Common working modes and triggering methods of industrial cameras
November 11, 2023
Common working modes of industrial cameras are generally divided into:
Timing synchronization mode
Trigger mode: After receiving the external trigger command, the camera starts to expose according to the agreed time, and outputs one frame of image after the exposure is completed.
Continuous mode: The camera automatically and continuously performs exposures according to the agreed time and outputs images continuously.
Synchronous mode: After receiving the same trigger command, multiple cameras or multiple cameras and other devices will perform simultaneous exposure according to the agreed time and are strictly synchronized.
Timing synchronization mode: Based on the synchronization mode, the concept of absolute time is further added
Among them, the trigger mode is divided into:
Trigger mode: internal trigger, external trigger
Internal trigger mode: The camera collects images through signals given internally by the device;
External trigger mode: The camera collects images through external signals, which can be software signals/hardware signals, etc.;
Soft trigger: The trigger signal is given by the host connected to the camera;
Hard trigger: The trigger signal is given by an external device, usually a level pulse, and the trigger polarity can be selected;
Advantages and Disadvantages:
Soft trigger: easy to use, but the trigger speed and measurement accuracy are generally not as good as hard trigger;
Hard trigger: high precision, can flexibly adjust trigger signal frequency, duty cycle, etc. However, there are difficulties in wiring and use;
How to generate a trigger
In trigger mode, the trigger signal is the only condition for starting the camera exposure. The trigger signal can be generated by software (there is a special interface for generating software trigger signals) or by external hardware (mechanical switch/electronic sensor/PLC/single chip microcomputer/ IO card) is generated. We call these two methods software triggering and hardware triggering.
In the SDK, there is a dedicated interface for generating software trigger signals, and you can also set the number of frames for a trigger.
Hardware trigger (external trigger)
The external trigger input terminals are labeled TRIG+ and TRIG- (please check the line sequence definition table for the corresponding line colors). The camera uses optocoupler isolation internally and can identify rising edge, falling edge, double edge, high level, and low level. There are several kinds of signals. The methods for generating these signals are as follows:
One rising edge: when the voltage at both ends of TRIG+ and TRIG- changes from 0V to 5~24V, it changes once;
One falling edge: when the voltage at both ends of TRIG+ and TRIG- changes from 5~24V to 0V, it changes once;
A double edge: a rising edge plus a falling edge;
High level: The voltage at both ends of TRIG+ and TRIG- continues to maintain 5~24V;
Low level: The voltage at both ends of TRIG+ and TRIG- remains 0V;
Edge triggered mode. You can select the upper edge or lower edge as the trigger condition on the interface. When the trigger terminal receives a valid trigger signal, the camera starts to collect a frame of images and transmits it to the host. Each valid edge corresponds to a trigger, and only one frame of image is output. Before the last frame of image acquisition is completed, repeated trigger signals will be ignored. For example, if the camera's exposure time is set to 10 milliseconds and the effective trigger signal is set to rising edge trigger, then within 10 milliseconds, even if there are multiple rising edge signals, only one frame of image will be triggered.
Level triggered mode. You can select high level or low level as the trigger condition on the interface. When a trigger signal is at a valid level, the camera starts to collect a frame of image and transmits it to the host. After the frame collection is completed, if the signal is still at a valid level, the camera starts to collect the next frame of image and transmits it to the host until the trigger The signal changes to an inactive level.
Hard triggers are divided into:
Common trigger signals:
3.RS485 (RS422) differential level.
4.LVDS (644) differential level.
5. Optocoupler signal
Special voltage trigger signal (24V, 12V, etc.)