1. Introduction
This application document describes how to trigger and synchronize two Chronos high-speed cameras of different models. The procedures can be extended to trigger or synchronize more than two cameras regardless of their model.
Such a situation occurs when a camera user needs to visualize a particular scene from two different angles to clarify the evolution of the phenomenon under scrutiny with an added level of detail.
The document contains three sections, 2.1 to 2.3, that describe how to trigger and synchronize a Chronos 4K12 and a Chronos 1.4 / Chronos 2.1-HD camera.
2.1 Triggering and synchronization using an external source, Shutter Gating. Suitable for applications where the user wants or needs to drive both cameras by an external source, i.e., a pulse delay generator or a function generator. The camera recording process can be triggered or synchronized to other event(s) like the triggering of a pulsed laser or a sensor.
2.2 Triggering and synchronization with a single pulse, Record End. This option is convenient in applications where a recording is ended by a single pulse of short duration. The pulse can be emitted by a microcontroller, a function generator or a pulse delay generator, and it signals the end of the event to be captured.
2.3 Triggering and synchronization using the trigger switch button, Record End. Used if the user wishes to control the end of the recording via the trigger switch button. It is recommended for cases where the frame rate is no higher than ~ 1,000 fps. At higher frame rates, for instance 5 or 10 KFPS, a large number of frames are recorded by the time the user presses the Trigger Switch button. It is challenging and time consuming to find the event of interest among all of those images.
In this document the Chronos 4K12 unit, referred to as the driving camera, drives a Chronos 1.4 camera, the driven device. A Chronos 2.1-HD can also be used as a driven camera. Please refer to the user manual to check the differences between the two models.
At the end of each section, the evaluation of the synchronization of the two cameras is presented. We observe the collision of a water droplet on a pool of water in a glass container 41 mm in diameter. The droplet is dispensed at the tip of a syringe located 260 mm about the surface of the glass. This simple test is repeatable, easy to implement and presents fast events that occur in µs scale, for instance the droplet ejection at the droplet landing and the jet break up. Thus it allows us to make comparisons of the temporal agreement between the sequences captured by the driving and the driven cameras.
2. Triggering and synchronization methods
2.1 Synchronization of two cameras using an external source, Shutter Gating
2.1.1 Settings
In this section a setup is described to synchronize a 4K12 Chronos camera and a 1.4 Chronos camera. There are a couple of characteristics that make this case different from sections 2.2 and 2.3
The recording of both cameras is initiated and ended manually
The driving camera receives the input signal from an external device and then conveys it to the driven camera.
Note that synchronization implies recording each frame at the same time with each camera. A sample test will be presented to show the synchronization of the two devices, see figure 9.
For this example both cameras are set to run at 1000 fps. They are driven by a function generator, Rigol DG 1022, at 1000 fps and with a duty cycle of 5%. Thus in each pulse, the driving camera’s sensor is exposed for 50 µs. The function generator provides a train of 2001 pulses to the driving camera when enabled by the user. In turn the driving input is conveyed to the driven camera. The frequency and duty cycle set at the function generator define the frame rate and the exposure time at which the test is conducted, respectively.
Function generator settings
Frequency: 1000 Hz
Duty cycle: 5%
Number of pulses: 2001
Figure 1 displays the schematic diagram for synchronizing a Chronos 4K12 and a Chronos 1.4 / Chronos 2.1-HD camera:
Figure 1. Schematic diagram for the synchronization of Chronos 4K12 and Chronos 1.4 / Chronos 2.1-HD.
The triggering device can be connected in parallel to port 1 of the 4K12 camera through the Y-connector, seen on the left in figure 2, and to the IO1 BNC port located on the side panel of the 1.4 and 2.1-HD cameras. The Frame Sync Output signal from the driving unit can be transferred from port 2 of the 4K12’s Y-connector to port IO2 (pins 5 and 6) or port IO3 (pins 7 and 8) of the driven unit. The phoenix connector with a BNC extension connected to pins 5 and 6 of a 1.4 camera can be seen on the right side in figure 2.
If you want to keep track of the camera signals in an oscilloscope, you can use a BNC tee from the Y-connector’s port 2 of the driving camera and feed it to an oscilloscope. For the driven unit, set IO3 (pins 7 and 8) to Shutter Gating and connect a BNC cable from the driving unit’s port 2 to pins 7 and 8. Then set port 2 to Frame Sync Out in the driven unit’s triggering menu and connect a BNC cable from pins 5 and 6 to your oscilloscope.
Figure 2. Left, Y-connector of the Chronos 4K12 driving unit. Right, BNC connector attached to pins 5 and 6 of the driven unit.
