Balluff MATRIX VISION mvBlueNAOS, Technical Manual

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1.18 Use Cases 195
Note
Be aware of the drift of the individual timestamps.
The timestamp is generated via FPGA in the camera which itself is clocked by a crystal oscillator.
This is done independently in each camera and by default not synchronized among cameras or the host
system.
Typical stability of crystal oscillators is in the range 100ppm (parts per million).
I.e. for longer operation times (say in excess of hours) there is a tendency that timestamps of indi-
vidual cameras drift against each other and against the time in the operating system of the host.
Customers wishing to use the individual camera timestamps for synchronization and identification
of images via timestamps for multi-camera systems will have in the meantime
- to reset all timestamps either by hardware signal or by command and regularly resynchronize or check
the drift algorithmically
- in order to make sure that the drift is less half an image frame time.
1.18.6.3 Synchronizing camera timestamps
1.18.6.3.1 Introduction
Camera timestamps are a recommended Genicam (p. 113 ) / SFNC (p. 121 ) feature to add the information when an
image was taken (exactly: when the exposure of the image started).
Without additional synchronization it is merely a camera individual timer with a vendor specific increment and im-
plementation dependent accuracy. Each camera starts its own timestamp beginning with zero and there are no
means to adjust or synchronize them among cameras or host PCs. MATRIX VISION cameras offer several ways of
synchronizing:
• mvTimestampReset (p. 195 )
• Pulse-per-second signal (PPS) (p. 197 )
• mvDeviceTimeSync (p. 199 )
The usage is described below.
1.18.6.3.2 Without Precision Time Protocol (PTP) IEEE1588
There are many applications which do not or cannot profit from "IEEE1588" but have certain synchronization needs.
Solutions for these scenarios are describes as follows.
1.18.6.3.3 Synchronizing using mvTimestampReset
First of all the standard does not provide hardware means to reset the timestamp in a camera other than plug off and
on again. Therefore MATRIX VISION has created its own mechanism
mvTimestampReset to reset the timestamp
by a hardware input.
MATRIX VISION GmbH