Arming, in general, gives the opportunity to start and stop a measurement when an external qualifier event occurs.
Arming can initialize either a single sample acquisition (Arm on Sample) or a single measurement session defined by sample count (Arm on Block). Measurement can be started and stopped by rising or falling edge of signals on instrument’s inputs and delayed from 0 ns (delay off) to 2 s with 10 ns resolution step. In case of Totalize measurement mode, timer (set by a combination of Sample Interval and Stop Source set to Timer) can be used as a source of stop arming.
Table 1 shows possible arming modes and their specifics. Modes absent in this table are not supported.
| Start Arming Source | Stop Arming Source | Arm on | Measurement Function | Comment |
| Off | Off | N/A | Any | Arming is not used, measurement is started and stopped normally |
| Input | Off | Block | Any, except Totalize | Start arming input initialize measurement session (block). Measurement session ends when all samples (number is set by Sample Count) have been collected.  Figure 12. Frequency measurement with measurement session repeated after start arming pulses Arming start pulses that occur during measurement session are neglected (see ).  Figure 13. Frequency measurement with arming start pulses occurring during the measurement session |
| Input | Input | Block | Any, except Totalize | Start arming starts measurement session (block). Measurement session ends when either all samples (number is set by Sample Count) have been collected or by signal front on stop arming input (whatever comes first).  Figure 14. Frequency measurement with measurement session controlled by start and stop arming signals |
| Off | Timer | Sample | Totalize | Totalize measurement is started by pressing Restart button, Sample Interval defines Totalize Gate length. The Analyzer counts number of events during the gate and produces single sample (1 sample per series). |
| Input | Timer | Sample | Totalize | Start arming pulses start Totalize Gates (gate length is defined by Sample Interval). Each gate produces 1 sample (per series). Measurement session ends once required number of samples (set by Sample Count) was collected.  Figure 15. Totalize measurement in timed mode (stop arming signal set to timer) |
| Input | Off | Sample | Any, except Totalize | Start arming is used as a pacing clock – single sample measurement is executed just after the arming event.  Figure 16. Pulse width measurement with arming signal used as a pacing clock In case of Frequency/Period Average measurement, samples are measured with dead-time, no back-to-back. Maximum total number of samples is reduced to up to 16 million.  Figure 17. Frequency measurement initialized by arming pulses |
| Input | Input | Sample | Totalize, Frequency, Period Average, Smart Frequency, Smart Period Average | Start arming events start Gate (gate length is defined by Sample Interval). Stop arming events end Gate. Each gate produces 1 sample (per series). Measurement session ends once required number of samples (set by Sample Count) was collected. In case start and stop arming settings are not the same, neasurements are performed with dead-time, no back-to-back. Maximum total number of samples is reduced to up to 16 million.  Figure 18. Frequency measurement in a gate created by arming signals When arming start and stop conditions are the same, measurements are performed continuously (back-to-back) with no dead-time.  Figure 19. Frequency measurement when arming stop is set the same as arming start (back-to-back measurements) In case Smart versions of Frequency/Period Average are used, each sub-gate (Sample Interval divided by 1000) is being armed, i.e. one sample is calculated using data from 1000 arming gates. |
| Input | Input | Sample | Any, except Totalize, Frequency, Period Average, Smart Frequency, Smart Period Average | Start arming is used as a pacing clock – a single sample measurement is executed just after active edge of arming pulse. Stop arming delays registration of timestamps other than the first one. Depending on particular measurement mode, two, three or four timestamps are registered that give a single result.  Figure 20. Pulse width measurement with arming on sample and start and stop arming active, case 1  Figure 21. Pulse width measurement with arming on sample, start and stop arming active, case 2 |
Start arming is useful for measurement of frequency in signals, such as the following:
- Pulse modulated RF signals (bursts) Single-shot events or non-cyclic signals.
- Pulsed signals where pulse width or pulse positions can vary. Signals with frequency variations versus time (“profiling”).
- A selected part of a complex waveform signal.
Signal sources that generate complex wave forms like pulsed RF, or sweep signals, usually also produce a sync signal that coincides with the start of a sweep, or start of a radar burst. These sync signals can be used to arm the Analyzer. See Figure 21.
You normally use stop arming together with start arming. That means that the external gating signal controls both the start and the stop of the measurement. Such a gating signal can be used to measure the frequency of an RF burst signal. Here the position of the external gate must be inside a burst. See Figure 22.
Note that burst measurements with access to an external sync signal are performed in the normal Frequency mode. In time interval measurements, you can use the stop arming signal as a sort of “external trigger Hold Off signal”, blocking stop trigger during the external period. See Figure 24.
Please note: start arming setup time is up to 5 ns. Which means that the measurement is actually started within 5 ns since start arming event.