First, you need to explain what the external sensory inputs are for sensor (A) as well as for sensor (B). You may design sensor (A) as a threshold value or peak detector, with a secondary circuit to window the signals in sensor (B) for a pre-determined amount of time (which may be dependent on the threshold value selected, or the peak value for each trigger). This approach can be strictly hardware based. However, in these days and age, I would use a combination of hardware and software implementation, keeping the hardware simple with some mixed signal electronics while unleashing the flexibility of software engineering.

yes, simply the (A) sensor will be gaseous sensor which suppose to trigger (B) sensor optical or camera sensor . As u said exactly I want to put peak point to (A) that trigger (B) in real time . Do u recommend a hardware like connector and software for that purpose ?

In this case, the easiest approach is to interface your gas sensor with a multifunctional I/O (with ADC) board, and once a peak is detected, sends a trigger signal from your video card with the control I/O to your camera to start recording. You can code how and when you want to stop streaming data from the camera, either by a fixed time period, or when the gas sensor signal returns to zero (or any other threshold values, etc.). Both the MIO and video card may come with PCI or PCI express interface. In the absence for the need of a PCI-based video card, some cameras may be custom-interfaced to their own controller unit, which you may communicate through HDMI, ethernet, Wifi, etc.

Thank you very much, I will try to follow that and achieve something . I appreciate that