Endress+Hauser Liquisys M CUM253 - Page 50

Commissioning Liquisys M CUM223/253
50 Endress+Hauser
Control and fine optimization of the set parameters with a recorder
Actuating signal outputs (R237 to R2310)
Each control contact outputs a cyclical signal whose intensity corresponds to the controller's
manipulated variable. A distinction is made according to the type of signal cycle:
• Pulse length modulation
The bigger the calculated manipulated variable is, the longer the contact affected remains
picked up. The period T can be adjusted between 0.5 and 99 s (field R238). Outputs with
pulse length modulation are used to activate solenoid valves.
• Pulse frequency modulation
The bigger the calculated manipulated variable is, the higher the switching frequency of
the contact affected. The maximum switching frequency 1/T can be set between 60 and
180 min
-1
. The on-time t
ON
is constant. It depends on the set maximum frequency and is
approx. 0.5 s for 60 min
-1
and approx. 170 ms for 180 min
-1
. Outputs with pulse frequency
modulation are used to activate directly controlled solenoid dosing pumps.
a0008924
Optimization of settings T
n
and K
p
A
B
Actual value
Time
1
2
3
T
n
too small
T
n
too large
K
p
too large
4
5
K
p
too small
Optimum setting
a0008928
Fig. 27: Signal of a pulse-length modulated controller contact (left) and of a pulse-frequency modulated controller contact (right)
A
B
Contact 1 = on, 0 = off
Time [s] t
1
= t
on
t
2
= t
off
T
T
1
T
2
Period length
Impulse period length (impulse freq. 1/T
1
and 1/
T
2
)
A
B
A
B
A
B
A
B
A
B
1
2
3
4
5
A
1
0
T
t [s]
A
t [s]
t
1
t
2
t
1
1
0
T
1
T
2