Hach-Lange SI794 P User Manual - Manual (Page 86)

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Controller functions
Pulse length / pulse frequency controller
Pulse length controller (PLC)
The pulse length controller is used to operate a valve as an actuator.
It switches the contact on for a time that depends on the controller
output. The period is constant. A minimum ON time of 0.5 sec is
maintained even if the controller output takes corresponding values.
Pulse frequency controller (PFC)
The pulse frequency controller is used to operate a frequency-
controlled actuator. It varies the frequency with which the
contacts are switched on. The maximum pulse frequency
[pulses/min] can be defined. It depends on the actuator.
The contact ON time is constant. It is automatically calculated
from the user-defined maximum pulse frequency:
Output signal (relay contact) of pulse length controller
Output signal (relay contact) of pulse frequency controller
ON time (Y = 80 %)
ON time (Y = 20 %)
Pulse length
0
0
ON time
Pulse frequency (Y = 20%)
1
0
1
0
Pulse frequency (Y = 80%)