The Multiple Recording mode allows the recording of several trigger events with an extremely short re-arming time. The hardware doesn't need to be restarted in between. The on-board memory is divided in several segments of the same size. Each of them is filled with data if a trigger event occurs. Pre- and posttrigger of the segments can be programmed. The number of acquired segments is only limited by the used memory and is unlimited when using FIFO mode.
Significant data associated with multiple triggers is stored in the acquisition memory in the contiguous segments. Data associated with the dead-time between events is not recorded. Each trigger event is time stamped so the precise location of each trigger is known. The timestamps are stored in an extra FIFO memory that is located in hardware on the card. It can be read out if needed much as the data is.
Advantages of Multiple Recording Mode
- The re-arm or trigger "dead-time" is reduced extremely in multiple and gated modes compared with single-shot acquisitions. A low trigger re-arm time means you reduce the chance of missing an event even in high event rate applications.
- Segmentation of the acquisition memory allows more efficient use of memory by recording data at full sample rate only when the signal is active.
- The storage of only significant measurement events without the intervening "dead-time" results in less data to be transferred and allows continuous data acquisition and processing of segmented signals.
- The Timestamp of each trigger event allows you to read the time difference between events. When the events represent abnormalities in the signal, timestamps provide information on the rate of occurrence of the anomalies.
- Timestamps can by synchronized to an external reference signals such as a radio clock or IRIG-B timing generator to get UTC synchronized timestamp information on every event.
The example shows a Multiple Recording mode acquisition of the acoustic output of an ultrasonic range finder. This device outputs 40 kHz bursts and determines range by detecting the time it takes until an echo is received. The bursts occur in groups of five at a spacing of 15 s with processing taking place in the 450 ms "dead-time" between these multiple bursts. The acoustic signal was picked up using an instrumentation microphone with a bandwidth of 100 kHz. The settings on the left side of the figure show the setup of the acquisition. Each segment consists of 32kS with 1kS of pre-trigger and 31kS of post-trigger recording. The sample rate, not shown, is 7.8 MS/s. The upper trace is a preview of the entire acquisition showing the multiple bursts and the processing intervals. The center trace is a zoom view showing five segments. The beginning of each segment is marked with a time stamp. The bottom trace is a zoom view of the first burst in the acquisition. Here you can see the details of the individual burst. The software displaying this data can show the segments contiguously as they are actually stored in memory but the view incorporating the measured spacing is generally more useful. By storing only the segments associated with each trigger the digitizer eliminates over 3.5 MSamples (MS) of data that would have been consumed in recording each instance of the dead time.
Re-Arm time (dead 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. More info on re-arm time
Limitations of MICX platform in Multiple Recording Mode
This chapter is valid for all products based on MICX platform driver. Read More
Products based on the MICX platform do not have a programmable pretrigger area in Multiple Recording mode. Instead the pretrigger is a small fixed number of samples. The size of the pretrigger inhere depends on the speed and number of activated channel and can be found in the hardware manual.