Search

You are here

Using an IRIG-B, GPS or radio clock source as reference signal for timestamps | Spectrum

Timestamp Theory

timestamp reference clock mode timingThe timestamp mode is used to get precise timing information of the received trigger signal. For this an internal timestamp counter is running permanently, driven by the sampling clock. If a trigger is recognized and an acquisition takes place, this timestamp counter is stored into a separate memory and can be read out afterwards.

The timestamp of the Spectrum digitizers can run in different counting modes. One mode, called timestamp reference clock mode, uses an external signal to synchronize to. The timestamp counter is split into two parts then, the lower part using the sampling clock as before and the upper part of the counter using the external reference signal as counting pulse (please see picture to the right, click to enlarge).

Combining the information of acquisition starting time (stored by the driver), reference clock signal count and timestamp sampling clock count, one gets a very precise absolute time information when the trigger signal has been received. This information can be used to synchronize acquisitions that have been done on different locations (like power line failures spread across the country) or the acquisition can be taken into relation to external events.

Connection of the reference signal

System setup of digitizer and IRIG-B receiverThe timestamp reference clock signal is normally a simple TTL signal that has a timing of one 1 Hz (1 pulse per second). This timing signal can be taken from a GPS receiver, a radio clock or an IRIG-B receiver. The right hand picture (click to enlarge) shows the setup for a M2i.2030 200 MS/s digitizer in combination with an IRIG-B receiver card.

The timestamp reference signal is connected to the Spectrum digitizer in different ways depending on the card family you're using:

  • digitizerNETBOX series: connection through connector on front plate
  • generatorNETBOX series: connection through connector on front plate
  • M4i series: connection through the extra I/O lines connector on front plate
  • M4x series: connection through the extra I/O lines connector on front plate
  • M3i series: connection through the extra I/O lines connector on front plate
  • M2i series: separate option BASEXIO or BASEXIO2 is needed as shown in picture
  • MC series: timestamp module with extra connection needed. Please contact factory
  • MX series: no timestamp available
  • MI series: timestamp module with extra connection needed. Please contact factory

PC time synchronization

Please note that it is necessary to use the same source as time synchronization to the PC as the driver stores the starting time using the time information of the PC. For the digitizerNETBOX the time information of the host PC is used as the driver is running there. There are different ways how to ensure that the time information for the driver is valid:

  • Place the timing receiver inside the PC as shown in the picture above (inside the host PC for digitizerNETBOX series)
  • Use a precise time synchronization in your network that is based on the same time network (like global IRIG-B synchronization)