The driving and driven cameras run on a different firmware platform. They process the initial triggering scheme in a different manner. Despite the driven camera running with the input signal provided by the driving camera, it is necessary to make the record length of the driven camera three frames longer than that of the driving camera.
Notice that due to firmware differences, the number of frames to be captured is different in the driving and in the driven camera. When the footage is reviewed, both cameras must display the same event in the same frame, as can be seen in figures 9, 16 and 23. For the tests performed, the overlay feature of the cameras is used. This helps in the spatial correlation of the images captured. The images can be saved at a TIFF sequence, which preserves the text overlay in each frame saved.
Keep in mind that the Chronos 1.4 camera saves a TIFF sequence with the first two images moved to the back of the sequence and the third image copied at the end of the sequence. This is a known issue when a sequence is saved from the first frame. Thus the total number of frames saved ends up being N + 1. The image sequences from the two cameras need to be matched with the help of software.
Figures 3 and 4 display the settings used. Figure 3, left side, portrays the trigger settings. Channel 1 is set to Shutter Gating. Channel 2 is set to Frame Sync Output, this is the driving signal that is conveyed to the driven camera. The delay is enabled, thus the input signal from the external device is delayed 8 µs to line up with the time when the sensor is exposed.
On the right side of figure 3 the Record settings menu is presented. The highest ISO, 400, was used as it provides higher sensitivity without introducing significant noise to the images. However, the frame rate and the exposure time, as mentioned earlier, will be set by the frequency and the duty cycle of the external device, respectively.
Note: Make sure the frequency fed to the camera does not exceed the maximum frame rate for the resolution used. You can press the Max button to set the maximum frame rate and verify it is higher than the frequency to be fed to the camera.
Figure 3. Driving camera. Left, trigger settings. Right, record settings.
From the Record Setting screen, the Record Modes button allows the user to set the number of frames to be recorded; this is shown in figure 4, left side. Once the settings have been confirmed, the Main screen, seen in figure 4 on the right side, shows the channel settings in the upper right side and the record length in the upper left side of the screen. In addition, the lower part of the screen displays the resolution selected, the frame rate and the exposure entered in the record settings menu. The NO SIGNAL sign indicates that the camera is waiting for a signal, it appears when the Shutter Gating option is enabled and the camera is waiting for a signal.
Figure 4. Driving camera. Left, record modes screen. Right, main screen
The following images depict the settings used in the driven camera. Figure 5, left side, shows the trigger settings menu of the 1.4 camera. On the right side the number of frames to be captured can be seen.
Figure 5. Trigger settings of the driving camera
Figure 6 portrays the record settings screen of the driven camera. The frame rate is set at 1000 fps, lower than the maximum frame rate for the resolution used, 1280 X 1024.
Figure 6. Record settings, driven camera.
2.1.2 Procedure
Connect the camera according to your triggering device according to figure 1. The physical ports of the driving and the driven camera can be seen in figure 2.
Next, set up the driving and driven cameras’ record and trigger settings, as depicted in figures 3-6.
When ready carry out the following:
Press the record button of the driving camera
Press the record button of the driven camera
Feed the signal from the external device to the cameras
When the test is completed, press the stop button of the driven camera
Press the stop button of the driving camera
Review the footage and make sure both cameras have acquired the footage at the same frame number
If needed, enable the overlay text function to see the frame number on each frame
Save the footage from captured by each camera
2.1.2 Validation
The synchronization of the two cameras is evaluated by recording the collision of a water droplet on a pool of water. The input signal and the Frame Sync Output signal from each camera is evaluated in an oscilloscope, Rigol DS 1104 100MHz.
Figure 7. Left, 2001 input and camera signals. Right, the trigger time
Figure 7 portrays the oscilloscope signals. The yellow, green and magenta traces correspond to the input signal from the oscilloscope, the output signal from the 4K12 camera and the output signal from the 1.4 Chronos camera, respectively.
In figure 7, left side, the traces appear well aligned. Also, the cameras feed a signal to the oscilloscope as long as the function generator feeds the signal into the driving camera and the signal is transferred to the driven camera. A closer look shows the time delay between the input signal and the two cameras. The time delay between the input signal and the driving camera’s output signal is 8 µs, as expected since the delay option was enabled in the trigger settings menu of the driving camera, see figure 3. The time delay between the signal outputs of the cameras is 4 µs, shorter than the exposure time and significantly shorter than the interframe time, 1 ms.
