DVR Express Core Timing Information

DVR Express Core Timing Information

Resolution/Precision
The Core DVRs apply timestamps to incoming frames regardless of whether PC Time is being used, or another timing reference (e.g. IRIG-B or GPS etc.).  Regardless of the source, the timestamps have the same resolution/precision.  This is the number of decimal points of the timestamp.  All timestamps are applied with 100ns resolution/precision, but software settings determine how many decimal places are shown.  CoreView allows you to display up to 6 decimal points (down to microseconds) whereas Streams 7 allows you to display only up to 3 decimal points (down to milliseconds). However, both allow you to export timestamps into a text file for post-processing analysis, and these are provided with 7 decimal points (100ns).

Receiver Accuracy
Timestamp accuracy refers to how accurate the timestamps are, relative to a time reference.  This depends heavily on the receiver being used.  A GPS receiver may claim an accuracy within +/- 100ns of GPS time but that would also depend on the number of satellites locked, signal quality, and the quality of the components used in the receiver.

DVR Accuracy
The Core DVR uses a PPS signal to synchronize to the start of each second. In this way the DVR is always very tightly synchronized with the time provided by an external time receiver. The DVR Express Core 2 and Core 2 MAX have an onboard clock (25ppm) that can drift up to 25us/s by itself. With an external time reference (1Hz), the time is re-synchronized 8 times per second. This results in a ~+- 4us/s timestamp accuracy to the external time source. With an external time reference (20Hz) on Core 2 MAX (GPS ordering option G03-G10) the time is re-synchronized 20 times per second. This results in a ~+-1us/s timestamp accuracy to the external time source.

DVR Timestamp Generation
The default reference for the timestamp of a frame is when FVAL has a rising edge, i.e. the start of frame transfer from the camera to the DVR.  All DVR Express Core DVRs allow triggered time-stamping. This means that a signal can be provided to the DVR to use for the timestamp signal instead of using FVAL.  This is commonly used when cameras are operating in an external trigger mode.  A trigger is sent to the camera to start exposure and the same trigger is sent to the DVR for timestamp triggering.  Thus, the timestamp is applied relative to the start of frame exposure, rather than the start of frame readout.  The DVRs have signal delay elements that can be used to delay this timestamp signal a pre-programmed amount of time. For example. this can be useful to "place" the timestamp in the middle of the exposure period which may better represent the point in time the frame occurred.



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