JUMO 709061 TYA 201 - Single-Phase Power Controller Operating Manual - Manual (Page 78)

6 Special device functions
76 2012-12-01/00561071 [SCR Power Controller TYA201]
6.5 Subordinate control
Subordinate control loops are used to eliminate or compensate for external in-
terference, such as fluctuations in the supply voltage and changes in resis-
tance which would have a negative effect on the control loop.
6.5.1 Closed control loop without subordinate control
Example
Furnace/kiln
control system The supply voltage is connected to the power controller. The controller derives
the output level y
R
from the difference between the set value (w) for the fur-
nace temperature and the actual value (x) which is acquired by a sensor inside
the furnace. The output level can vary over the range 0 to 100 % and is output
as a standard signal, for example 0 to 10 V. The output level is fed to the pow-
er controller.
The task of the power controller is to feed energy to the heating elements in
the furnace, proportional to the controller output level:
- For an SCR power controller using phase angle control, this means that
it alters the firing angle over the range from 180 ° to 0 °, corresponding to a
controller output level of 0 to 100 %.
- If the SCR power controller is using the burst-firing mode, it increases
the duty cycle T from 0 to 100 %, corresponding to a controller output level
of 0 to 100 %.
If the supply voltage drops from AC 230 V to AC 207 V (-10 %) at a controller
output level YR, the power fed to the furnace is reduced by 19 %.
P
230V
: Power in the load resistance at a supply voltage U of 230 V
Δ
P: Power reduction resulting from reduced supply voltage
R: Resistance of the load
This 19 % reduction in the energy being fed in means that the
furnace temperature falls.
Disadvantage: A continuing constant temperature is no longer assured.
The power controller recognizes the deviation through the relatively slow re-
Controller
Furnace
Sensor
SCR
power unit
Supply
voltage
y
R
x
y
-
w
(2) P
230V
Δ P –
U 0 – 1U , ( )
2
R
--------------------------
0 9U , ( )
2
R
------------------
0,81 P
230 V
• = = =