Figure 8 presents the last pulse emitted by the function generator, yellow trace. Notice that the time delay between the cameras remains at 4 µs, thus there is no drift between the signals.
Figure 8. The last pulse emitted by the function generator and the signal output from the driving and the driven cameras.
Figure 9, upper row, depicts selected images from the saved TIFF sequence from the driving camera, from left to right, the droplet just before and after impacting on the liquid pool and a satellite droplet just before and after detaching from the liquid jet. The bottom row of figure 9 presents the same events seen in the upper sequence. The sequence was recorded by the driven camera. The overlay text displays the frame number in both sequences. The same frame number is displayed in each image in both sequences.
Figure 9. Upper row. Water droplet impact captured by the driving camera, 4K12. Lower row, the same phenomenon captured by the driven camera, 1.4 Chronos.
2.2 Triggering and synchronization with a single pulse, Record End.
2.2.1 Settings
The setup described here shows how to trigger and synchronize a 4K12 Chronos camera and a 1.4 Chronos camera. The method has the following features:
The recording of both cameras is initiated manually
The driving camera conveys its sensor signal to the driven camera, thus both cameras have the sensor exposed at the same time
The recording ends when a single pulse from an external device is sent to each camera
In the test described both cameras are synchronized as they record each frame at the same time. Furthermore, an external device provides the trigger signal that ends the record process at the same time in both cameras.
Also in this section a sample test is presented to show the synchronization of the two devices, see figure 16.
Figure 10 portrays a schematic diagram of the setting for the Record End option. Notice the red line connecting the driving and driven cameras.
Figure 10. Schematic diagram for the triggering and synchronization of Chronos 4K12 and Chronos 1.4 / Chronos 2.1-HD cameras, Record End option.
The driving camera is set to operate in Record End mode, the trigger settings can be seen in figure 10. Both cameras are set to operate at 1000 fps and exposure time is 50 µs in both cameras. The record settings of the driving camera are displayed in the Record Settings menu, figure 11, left side.
Figure 11. Driving camera screen shots. Left, trigger settings. Right, record settings.
Figure 12. Driving camera. Left, record modes screen. Right, main screen
Next, figures 13 and 14 portray the trigger and record settings of the driven camera. Notice that both cameras are set to Record End mode in channel 1, the feeding signal from the device that provides the single pulse. Channel 2, Frame Sync Output, is sent to the oscilloscope. The signal from the driving camera is fed to the driven camera through Input 3, set to Shutter Gating.
Figure 13. Driven camera, trigger settings.
Figure 14. Driven camera, record settings.
2.2.2 Procedure
Connect the camera according to your triggering device as shown in figure 10. The physical ports of the driving and the driven cameras can be seen in figure 2.
Next, set up the driving and driven cameras’ record and trigger setting, as shown in figures 11-14.
With record and trigger setting in place in the driving and driven cameras the following procedure can be followed:
Press the record button of the driven camera, so it waits for the signal from the driving camera.
Press the record button of the driving camera.
Execute and record the event as needed.
When the test is completed, send the single pulse to the camera, or wait for it to be sent by the external device.
Review the footage captured by each camera. Check that both cameras have acquired the footage at the same frame number.
Enable the overlay text function if needed. This helps to correlate the frame number of the two cameras.
Save the footage.
2.2.3 Validation
The synchronization of the two cameras is evaluated in the same fashion described in section 2.1.3. The input signal and the Frame Sync Output signal from each camera is also recorded by the oscilloscope.
Figure 15. Left, single pulse, yellow trace, and camera signals. Right, the trigger time.
Figure 15, left side, depicts the trigger pulse that ends the recording, in yellow, the signal output from the driving and the driven cameras in blues and magenta, respectively. The output signal from the cameras appear to be well aligned with each other. A close up of the time around the time the trigger pulse is emitted can be seen on the right side of figure 14. The pulse takes place between the two exposures of the cameras, thus the temporal uncertainty of the end of the recording is ±1/2 of the interframe time. Yet, the time delay between the two cameras is ~ 4 µs as portrayed in figure 16.
Figure 16. The time delay between the signal outputs from the driving camera, blue trace, and the driven camera, magenta trace.
Figure 17 shows selected pictures of the sequence captured. The upper row are images captured by the driving camera. The lower row are the pictures recorded by the driven camera. Both sequences display the same frame number and the same event.
Figure 17. Water droplet impact captured by the driving camera, Chronos 4K12, upper row and the driven camera, Chronos 1.4, bottom row.
