Endress+Hauser Liquiline CM44P - Page 90

Operation Liquiline CM44P
90 Endress+Hauser
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
 82 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
 83 Typical application: dosing pump
Function = Controller
Function Options Info
Actuator type Selection
• None
• Unipolar(-)
• Unipolar(+)
Factory setting
None
Here you specify what part of the controller
should power the relay. Unipolar(+) is the part
of the manipulated variable which the controller
uses to increase the process value (e.g. for
heating purposes). Alternatively, select
Unipolar(-) if you are connecting an actuator to
the relay that reduces the controlled variable
(e.g. for cooling purposes).
Cycle duration
Operating mode = PWM
Shortest turn-on time to
999.0 s
Factory setting
10.0 s
‣
Specify the cycle duration within which the
duty cycle should be varied (only PWM).

The settings for Cycle duration and Shortest turn-on time influence one another. The following applies:
Cycle duration ≥ Shortest turn-on time.
Shortest turn-on time
Operating mode = PWM
0.3 s to Cycle duration
Factory setting
0.3 s
Pulses that are shorter than this limit value are
not output in order to conserve the actuator.