Frame capture ends when the number of frames specified by the acquisition frame count are captured.

Mode AS-D2: Hardware triggers with external exposure settings

In hardware trigger mode AS-D2, you trigger frame capture with an input signal on a GPI_n pin and control the duration of each frame externally with the length of the input signal pulse.

Note: If a camera receives a trigger signal before it’s ready to start a new capture, it ignores the trigger.

The following figure shows the elements of hardware triggers with external exposure settings.

Figure 7: Area-scan trigger mode AS-D2: Hardware trigger with external exposure setting

To configure an area-scan camera with hardware trigger mode AS-D1:

1. Set the following parameters:
   • acquisition mode: multiframe
   • trigger mode: on
   • trigger source: hardware
   • GPI start exposure mode: GPI 4 (example value)
   • GPI start exposure event: rising edge (example value)
   • GPI n debounce count: 50 (example value to reduce noise in signal detection)
2. Set the GPI end exposure mode to GPI 4 (example value)
3. Set the GPI end exposure event to falling edge (example value)

After configuring the camera, it captures a frame whenever it receives a rising edge on GPI 4 (based on the example values). Each frame’s exposure duration is determined by the length of the pulse on GPI 4.

In this mode, cameras ignore their internal acquisition frame count, frame rate, and exposure settings.

Hardware trigger delays

The trigger delay parameter provides a precise and adjustable time delay between when a camera receives a hardware trigger signal and when it captures an image. It allows precise timing when working with external sensors, lighting, or other equipment that you could trigger with the same signal, ensuring all components work synchronously.

The following figure shows the elements of hardware triggers with trigger delays.

Figure 8: Trigger delay with hardware trigger mode AS-D1 and frame count = 2

To delay frame capture, set the trigger delay parameter as needed.

GPO strobe mode

When a camera is connected to lighting through a GPIO output pin, such as GPO 1, you can warm up the lighting before exposure starts by setting the output pin to strobe mode and setting a trigger delay for the camera’s exposure. This triggers the lighting before frame capture begins.

Note: GPO strobe mode is typically used only when a trigger initiates the capture of a single frame.

The following figure shows the elements of hardware triggers with GPO strobes and trigger delays.

Figure 9: GPO strobe and trigger delay with hardware trigger mode AS-D1 and frame count = 1

To configure strobe mode on GPO_n, where “n” denotes a pin number, set the GPO n mode parameter to strobe.

The strobe signal on GPO_n:

• Starts when the camera receives any kind of frame trigger request.
• Ends when the frame exposure ends.