Endress+Hauser Liquiline CA80SI - Page 84

Operation Liquiline System CA80SI
84 Endress+Hauser
Outputting the manipulated variable of a controller
To output a controller manipulated variable via a relay, the relay is modulated. The relay is
energized (pulse, t
1
) and is then de-energized (interval, t
0
).
Function = Controller
Function Options Info
Source of data Selection
• None
• Controller 1
• Controller 2
Factory setting
None
‣
Select the controller that should act as the
data source.
Operating mode Selection
• PWM
• PFM
Factory setting
PWM
PWM=pulse width modulation
PFM=pulse frequency modulation
1. PWM (pulse width modulation):
The duty cycle is varied within a period T (T=t
1
+t
0
). The cycle duration remains
constant.
0
T
t
1
t
0
2T 3T
y = t / T
1
10 % 50 % 100 %
1 "High"
0 "Low"
t
 65 Typical application: solenoid valve
2. PFM (pulse frequency modulation):
Here, pulses of a constant length (t
1
) are output and the interval between the pulses
varies (t
0
). At a maximum frequency, t
1
= t
0
.
1 "High"
0 "Low"
T
t
t
1
t
0
2T
y = f / f = T / T
max min
100 % 50 %
20 %
3T
 66 Typical application: dosing pump