Hanna Instruments HI520 - Page 91

91 Control Modes & Algorithms
Analog Output is proportional with Set point variance over Control period.
SP
Control period
Control mode
High
Control mode
Low
Deviation
Process value
Analog out
Analog out
20 mA
0/4 mA
20 mA
0/4 mA
Figure 33: Proportional Control, Analog Out ‑ Control Mode High and Low
Running control On continuously for an extended period of time is prevented by Overtime control action.
SP
Control period
Proportional control
mode High
Overtime
Deviation
Process value
Rela
y out
Alarm condition
Figure 34: Proportional Control, Relay Out ‑ Proportional Control Mode High, Overtime
Relay On time has a guaranteed minimum to prevent stressing the actuators electrically or mechanically.
SP
Relay out
Control period
Proportional control
mode High
Deviation
Process value
Relay out with min.
On time control action
Min. On time
On
Off
Figure 35: Proportional Control, Relay Out, Proportional Control Mode High, Min. On Time