LC/TOF-MS and GC/TOF-MS applications generate much higher ion rates than quadrupole/quadrupole/TOF-MS, because the output of the chromatograph feeds the time-of-flight mass spectrometer directly. In this case, the number of ions detected in any of the prominent peaks is normally much greater than one for each acceleration pulse. A TDC cannot work in this application, because it is limited to single-ion pulses. The optimum solution is therefore a Model 9326-P Preamplifier and a FASTFLIGHT-2 Digital Signal Averager, as illustrated in the figure below.

The FASTFLIGHT-2  signal averager triggers the acceleration pulse generator, which accelerates the ions as they arrive from the chromatograph into the flight tube. Alternatively, the acceleration pulse generator can be used to trigger the FASTFLIGHT-2 averager, which may be simpler to configure if the averager is replacing a fast oscilloscope or similar instrument, although this can give slightly increased jitter. Each ion that arrives at the microchannel plate detector causes a small pulse signal which is then amplified by the Model 9326-P preamplifier to match the input range of the digital signal averager. At its input, the FASTFLIGHT-2 incorporates an ADC (analog-to-digital converter) that periodically samples the input voltage at 500 ps intervals, and converts those samples to an 8 bit digital representation. The amplitude of the sampled signal is proportional to the number of molecular ions simultaneously arriving at the detector, while their arrival time is determined by the sampling time at the maximum amplitude of the pulse. For better statistical precision, the centroid of the sampled pulse can be used to define the arrival time, which ultimately identifies the mass-to-charge ratio of the molecular ion.

To improve the signal-to-noise ratio, time-of-flight records from a large number of acceleration pulses are summed (and thereby linearly averaged) in the FASTFLIGHT-2 hardware memory. The final, summed spectrum is compressed and passed to the supporting computer to display the chromatograph, and to save the data to hard disk. Each point in the chromatograph incorporates a time-of-flight spectrum, which also can be displayed. This scheme thrives on high ion rates, and can support sustained acquisition rates up to 100 averaged spectra/second in the chromatograph/TOF-MS mode.