Agilent Technologies TV 551 Notice De Mode D'emploi page 227

PROGRAMMABLE SET POINT: this open collector output signal is
enabled when the reference quantity chosen (frequency, current or
time) is higher than the set threshold. The signal can be "high level
active" (that is the output is normally at 0 Vdc and becomes 24 Vdc
when activated), or "low level active" (that is the output is normally
at 24 Vdc and becomes 0 Vdc when activated). Moreover, if the
reference quantity is the frequency or the current drawn, it is
possible to set the hysteresis (in % of the threshold value) to avoid
bouncing.
For example:
Figure 18
The set point output stays at 0 Vdc until the frequency becomes
higher than 505 Hz (that is 500 Hz + 1 % of 500 Hz), then the output
goes at 24 Vdc and stays at 24 Vdc until the frequency becomes lower
than 495 Hz (that is 500 Hz – 1 % of 500 Hz).
TV 551/701 SEM Navigator User Manual / 87-900-958-01(G)
reference quantity: frequency
threshold: 500 Hz
hysteresis: 1 %
activation type: "high level"
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