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Re-Arm Time

The re-arm time is the dead time between the end of one segment acquisition and the potential start of the next segment acquisition. During this dead time the data acquisition card is not able to detect a trigger and a potential event will get lost. A short dead time is a key feature for this mode. While competitor products have dead times that can be up to several us or even ms the Spectrum cards have a short dead time that is a fixed number of samples and therfore directly related to the sampling rate.

Re-Arm Time Example

ScreenshotThere is a very small re-arm time between the end of one segment and the trigger being re-armed for the next acquisition. Consider the sine wave with an 88 ns period shown in Figure 6. It was acquired in Multiple Recording mode. The time stamps for all ten segments show a difference of 88 ns, the sine period. This means that no cycles of the 88 ns sine were missed. Remember that the re-arm time is a function of the sample period and the pre-trigger delay. The update rate is the reciprocal of the 88 ns or 11.36 MHz.

Re-Arm Times for different platforms:

The re-arm time depends on the used hardware platform (Hardware Platforms) and is given in samples. The re-arm time is always a fixed number of samples of the currently used sampling clock. For example when acquiring data with 10 MS/s (10,000,000 samples per second) a re-arm time of 4 samples corresponds to 400 ns while a re-arm time of 80 samples when acquiring data with 5 GS/s (5,000,000,000 samples per second) corresponds to 16 ns.

  • M4i, M4x series: Re-Arm time: 40 samples (12, 14, 16 bit) or 80 samples (8 bit)
  • M3i series: Re-Arm time: 32 samples (12, 14, 16 bit) or 64 samples (8 bit)
  • M2i series: Re-Arm time: 4 samples
  • MX series: Re-Arm time is series and settings depending: < 20 samples
  • MC series: Re-Arm time is series and settings depending: < 20 samples
  • MI series: Re-Arm time is series and settings depending: < 20 samples

Resulting Dead-Time

The re-arm time reflects the time between end of a segment acquisition until the next acquisition can start and the card can switch to trigger armed status again. However after the re-arm time has elapsed there's still the pre-trigger area to be filled until the digitizer can detect the next trigger event. The minimum pre-trigger area depends on the card family and is specified inside the data sheet of your particilar product.

The following drawing shows the relation between the different timings and signals. Please click to enlarge.

Re-Arm Time and repetition rate

A short re-arm time is a key figure to acquire fast signal repetition rates:   More

 

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