Three-point controller 232, Three-point controller – West Control Solutions KS98-1 User Manual

Page 232

Three-point controller

Switching controller with three switching statuses:

1. Heating switched on;

r output Y1 = 1, Y2 = 0

2. Heating and cooling switched off;

r outputs Y1 = 0, Y2 = 0

3. Cooling switched on;

r outputs Y1 = 0, Y2 = 1

E.g. for temperature control with electrical heating (h) and cooling (c).

Adjust cycle time

Tp1 and Tp2 as follows:

0 25

(h) Tp

0 25

(c).

With higher

Tp1/Tp2, oscillations have to be expected. Cycle times Tp1 and Tp2 are the minimum cycle times

at 50% duty cycle.

PD/PD action
(

Tn = 0 = switched off Tn = Î)

The positioning range reaches from 100 % heating (Y1) to 100 % cooling (Y2). The proportional bands must be adapted to the
various heating and cooling power values. In order to keep the control variable constant, a defined amount of energy depen-
dent of is required. This causes a permanent control deviation, which increases with growing X

p(1,2).

DPID/DPID action
By means of the I action, line-out without permanent control deviation is possible. Transition from trigger point 1 (hea-
ting) to trigger point 2 (cooling) is without neutral zone. The proportional bands must be adapted to the various heating
and cooling power values.

Fig.: shows the static characteristic for inverse output action.

Direct/inverse switchover only causes exchanging of the outputs for “heating/cooling”.
Expressions “heating” and “cooling” may also mean similar processes (dosing acid/lye, ...).

The neutral zone is adjustable separately for the trigger points (X

sh1

, X

sh2

) i.e. it need not be symmetrical to the .

The type of positioning signals is selectable:

CFunc = 3-point

heating switching,

cooling switching

CFunc = cont/switch

heating continuous,

cooling switching

CFunc = switch/cont

heating switching,

cooling continuous

Combination “heating continuous” and “cooling continuous” is covered by “splitRange - continuous controller with
split-range behaviour”. r see also "continuous controller" page: 238.

Controller

9499-040-82711

III-232

Control behaviour

Output Y1 (heating)
Output Y2 (cooling)

Process value

Setpoint

100%

Y1Â h

Y2Â c

Xn100

Xn0

Weff

W100

Xeff

Xp2

Xp1=Xp'+Xp''

Xp'

Xp''

Xsh1 Xsh2

actual

working point

Fig.: 56
Static operating principle

of a three-point controller