West Control Solutions KS98-1 - Manual (Page 234)

D / Y / off
The principle is identical to the control behaviour of a 2-point controller with additional contact.
Output Y2 is used for switchover of the connected circuit between “
D” and “Y”. Output Y1 switches the heating ener-
gy on and off.
E.g. for temperature control with electrical heating (inverse operation) or cooling (direct operation).
Cycle time Tp1 must be adjusted as follows: Tp Tu 1 0 25 <= · , With higher Tp1, oscillations must be expected. Tp1 cor-
responds to the minimum cycle time (time in seconds) at 50 % duty cycle.
PD action
( Tn = 0 = switched off Tn = Î)
The working point is in the middle of the proportional band X
p1
at 50 % duty cycle.
For keeping the control variable constant, a defined amount of energy dependent of is required. This causes a perma -
nent control deviation, which increases with higher X
p1.
DPID action
By means of the I action, line-out without permanent control deviation is possible.
The static characteristic of a two-point controller is identical to the one of a continuous controller. The difference is
that a duty cycle instead of a linearly variable current signal is output (relay contact, logic signal 0/20mA or control
output 0/24V).
Working point Y
0
and cycle time Tp1 of the cycle at 50% are adjustable.
The shortest switch-on or off time is 100ms.
Controller 9499-040-82711
III-234 Control behaviour
Output Y1 (heating)
Output Y2 (add. contact)
Process value
Setpoint
Xn100 Xn0 W0 Weff W100
100%
0%
Y1Â
Y2Â
Xeff
Xp1
LW Xsd2
actual
working point
Fig.: 57
Fig. Static operating principle
of the
D / Y / off function