HP 53131A Operating Manual page 122

Chapter 2 Operating Your Universal Counter
Using CHANNEL 1 and CHANNEL 2 Input Conditioning Keys
DEFINITION OF SENSITIVITY. Sensitivity is the lowest amplitude
signal at a particular frequency that the Counter will count. The amplifier
gain and the voltage difference between the input trigger hysteresis levels
determine the Counter's sensitivity. Sensitivity is specified with the
trigger level set at a value equal to the midpoint of the input signal.
The input waveform must cross both the upper and lower hysteresis levels
to generate a count as shown in the following figure.
Upper
Hysteresis
Level
Peak-to-Peak
Sensitivity
Lower
Hysteresis
Level
Signal crosses through both hysteresis levels to effect a count.
If the signal peaks do not exceed beyond both hysteresis limits, the input
signal will not generate a count. For example, the peak-to-peak amplitude
is insufficient, or trigger level is set above or below the midpoint of the
input signal as shown in the following figures.
Upper
Hysteresis
Level
Peak-to-Peak
Sensitivity
Lower
Hysteresis
Level
Signal will not generate a count because the peak-to-peak amplitude of
the signal is insufficient.
2-46
Trigger
Level
Input signal
to Counter
Trigger
Level
Input signal
to Counter
Operating Guide