Data Sheet for Product
Siemens Building Technologies CA1N4028 / 11.1998
Landis & Staefa Division 7/12
The control benefits
The quality of a control loop depends on a number of separate factors: the
characteristics of the controlled system and its various elements (expressed
quantitively as the ‘degree of difficulty’), the controller settings and, to a
large extent, the control properties of the hydraulic valve. In this context,
the relevant questions are:
• How quickly does the valve respond to a control deviation?
• How high is its resolution?
• How effectively does it control partial loads?
The development engineers at Landis & Staefa based their work on these
questions when designing the modulating magnetic valve, the product
which first established the company's success. Throughout the process of
continuing improvement and expansion of this market offering, the initial
set of questions has remained unchanged, even in the age of widespread
DDC technology in the field of HVAC controls.
Fast positioning
The simple design principle on which the magnetic actuator is based – a
single moving part, the core, within a changing magnetic field – results in
very fast positioning. Within the control loop, the magnetic valve is a
virtually delay-free element. This has the following consequences:
• Fast elimination of interference variables
• The valve responds immediately to setpoint adjustments.
• The degree of difficulty S
v
= T
u
: T
g
of the control loop is reduced
significantly : from 0.48 to 0.36 (i.e. 25 %) for example, as shown by
comparative measurements in systems with magnetic and conventional
valves (see Fig. 13).
94.0142
x
S = 0.36
S = 0.48
t
[s]
T
g
T
g
T
u
T
u
Fig. 13: Effect of positioning speed on degree of difficulty
Fig. 14: Admissible loop
gain V
o
A reduced degree of
difficulty, however, also
means that the admissible
loop gain can be increased.
The number of lag inducing
elements in the controlled
system can be reduced by
one (see Fig. 14).
94.0143
V
0
0.03 0.05 0.07 0.1 0.2 0.3 0.5 0.7 1
1
2
3
4
5
7
10
20
30
40
50
70
100
3
4
5
6
7
8
9
10
= S
T
u
T
g