BNC 1105 Universal Counter - Manual (Page 53)

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Sensitivity at a particular frequency is the lowest amplitude signal to
trigger the counter for counting. The amplifier gain and the voltage
difference between the trigger hysteresis levels determine the sensitivity
of the counter. Sensitivity is specified by the upper and lower levels with
the trigger level fixed at the middle. The input signal must cross both the
upper and lower levels in order to trigger a count as shown in Figure 4-12.
If the peak-to-peak amplitude of a signal does not exceed the limits, this
signal will not trigger a count as shown in Figure 4-13. Moreover, the
counter also won’t do a count as the trigger level which is set below the
midpoint of the signal can’t cross the limit as shown in Figure 4-14.
Figure 4-12 Figure 4-13
Figure 4-14
Triggering menu is associated with input channel. Press CH1 or CH2 and
the softkey under TRIG SENS as shown in the Figure 4-15 to enter the
menu. Then follow the instructions below for different operations:
Figure 4-15
To turn on/off auto triggering: press the softkey under AUTO to
toggle between ON and OFF as shown in the Figure 4-16.