2.3 Triggering and synchronization using the trigger switch button, Record End mode
2.3.1 Settings
Similar to the previous section, the setup described here allows the user to trigger and synchronize a 4K12 Chronos camera and a 1.4 Chronos camera. The features of the setup are the following:
The recording of both cameras must be started manually
The driving camera transmits its sensor signal to the driven camera, hence both cameras expose their sensors at the same time
The recording in each camera ends when the user presses the trigger switch button
Both cameras capture the same event at the same time, same as in section 2.2. However, in this test the trigger switch button provides the trigger signal to both cameras to end the recording.
This section describes the way to end a recording with a trigger switch button. The record process will end simultaneously and the cameras are set to operate as in the previous two sections in the driving (4K12) - driven (Chronos 1.4) camera configuration. This represents an alternative when there is no external device that provides an external signal or even a single pulse, yet the results will show that the cameras are properly synchronized.
Figure 18 depicts a schematic diagram of the setting for the Record End option. Notice the red line connecting the driving and driven cameras. This is needed to convey the driving camera’s Frame Sync Output signal to the driven camera.
Figure 18. Schematic diagram for the triggering and synchronization of Chronos 4K12 and 1.4 or 2.1 cameras using the Trigger switch button, Record End option.
For this example, the cameras were adjusted with the following settings:
Driving camera, Chronos 4K12
Frames to record - 2000
FPS - 1000
Exposure time - 50 µs
Record Mode - Normal
Driven camera, Chronos 1.4
Frames to record - 2000
FPS - 1000
Exposure time - 50 µs
Record Mode - Normal
In this test, as in section 2.2, the driven camera also needs to start recording first.
Figure 19. Driving camera screen shots. Left, trigger settings. Right, record settings. Notice that the Debounce option is enabled to prevent spurious triggers to affect the record end.
The trigger settings of the driving camera and the Record settings can be seen in figure 19. The record mode, where the number of frames to be captured is entered, and the main screen are displayed in figure 20.
Figure 20. Driving camera. Left, record modes screen. Right, main screen
The trigger and record settings of the driven camera can be seen in figures 21 and 22, respectively.
Figure 21. Driven camera, trigger settings.
Figure 22. Driven camera, record settings.
2.3.2 Procedure
Connect the camera according to your trigger switch button as depicted in figure 18. Refer to the images of the y-connector and the Phoenix connector, figure 2, of the driving and the driven cameras to make the cameras communicate with each other.
Next, set up the driving and driven cameras’ record and trigger setting, as depicted in figures 19-22.
With record and trigger settings in place in the driving and driven cameras, the devices are ready to start the recording.
The procedure to carry out a synchronized recording using a trigger switch button is the same as that when a single pulse is used to end the recording.
Press the record button of the driven camera, so it waits for the signal from the driving camera.
Press the record button of the driving camera.
Execute and record the event as needed.
When the test is completed, press the trigger switch button.
Review the footage captured by each camera. Check that both cameras have acquired the footage at the same frame number.
Enable the overlay text function if needed. This helps to correlate the frame number of the two cameras.
Save the footage.
2.3.3 Validation
Figure 23. Left, the trigger from the trigger switch button, yellow trace, and camera signals. Right, the time when the trigger occurs.
Figure 23 presents the signals of the trigger switch button, the driving camera and the driven camera in yellow, blue and magenta traces, respectively. In this case the signal from the trigger switch is not as uniform as it was shown in the previous section. Due to this, it is advised to use the debounce function. A close up of the time around the time the trigger occurs shows that the time delay between the signals produced by the driving and the driven cameras is 4 µs, which is the same time delay reported in the previous sections.
Figure 24. Selected images of the water droplet impact on a pool of liquid. Top row, images captured by the driving camera, 4K12. Bottom row, frames recorded by the driven camera, Chronos 1.4.
Figure 24 presents selected images captured by the driving camera, upper row, and the driven camera, lower row. Notice in the lower left corner of the frames that the frame number is the same in both sequences. Also, the first frame of each sequence depicts the droplet just as it is about to or just impacting on the pool of liquid. The third picture portrays the leading part of the jet about to detach and it is detached right in the following frame. Both image sequences display the same frame number.
3. Conclusions
The present document describes three possible schemes to trigger and synchronize a Chronos 4K12 camera and a Chronos 1.4 / Chronos 2.1-HD camera. The three options are described to provide the users with a suitable solution for their video recording needs. It has been shown that the cameras can capture the same event simultaneously.
If you have any questions regarding the setting of your imaging system, do not hesitate to contact us at [email protected]
4. Useful links
The following documents may be useful in case you have questions regarding the use, settings or physical features of the 4K12, 1.4 or the 2.1-HD cameras.