A considerable part of the power of the PhotoniQ is in its ability to acquire large amounts of data under very different conditions. Its flexibility and diverse functionality allow it to be used in applications that include bioaerosol fluorescence detection, particle sizing, flow cytometry, confocal microscopy, and gamma ray imaging. While the number and types of applications is extensive, the process used for data acquisition generally falls into one of two categories — stochastic or continuous. For stochastic systems, events of interest arrive randomly distributed in time, often following a Poisson distribution. The emphasis in a system of this kind is on collecting events uniformly over time at the fastest rate possible — it is usually not essential that every event be captured. Particle analysis applications such as bioaerosol detection and flow cytometry are typically in this category. Continuous systems on the other hand, are more concerned with reliably capturing all events over a predefined interval of time. Although the rate of event capture can also be critical, it is important that no events are missed during the acquisition interval. A scanned imaging system like confocal microscopy is an example of a continuous data acquisition system. Here events are more appropriately referred to as pixels and the acquisition interval as the scan period.
The PhotoniQ accommodates these two broad classes of data acquisition by employing two distinct data acquisition modes — particle and image. Particle mode is often used in stochastic data acquisition applications where the PhotoniQ is configured to optimally acquire random events in the fastest way possible over an indefinite period of time. Although the trigger source in these applications can sometimes supply the PhotoniQ with triggers at extremely high rates, the PhotoniQ will only accept a trigger if it can adequately acquire the event data across all channels, and transfer it to the PC. Any trigger that would result in an event that cannot be properly acquired and processed is rejected. This permits the PhotoniQ to operate at a relatively constant acquisition rate for an unlimited period of time. The Sustained Average Event Rate (SAER) is the figure of merit that describes the data acquisition performance of a PhotoniQ in particle mode. While a small data buffer in the PhotoniQ allows it to acquire several consecutive events that briefly exceed the SAER, the maximum average event acquisition speed is generally equivalent to this specification.
Unlike particle mode where priority is placed on acquiring events uniformly over time, image mode places priority on acquiring each and every pixel over the scan period (the image frame). Thought of another way, particle mode assigns priority to transferring all acquired data to the PC whereas image mode assigns priority to accepting all triggers. In a scanned imaging system each trigger corresponds to a pixel. Since the pixel rate in image mode can be quite high — sometimes much higher than the transfer rate to the PC — a large, fast data buffer is used by the PhotoniQ to store a complete frame of image data. Thus the PhotoniQ operates by accepting all triggers (pixels) up to the point where either the triggers stop (the end of the scan period) or its buffer becomes full, and transfers the acquired data to the PC. The Maximum Trigger Rate (MTR) defines the maximum rate of data acquisition in image mode. Provided that the input trigger rate does not exceed the MTR, the PhotoniQ will fill its buffer with each and every pixel until it is full. Transfer of the image to the PC takes place at a rate equal to the SAER. Since in many situations the PC transfer time can exceed the image scan period, it is important that the PhotoniQ buffer be sized to hold at least one complete image.
For a detailed discussion on PhotoniQ's acquisition modes, see the following application note. PhotoniQ: Data Acquisition Modes