West Control Solutions Pro-8 - Manual (Page 39)

prevent unreasonably short on and off pulses. The shortest pulses result from ¼
x
t1 or ¼ x t2. The characteristic curve is also called “bath tub curve”.
Parameters to be adjusted: t1 : min. cycle time 1 (heating) [s]
( PArA/ Cntr) t2 : min. cycle time 2 (cooling) [s]
4.4.2 Switching attitude linear (
CyCl= 1 )
For heating ( Y1), the standard method (see chapter 4.4.1) is used. For cooling
( Y2), a special algorithm for cooling with water is used. Generally, cooling is en-
abled only at an adjustable process temperature ( E.H2O), because low temperatu-
res prevent evaporation with related cooling, whereby damage to the plant is
avoided. The cooling pulse length is adjustable using parameter
t.on and is fi-
xed for all output values.
The “off” time is varied dependent of output value. Parameter
t.off is used for
determining the min “off” time. For output of a shorter off pulse, this pulse is
suppressed, i.e. the max. effective cooling output value is calculated according to
formula
t.on / ( t.on + t.off) w 100%.
Parameters to be adjusted: E.H2O: minimum temperature for water cooling
( PArA / Cntr) t.on: pulse duration water cooling
t.off: minimum pause water cooling
4.4.3 Switching attitude non-linear (
CyCl= 2 )
With this method, the cooling power is
normally much higher than the heating
power, i.e. the effect on the behaviour
during transition from heating to coo-
ling may be negative. The cooling cur-
ve ensures that the control intervention
with 0 to -70% correcting variable is
Configuration level
Pro-8
39
Cooling functions
-95% -67% -80%
-100%
-92% -90% -87% -82%
t.off t.on
0,0
1,0
2,0
3,0
4,0
5,0
6,0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
Controller output [%]
relative
cycle
duration
T / T
1
t1
2 x t1
3 x t1
4 x t1